Module 2 MCA-105 Structured Programming in C ADMN 2011-‘14

MODULE 2
OPERATORS AND EXPRESSIONS
2.1 OPERATORS INTRODUCTION
An operator is a symbol which helps the user to command the computer to do a
certain mathematical or logical manipulations. They are used in programs to manipulate data
and variables. C has a rich set of operators which can be classified as:
1. Arithmetic operators
2. Relational Operators
3. Logical Operators
4. Assignment Operators
5. Increments and Decrement Operators
6. Conditional Operators
7. Bitwise Operators
8. Special Operators
All the basic arithmetic operations can be carried out in C. All the operators have
almost the same meaning as in other languages. Both unary and binary operations are
available in C language. Unary operations operate on a single operand; therefore the number
5 when operated by unary will have the value 5.

1. Arithmetic Operators

Operator Meaning
+ Addition or Unary Plus
– Subtraction or Unary Minus
* Multiplication
/ Division
% Modulus Operator

(Table: 2.1)
Examples of arithmetic operators are
x+y
x-y
-x + y
a*b+c
-a * b
etc.,
Here a, b, c, x, y are known as operands. The modulus operator is a special operator in
C language which evaluates the remainder of the operands after division. It acts only on
integer operands.
Integer Arithmetic
When an arithmetic operation is performed on two whole numbers or integers
than such an operation is called as integer arithmetic. It always gives an integer as the result.
Let x = 27and y = 5 be 2 integer numbers. Then the integer operation leads to the following
results.

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x+y = 32
x – y = 22
x * y = 115
x%y=2
x/y=5
In integer division the fractional part is truncated.
Floating point arithmetic
When an arithmetic operation is preformed on two real numbers or fraction numbers
such an operation is called floating point arithmetic. Operands will assume either decimal or
exponential notation. The floating point results can be truncated according to the properties
requirement. The remainder operator (%) is not applicable for floating point arithmetic
operands.
Let x=14.0 and y=4.0 then
x+y=18.0
x-y=10.0
x*y=56.0
x/y=3.50
Mixed mode arithmetic
When one of the operand is real and other is an integer and if the arithmetic operation
is carried out on these 2 operands then it is called as mixed mode arithmetic. If anyone
operand is of real type then the result will always be real thus 15/10.0 = 1.5

2. Relational Operators
Often it is required to compare the relationship between operands and bring
out a decision and proceed accordingly. This is when the relational operator comes into
picture. C supports the following relational operators.

Operator Meaning
is<less than less than
is<=less than less than or equal to
is>greater thgreater than
is>=greater thgreater than or equal to
is!=not equal not equal to
is==equal toe equal to

(Table: 2.2)
It is required to compare the marks of 2 students, salary of 2 persons; we can compare
them using relational operators. A simple relational expression contains only one relational
operator and takes the following form.
exp1 relational operator exp2
Where exp1 and exp2 are expressions, which may be simple constants, variables or
combination of them. Given below is a list of examples of relational expressions and
evaluated values.
6.5<=25 TRUE
-65>0 FALSE

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10 < 7 + 5 TRUE
The value of a relational expression will be „0‟ if the expression is false and it will be „1‟ if
the expression is true.
Relational expressions are used in decision making statements of C language such as
if, while and for statements to decide the course of action of a running program.

3. Logical Operators
Logical operators are used when we want to test more than one condition and make
decision. It combines 2 or more relational expressions. The value of a logical expression will
be „0‟ if the expression is false and it will be „1‟ if the expression is true.
Operator Meaning
&& Logical AND
|| Logical OR
! Logical NOT

(Table: 2.3)
1.Logical AND (&&)
This operator is used to evaluate 2 conditions or expressions with relational operators
simultaneously. If both the expressions to the left and to the right of the logical operator is
true then the whole compound expression is true.
Example:
a > b && x = = 10
The expression to the left is a > b and that on the right is x == 10 the whole expression
is true only if both expressions are true i.e., if a is greater than b and x is equal to 10.
2.Logical OR (||)
The logical OR is used to combine 2 expressions or the condition evaluates to true if any
one of the 2 expressions is true.
Example :
a < m || a < n
The expression evaluates to true if any one of them is true or if both of them are true.
It evaluates to true if a is less than either m or n and when a is less than both m and n.
3.Logical NOT (!)
The logical not operator takes single expression and evaluates to true if the expression is
false and evaluates to false if the expression is true. In other words it just reverses the value
of the expression.
Example :
! (x >= y) the NOT expression evaluates to true only if the value of x is neither greater than
or equal to y

4. Assignment Operator(=)
General for of a statement containing assignment operator is:
variable_name=expression;
The value of expression is evaluated and the content of the location „variable_name‟ is
replaced by expression value. Operand to left of assignment operator should be a variable and
its right operand can be any arbitrary expression.

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Example:
x=a+b
Here the value of a + b is evaluated and substituted to the variable x.
In addition, C has a set of shorthand assignment operators of the form.
var oper = exp;
Here var is a variable, exp is an expression and oper is a C binary arithmetic operator. The
operator oper = is known as shorthand assignment operator
Example:
x + = 1 is same as x = x + 1 .The commonly used shorthand assignment operators are as
follows

Statement with simple Statement with

assignment operator shorthand operator

a=a+1 a += 1
a=a–1 a -= 1
a = a * (n+1) a *= (n+1)
a = a / (n+1) a /= (n+1)
a=a%b a %= b

(Table: 2.4)
Example for using shorthand assignment operator
#define N 100 //creates a variable N with constant value 100
#define A 2 //creates a variable A with constant value 2
main() //start of the program
{
int a; //variable a declaration
a = A; //assigns value 2 to a
while (a < N) //while value of a is less than N
{ //evaluate or do the following
printf(“%d \n”,a); //print the current value of a
a *= a; //shorthand form of a = a * a
} //end of the loop
} //end of the program
Output
2
4
16
If 2 operands in an assignment expression are of different types, the value of expression on
right hand side is automatically converted to the type of identifier on left.
Note: It is possible to have multiple assignments in a single line.
i=j=2;

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5. Increment and Decrement Operators

The increment and decrement operators are one of the unary operators which are very
useful in C language. They are extensively used in for and while loops. The syntax of the
operators is given below
1. ++ variable name
2. variable name++
3. – –variable name
4. variable name– –
The increment operator ++ adds the value 1 to the current value of operand and the
decrement operator – – subtracts the value 1 from the current value of operand. ++variable
name and variable name++ mean the same thing when they form statements independently,
they behave differently when they are used in expression on the right hand side of an
assignment statement.
Consider the following
m = 5;
y = ++m; (prefix)
In this case the value of y and m would be 6
Suppose if we rewrite the above statement as
m = 5;
y = m++; (post fix)
Then the value of y will be 5 and that of m will be 6. A prefix operator first adds 1 to the
operand and then the result is assigned to the variable on the left. On the other hand, a postfix
operator first assigns the value to the variable on the left and then increments the operand.

6. Conditional or Ternary Operator

The conditional operator consists of 2 symbols the question mark (?) and the colon (:)
The syntax for a ternary operator is as follows
exp1 ? exp2 : exp3
The ternary operator works as follows
exp1 is evaluated first. If the expression is true then exp2 is evaluated & its value becomes
the value of the expression. If exp1 is false, exp3 is evaluated and its value becomes the value
of the expression. Note that only one of the expressions is evaluated.
For example:
a = 10;
b = 15;
x = (a > b) ? a : b
Here x will be assigned to the value of b. The condition follows that the expression is false
therefore b is assigned to x.

/* Example : to find the maximum value using conditional operator)

#include <stdio.h>
void main() //start of the program
{
int i,j,larger; //declaration of variables

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printf (“Input 2 integers : ”); //ask the user to input 2 numbers

scanf(“%d %d”,&i, &j); //take the number from standard input and store it
larger = i > j ? i : j; //evaluation using ternary operator
printf(“The largest of two numbers is %d \n”, larger); /* print the largest number*/
} // end of the program
Output
Input 2 integers : 34 45
The largest of two numbers is 45

7. Bitwise Operators
C has a distinction of supporting special operators known as bitwise operators for
manipulation data at bit level. A bitwise operator operates on each bit of data. Those
operators are used for testing, complementing or shifting bits to the right on left. Bitwise
operators may not be applied to a float or double.

Bitwise AND(&)
The bitwise-AND operator compares each bit of its first operand to the corresponding
bit of its second operand. If both bits are 1, the corresponding result bit is set to 1. Otherwise,
the corresponding result bit is set to 0.
eg: 01001000 &
10111000 =
----------------
00001000
Bitwise OR(|)
The bitwise-inclusive-OR operator compares each bit of its first operand to the
corresponding bit of its second operand. If either bit is 1, the corresponding result bit is set to
1. Otherwise, the corresponding result bit is set to 0.
eg: 01001000 |
10111000 =
----------------
11111000

Bitwise XOR(^)

The bitwise-exclusive-OR operator compares each bit of its first operand to the
corresponding bit of its second operand. If one bit is 0 and the other bit is 1, the
corresponding result bit is set to 1. Otherwise, the corresponding result bit is set to 0.

eg: 01110010 ^
10101010
-------------
11011000

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Bitwise COMPLEMENT(~)
The ~ (tilde) operator performs a bitwise complement on its single integer operand
(unary operator), which inverts all the bits represented by its operand.ie,0s become 1s and 1s
become 0s,
Eg: x= 1001 0110 1100 1011
~x= 0110 1001 0011 0100

Bitwise Left Shift(<<)

Format is: op<<n
where op is the integer expression that is to be shifted and n is the number of bit positions to
be shifted.
The left-shift operation causes all the bits in the operand op to be shifted to the left by „n‟
positions by removing n bits from the left side of integer and adding n „0‟s to the right side.
Eg: x= 1001 0110 1100 1011
x<<4= 0110 1100 1011 0000
Bitwise Right Shift(>>)
Format is: op>>n
where op is the integer expression that is to be shifted and n is the number of bit positions to
be shifted.
The right-shift operation causes all the bits in the operand op to be shifted to the right by „n‟
positions by removing n bits from the right side of integer and adding n „0‟s to the left side.
Eg: x= 1001 0110 1100 1011
x>>4=0000 1001 0110 1100

8. Special Operators
C supports some special operators of interest such as comma operator, size of operator,
pointer operators (& and *) and member selection operators (. and ->). The size of and the
comma operators are discussed here. The remaining operators are discussed in forth coming
chapters.
1.The Comma Operator
The comma operator can be used to link related expressions together. Comma-linked, lists
of expressions are evaluated left to right and value of right most expression is the value of the
combined expression.
For example the statement
value = (x = 10, y = 5, x + y);
First assigns 10 to x and 5 to y and finally assigns 15 to value. Since comma has the lowest
precedence in operators the parenthesis is necessary. Some examples of comma operator are
In for loops:
for (n=1, m=10, n <=m; n++,m++)
In while loops
while (c=getchar(), c != „10‟)
Exchanging values
t = x, x = y, y = t;

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2.The size of Operator

The operator size of gives the size of the data type or variable in terms of bytes occupied in
the memory. The operand may be a variable, a constant or a data type qualifier.

Example
m = sizeof (sum);
n = sizeof (long int);
k = sizeof (235L);
The size of operator is normally used to determine the lengths of arrays and structures when
their sizes are not known to the programmer. It is also used to allocate memory space
dynamically to variables during the execution of the program.
Example program that employs different kinds of operators. The results of their evaluation
are also shown in comparison
main()
{ //start of program
int a, b, c, d; //declaration of variables
a = 15; b = 10; c = ++a-b; //assign values to variables
printf (“a = %d, b = %d, c = %d\n”, a,b,c); //print the values
d=b++ + a;
printf (“a = %d, b = %d, d = %d\n, a,b,d);
printf (“a / b = %d\n, a / b);
printf (“a %% b = %d\n, a % b);
printf (“a *= b = %d\n, a *= b);
printf (“%d\n, (c > d) ? 1 : 0 );
printf (“%d\n, (c < d) ? 1 : 0 );
}
Notice the way the increment operator ++ works when used in an expression. In the
statement c = ++a – b; new value a = 16 is used thus giving value 6 to C. That is a is
incremented by 1 before using in expression. However in the statement d = b++ + a; the old
value b = 10 is used in the expression. Here b is incremented after it is used in the expression.
We can print the character % by placing it immediately after another % character in the
control string.
This is illustrated by the statement.
printf(“a %% b = %d\n”, a%b);
This program also illustrates that the expression
c>d?1:0
Assumes the value 0 when c is less than d and 1 when c is greater than d.
2.2 TYPE CONVERSIONS IN EXPRESSIONS
2.2.1 IMPLICIT TYPE CONVERSION:
C permits mixing of constants and variables of different types in an expression. C
automatically converts any intermediate values to the proper type so that the expression can
be evaluated without losing any significance. This automatic type conversion is known as
implicit type conversion.
During evaluation it adheres to very strict rules and type conversion. If the operands
are of different types the lower type is automatically converted to the higher type before the
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operation proceeds. The result is of higher type. The following rules apply during evaluating
expressions: All short and char are automatically converted to int then
1.If one operand is long double, the other will be converted to long double and result will
be long double.
2.If one operand is double, the other will be converted to double and result will be
double.
3. If one operand is float, the other will be converted to float and result will be float.
4. If one of the operand is unsigned long int, the other will be converted into unsigned
long int and result will be unsigned long int.
5. If one operand is long int and other is unsigned int then
a). If unsigned int can be converted to long int, then unsigned int operand will
be converted as such and the result will be long int.
b). Else both operands will be converted to unsigned long int and the result will
be unsigned long int.
6. If one of the operand is long int, the other will be converted to long int and the result
will be long int.
7. If one operand is unsigned int the other will be converted to unsigned int and the
result will be unsigned int.

2.2.2 EXPLICIT CONVERSION:

Many times there may arise a situation where we want to force a type conversion in a way
that is different from automatic conversion.
Consider for example the calculation of number of female and male students in a class.
Female students
Ratio =
Male students
Since if female students and male students are declared as integers, the decimal part
will be rounded off and its ratio will represent a wrong figure. This problem can be solved by
converting locally one of the variables to the floating point as shown below.
Ratio = (float) female students / male students;
The operator float converts the female students to floating point for the purpose of
evaluation of the expression. Then using the rule of automatic conversion, the division is
performed by floating point mode, thus retaining the fractional part of the result. The process
of such a local conversion is known as explicit conversion or coasting a value. The general
form is,
(type_name) expression;

2.3 LIBRARY FUCNTIONS

Library functions carry out various commonly used operations or calculations. Some
functions return a data item to their access point, others indicate whether a condition is true or
false by returning 1 or0 respectively, still others carry out specific operations on data items
but do not return anything. Features which tend to be computer dependent are generally
written as library functions. Functionally similar library functions are usually grouped
together as object programs in separate library files. These library files are supplied as a part

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of each C compiler.
A library function is accessed simply by writing the function name, followed by a list
of arguments that represent information being passed to the function. The arguments must be
enclosed in parentheses and separated by commas. The arguments can be constants,variable
names or more complex expressions. The parentheses must be present, even if there are no
arguments, A function that returns a data item can appear anywhere within an expression in
place of a constant or an identifier. A function that carries out operations on data items but
does not return anything can be accessed simply by writing the function name, since this type
of function reference constitutes an expression statement.
In order to use a library function it may be necessary to include certain specific
information within the main portion of the program. This information is generally stored in
special files supplied with the compiler. Thus, the required information can be obtained
simply by accessing these special files. This is accomplished with the preprocessor statement.

# include <filename>

The list of some commonly used library functions are:

abs(i) to determine absolute value of i.

exp(i) raise e to the power i.

log(d) determine natural logarithm of d.

pow(d1,d2) returns d1 raised to the d2 power

putchar(c) send a character to the standard output device

sqrt(d) return the square root of d.

2.4 DATA INPUT AND OUTPUT STATEMENTS

In any programming language, the interface forms a very important part. It deals with
taking data from the user and displaying back the output. For this purpose, we require the
input-output operations.
Reading, processing, and writing of data are the three essential functions of a
computer program. The input operation involves movement of data from an input device to
computer memory, while in output operation the data moves from memory to output device
(generally screen).
In C the input and output is performed through a set of library functions that are
supplied with every C compiler. The set of library functions that perform input-output
operations is known as standard I/O library.
There are several header files that provide necessary information in support of various
library functions. These header files are included in the program using #include directive at
the beginning of the program. Each program that uses a standard input/output function must
contain the statement “#include <stdio.h>” at the beginning. However, there might be
exceptions. For example, this is not necessary for the functions printf and scanf which have
been defined as part of the C language.

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The file name stdio.h is an abbreviation for standard input -output header file. The
instruction #include <stdio.h> tells the compiler to search for a file named stdio.h and place
its contents at this point in the program. The contents of the header file become part of the
source code when it is compiled.
2.4.1 Single character input output:
The simplest of all input/output operations is reading a character from the standard
input unit (usually the keyboard) and writing it to the standard output unit (usually the
screen). Reading a single character can be done by using the function getchar. The getchar
takes the following form:
variable_name = getchar();
variable_name is a valid C name that has been declared as char type. When this
statement is encountered, the computer waits until a key is pressed and then assigns this
character as a value to getchar function. Since getchar is used on the right-hand side of an
assignment statement, the character value of getchar is in turn assigned to the variable name
on the left.
Example:
char name;
name = getchar();
Will assign the character 'H' to the variable name when we press the key H on the
keyboard. Since getchar is a function, it requires a set of parentheses as shown.
The putchar function which in analogous to getchar function can be used for writing
characters one at a time to the output terminal. The general form is
putchar (variable name);
Where variable is a valid C type variable that has already been declared
Example:
putchar ( c);
Displays the value stored in variable C to the standard screen.
Program shows the use of getchar function in an interactive environment.
#include < stdio.h > // Inserts stdio.h header file into the Pgm
void main ( ) // Beginning of main function.
{
char in; // character declaration of variable in.
printf (” please enter one character”); // message to user
in = getchar ( ) ; // assign the keyboard input value to in.
putchar (in); // out put „in‟ value to standard screen.
}

C supports testing of the character keyed in by the user by including the file ctype.h &
the functions which can be used after including this file are:
isalnum(c) Is c an alphanumeric character?
isalpha(c) Is c an alphabetic character?
isdigit(c) Is c a digit?
islower(c)Is c a lower case character?
isprint(c)Is c a printable character?

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ispunct(c)Is c a punctuation mark?

isspace(c)Is c a white space character?
isupper(c) Is c a upper case character?

2.4.2 String input and output:

The gets function recieves the string from standard input device while puts outputs the
string to the standard output device. A string is an array or set of characters. The function gets
accepts the name of the string as a parameter, and fills the string with characters that are input
from the keyboard till newline character is encountered. (That is till we press the enter key).
The puts function displays the contents stored in its parameter on the standard screen.
The standard form of the gets function is
gets (str);
Here str is a string variable.
The standard form for the puts character is
puts (str);
Where str is a string variable. The above statement will display the value stored in str on the
output device
Eample program (Involving both gets and puts)
# include < stdio.h >
void main ( )
{
char s [80];
printf (“Type a string less than 80 characters:”);
gets (s);
printf (“The string types is:”);
puts(s);
}
2.4.3 Formatted Input
Formatted input refers to an input data that has been arranged in a particular format.
For example, consider the following data:
15.73 123 John
This line contains three pieces of data, arranged in a particular form. Such data has to be read
conforming to the format of its appearance. For example, the first part of the data should be
read into a variable float, the second into int, and the third part into char. This is possible in C
using the scanf function.
The general form of scanf is
scanf("control string", arg1, arg2,......argn);
The control string specifies the field format in which the data is to be entered and the
arguments arg1, arg2,.....argn specify the address of locations where the data is stored .
Control string and arguments are separated by commas.
Control string consist of:
 Field specifications-Consists of conversion character %,data type character and an
optional number specifying field width
 blanks tabs or new lines

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Note; Data type character indicates type of data that is to be assigned to the variable
associated with corresponding argument
Inputting Integer Numbers
The field specification for reading an integer number is:
%wd
The percent (%) indicates a conversion specification follows.
w - integer number that specifies the field width of the number to be read and
d-known as data type character, indicates that the number to be read is in integer mode
eg: scanf(“%2d %5d”,&num1,&num2);
50 31246
Here 50 is assigned to num1 and 31246 is assigned to num2
If input data was 31426 and 50
31 is assigned to num1(since field width mentioned is 2) and
426 is assigned to num2
value 50 that is unread will be assigned to first variable in next scanf call.
These type of errors can be eliminated if we use field specification without field width.
Points to be noted:
 input data items should be separated by spaces tabs or newlines. When scanf searches
input data line for a value to be read, it will always bypass white space characters.
 input field may be skipped by specifying * in place of field width
eg: scanf(“%d%*d%d”,&a,&b);
let the input data be 123 456 789
Here 123 is assigned to a
456 is skipped(because of *)
789 to b
Inputting Real Numbers
Unlike integers numbers , the field width of real numbers is not to be specified and
therefore scanf reads real numbers using the simple specification %f for both the notations,
namely, decimal point notation and exponential notation. For example, the statement
scanf("%f %f %f , &x, &y , &z);
with the input data
472.34 43.21E-1 678
will assign the value 472.34 to x, 4.321 to y, and 678.0 to z. The input field
specifications may be separated by any arbitrary blank spaces.
Inputting Character Strings
We have already seen how a single character can be read from the terminal using the
getchar function. The same can be achieved using the scanf function also. In addition, a scanf
function can input strings containing more than one character strings:
%ws or %wc
The corresponding argument should be a pointer to a character array. However %c
may be used to read a single character when the argument is a pointer to a char variable.
Some versions of scanf supports the following conversion specification for strings
%[characters]
%[^characters]

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The specification %[characters] means that only the character specified within the
brackets are permissible in the input string. If the input string contains any other character the
string will be terminated at the first encounter. of such a character,
The specification %[^characters] does exactly the reverse. That is, the characters
specified after the (^) are not permitted in the input string. The reading of the string will be
terminated at the encounter of one of these characters.
Reading Mixed Data Types
It is possible to use one scanf statement to input a data line containing mixed mode
data. In such cases care should be given to ensure that input data items match the control
specifications in order and type. When an attempt is made to read an item that doesn‟t match
the type expected the scanf function doesn‟t read any further and immediately returns the
value read.
eg;scanf(“%d%c%f%s”,&count,&code,&ratio,name);
will read data 15 p 1,24 xyz
correctly and assign the values to variables in the order in which they appear.

scanf Format Codes:

%c reads a single character
%d read a decimal integer
%e read a floating point value
%f read a floating point value
%g read a floating point value
%h read a short integer
%i read a decimal, hexadecimal, or octal integer
%o read an octal integer
%s read a string
%u read an unsigned decimal integer
%x read a hexadecimal integer
%[..] read a string of word(s)
The following letters may be used as prefixes for certain conversion character
h for short integers
l for long integers or doubles
L for long double

2.4.4Formatted Output
Printf() is a versatile function. It can handle any basic data type, that offers several
features with which you can specify the way in which data must be displayed.
printf() performs formatted o/p to standard o/p device. It provides features that can be
used to control the alignment and spacing of print-outs on terminals.
printf(“control string”,arg1.arg2,…argn);
Control string consists of 3 types of items:
1. Characters that will be printed on the screen as they appear
2. format specifications that define the o/p format for display of each item
3. escape sequence characters such as \n,\t and \b.

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The control string indicates how many arguments follow and what their types are. The
arguments arg1,arg2..argn are the variables whose values are formatted and printed according
to the specifications of the control string. The arguments should match in number, order and
type with format specifications. A simple format specification has the following form:
%w.p type-specifier
where w is an integer number that specifies the total number of columns for the output
value and p is another integer number that specifies the number of digits to the right of the
decimal point or the number of characters to be printed from a string.Both w and p are
optional.
Output of Integer Numbers
The format specification for printing an integer number is:
%wd
where w specifies the minimum field width for the output. However if a number is greater
than the specified field width, it will be printed in full overriding the minimum specification.
d specifies that the value to be printed is an integer. The number will be printed right justified
in the given field width.
eg:printf(%6d”,9876); 9 8 6 7

Here the value is displayed right justified.

It is possible to force printing to be left-justified by placing minus sign directly after %
character
:printf(%-6d”,9876); 9 8 6 7

Output of Real Numbers

The output of a real number may be displayed in decimal notation by using the
following format specification:
%w.pf
The integer w indicates the minimum number of positions that are to be used for the display
of value and the integer p indicates the no:of digits to be displayed after decimal point
(precision).The default precision is 6 decimal places.
We can also display a real number in exponential notation by using the specification:
%w.pe
The field width w should satisfy the condition w>=p+7
The display takes the form: [-]m.nnnne[+-]xx
eg: let y=-98.7654
printf(“%11.4e”,y) will display - 9 . 8 7 6 5 e + 0 1

Specifier Meaning
%c – Print a character
%d – Print a Integer
%i – Print a Integer
%e – Print float value in exponential form.
%f – Print float value
%g – Print using %e or %f whichever is smaller
%o – Print actual value
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%s – Print a string
%x – Print a hexadecimal integer (Unsigned) using lower case a – F
%X – Print a hexadecimal integer (Unsigned) using upper case A – F
%a – Print a unsigned integer.
%p – Print a pointer value
%hx – hex short
%lo – octal long
%ld – long
2.5 CONTROL STATEMENT: BRANCHING
A C program is a set of statements which are normally executed sequentially in the
order in which they appear. This happens when no options or no repetitions of certain
calculations are necessary. However there are a number of situations in which we need to
change the order of execution of statements based on certain conditions, or repeat a group of
statements until certain specified conditions are met. This involves a kind of decision making
to see whether a particular condition has occurred or not and then direct the computer to
execute certain statements accordingly.
C language posses such decision-making capabilities by supporting the following statements:
1.If statement
2.switch statement
3.Conditional operator statement
4.goto statement.

2.5.1 Decision Making with IF Statement

The if statement is a powerful decision-making statement and is used to control the flow
of execution of statements. It is basically a two-way decision statement and is used in
conjunction with an expression. It takes the following form:
if(test expression)
It allows the computer to evaluate the expression first and then depending on whether the
expression is true or false, it transfers the control to a particular statement. This point of
program has two paths to follow, one for the true condition and other for the false condition.

Entry

False
test exp
?
True

fig 2.1
2.5.1.1 SIMPLE IF STATEMENT
The general form of simple if statement is
if (test expression)
{
statement-block; ;
}
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statement-x;
The „statement-block‟ may be a single statement or a group of statements. If the test
expression is true, the statement-block will be executed; otherwise the statement-block will
be skipped and execution will jump to statement-x .If the condition is true both statement-
block and statement-x are executed in sequence.

True
Test exp

statement-block
False
False

statement-x

next statement

fig 2.2
Example:
------------------------
if (category==”sports”)
{
marks=marks+bonus_marks;
}
printf(“%f”,marks);
………………….

2.5.1.2 IF ELSE STATEMENT

if (test expression)
{
True-block statement ;
}
else
{
False-block statement;
}
statement-x;

If the test expression is true then the true-block statements immediately following the if
statements are executed. Otherwise the false-block statements are executed. In either

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case,either true -block or false-block will be executed, not both. In both cases, the control is
transferred to statement-x.
eg:
…………..
……………
if(code==1)
boy=boy+1;
else
girl=girl+1;
………………

true false
test exp

true-block stmts false-block stmts

statement x

fig 2.3
2.5.1.3 NESTING OF IF …ELSE STATEMENTS
When a series of decisions are involved, we may have to use more than one if …else
statement in nested form as follows:
if(test condition1)
{
if (test condition 2)
{
Statement 1;
}
else
{
Statement 2;
}
}
else
{
Statement 3;
}
Statement x;
eg:
……………….
if(sex ==”female”)
{
if(balance>5000)

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bonus=.05*balance;
else
bonus=.02*balance;
}
else
{
bonus=.01*balance;
}
balance=balance+ bonus;
………………………..
The logic of execution is in figure. If the condition1 is false, the statement3 will be
executed; otherwise it continues to perform the second test. If the condition 2 is true, the
statement1 will be evaluated; otherwise the statement2 will be evaluated and then the control
is transferred to the statement x.
Entry

False
Test True

Condition 1

False Test
Statement3
Condition 2
Statement2 Statement1

True

Statement x

Next
Statement
(Fig: 2.4)

2.5.1.4 The ELSE IF LADDER

There is another way of putting ifs together when multipath decisions are involved. A
multipath decision is a chain of ifs in which the statement associated with each else is an if. It
takes the following general form:
if (condition 1)
{
Statement 1;
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}
else if(condition 2)
{
Statement 2;
……….
}
else if(condition n)
{
Statement n;
}
else
default statement;

Statement x;
The conditions are evaluated from the top (of the ladder), downwards. As soon as a
true condition is found, the statement associated with it is executed and the control is
transferred to the statement-x (skipping the rest of the ladder). When all the n conditions
become false, then the final else containing the default-statement will be executed.

entry

true
false
cond1

true false
stmt 1
cond2

stmt 2 true false

cond3

true false
stmt 3
condn

stmt n default stmt

stmt -x

next stmt

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fig 2.5

2.5.2.1 SWITCH STATEMENT

When one of the many alternatives is to be selected, we can use an if statement to
control the selection. However the complexity of such a program increases when the number
of alternative increases. The program becomes difficult to read and follow. In C there is a
built-in multi way decision statement known as switch. The switch tests the value of a
variable(or expression) against a list of case values and when a match is found ,block of
statements associated with that case is executed.

Syntax :-
switch(expression)
{
case value-1:
block-1
break;
case value-2:
block-2
break;
----------
----------
default:
default-block
break;
}
statement x;
The expression is an integer expression or characters.Value-1,value-2…are constants
or constant expressions and are known as case labels. Each of these values should be unique
within a switch statement.block-1,block-2.. are statement lists and may contain zero or more
statements. There is no need to put braces around these blocks. Note that case labels end with
a colon(:).
When the switch is executed, the value of the expression is compared against the
values of Value-1,value-2…If a case is found whose values match with the value of the
expression, then the block of statements that follows the case are executed.
The break statement at the end of each block signals the end of a particular case and
causes an exit from the switch statement, transferring the control to the statement following
the switch.
The default is an optional case. When present, it will be executed if the value of the
expression doesn‟t match with any of the case values. If not present no action takes place if
all matches fail and the control goes to the statement-x.
eg:
switch(c)
{
case „+‟ : printf(“Enter the values for a & b\n”);
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scanf(“%d %d”,&a,&b);
printf(“a + b = %d\n”,a+b);
break;
case „-‟ : printf(“Enter the values for a & b\n”);
scanf(“%d %d”,&a,&b);
printf(“a - b = %d\n”,a-b);
break;
case „*‟ : printf(“Enter the values for a & b\n”);
scanf(“%d %d”,&a,&b);
printf(“a * b = %d\n”,a*b);
break;
case „/‟ : printf(“Enter the values for a & b\n”);
scanf(“%d %d”,&a,&b);
printf(“a / b = %d\n”,a/b);
break;
default : printf(“Invalid operator\n”);
}
}
2.5.2.2 NESTED SWITCH () CASE
C supports the nested switch() statements. The inner switch() can be a part of an outer
switch().the inner and outer switch() case constants may be same. No conflict arises even if
they are same.
Program to detect whether the entered number is even or odd. Use nested switch() case
statements.
void main()
{
int x,y;
printf(“Enter a number”);
scanf(“%d”,&x);
switch(x)
{
case 0:
printf(“Number is even”);
break;
case 1:
printf(“Number is odd”);
break;
default:
y=x%2;
switch(y)
{
case 0:
printf(“Number is even”);
break;
default:
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printf(“Number is odd”);
}
}
}
THE SWITCH () CASE AND NESTED IFS
Switch() Nested ifs
The switch() can only test The if can evaluate relational or logical
for equality. only constant values are expressions
applicable.
No two case statements have identical Same conditions may be repeated for
Constants in the same switch Number of times.
Character constants are automatically Character constants are automatically converted
converted to integers to integers
In switch()case statement nested In nested if statement switch() case can be used
If can be used

(Table: 2.5)
2.5.3 THE GOTO STATEMENT
The goto statement is used to alter the normal sequence of program execution by
transferring control to some other part of the program. it is useful to provide branching within
a loop. It can be used to exit out of a loop also.
while(test-condition 1)
{
if(condition 2)
goto stop;

Jump -----------
within loop if(condition 3) Exit from
goto abc; loop
---------
abc:
-------
}
stop:

In its general form, the goto statement is written as

goto label;
Where label is an identifier that is used to label the target statement to which control
will be transferred.
Control may be transferred to any other statement within the program. The target
statement must be labeled, and the label must be followed by a colon. Thus the target
statement will appear as
label: statement
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Each labeled statement within the program must have a unique label; i.e., no two statements
can have the same label.
goto label; label:
statement;
-------------- --------------
-------------- --------------
label: goto label;
statement
Forward jump Backward jump

If the label: is before the statement goto label; a loop will be formed and some
statements will be executed repeatedly. Such a jump is known as a backward jump. On the
other hand, if the label: is placed after the goto label; some statements will be skipped and the
jump is known as a forward jump.
A goto is often used at the end of a program to direct the control to go to the input
statement,to read further data.
Points to be remembered while using the goto statement:
 The use of goto statement in a structured programming language like C should be
avoided. Use if and only if it is unavoidable
 The goto statement may create an infinite loop where the computer enters a
permanent loop. The careful and cautious design would resolve such situations.
 A program may contain any number of goto statements.
 No two statements can have the same label.

goto jumps to be avoided

Write a C program to accept an integer number and reverse it?

void main()
{
int number, rev=0, digit,temp_num;
printf(“Enter a number\n”);
scanf(“%d”,&number);
temp_num=number;
START:
digit=number%10;
rev=rev*10+digit;
number/=10;
if (number>0)

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goto START;
printf(“Input number=%5d\n”,temp_num);
printf(“Reversw number=%5d\n”,rev);
}
Output
Enter a number
9876
Input number=9876
Reverse number=6789

2.6 DECISION MAKING AND LOOPING

In looping, sequences of statements are executed until some conditions for
termination of the loop are satisfied. A program loop therefore consists of two segments, one
known as the body of the loop and the other known as the control statement. The control
statement tests certain conditions and then directs the repeated execution of the statements
contained in the body of the loop.
Depending on the position of the control statement in the loop, a control structure
may be classified either as the entry-controlled loop or as the exit-controlled loop. In the
entry controlled loop, the control conditions are tested before the start of loop execution. If
the conditions are not satisfied, then the body of the loop will not be executed .In the case of
an exit-controlled loop, the test is performed at the end of the body of the loop and therefore
the body is executed unconditionally for the first time. The entry-controlled and exit –
controlled loops are also known as pre-test and post-test loops respectively.

A looping process, in general, would include the following four steps:

1. Setting and initialization of a condition variable
2. Execution of the statements in the loop
3. Test for a specified value of the condition variable for execution of the loop.
4. Incrementing or updating the condition variable

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The test may be either to determine whether the loop has been repeated the specified
number of times or to determine whether a particular condition has been met. The C language
provides for three constructs for performing loop operations.
They are:
1. The while statement
2. The do statement
3. The for statement
Based on the nature of control variable and the kind of value assigned to it for testing
the control expression, the loops may be classified into two general categories:
1 Counter-controlled loops
2 Sentinel-controlled loops

When we know in advance how many times a loop should be executed, we use
a counter controlled loop.We use a control variable called counter. The counter must be
initialized, tested and updated properly for desired loop operations.The no;of times the loop
should be executed may be constant or a variable that is assigned value. It is also called
definite repetition loop.
Eg: sum=0;
n=1;
while(n<=10)
{
sum=sum+n*n;
n=n+1;
}
Here this loop will be executed 10 times. The variable n is called counter or control variable.
In a Sentinel-Controlled loop, a special value called a sentinel value is used to
change the loop control expression from true to false. For example, when reading data we
may indicate the "end of data" by a special value, like -1 and 999. The control variable is
called sentinel variable. A sentinel-Controlled loop is often called indefinite repetition loop
because the number of repetitions is not known before the loop begins executing.
Eg: char character=‟‟;
while(character!=‟y‟)
{
character = getchar();
putchar(c);
}

Here the loop is executed as long as the key „y‟ is pressed. When „Y‟ is pressed the condition
becomes false the loop terminates and control transfers to the statement following the loop.
Here the value „Y‟ is called sentinel value and the variable „character‟ is called the sentinel
variable.

2.6 .1 WHILE STATEMENT

The simplest of all the c looping structures in C is the while statement. The while
statement is an entry-controlled loop statement. The test condition is evaluated and if the
condition is true then the body of the loop is executed. After the execution of the body the
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test condition is once again evaluated and if it is true, the body is executed once again. This
process of repeated execution of the body is continued until the test condition becomes false
and the control is transferred out of the loop. On exit the program is continued with the
statement after the body of the loop.
The body of the loop may have one or more statements. The braces are needed only if
the body contains two or more statements.
The format of while statement is
while (test condition)
{
body of the loop
}

Eg:
x = 10; ------------- Initialization
while (x < 16) ------------- Test condition
{
printf("%d",x); ------------- body of the loop
x = x+1;
}

Example:
# include<stdio.h>
main()
{
int count,n;
float x,y;
printf(“Enter the values of x and n:”);
scanf(“%f %d”, &x, &n);
y= 1.0;
count = 1;
/* LOOP BEGINS*/
while(count<= n)
{
y = y * n;
count ++;
}
/*End of loop*/
printf(“ x = %f ; n = %d ; to power n = %f n “, x , n, y);
}

2.6 .2 DO STATEMENT
The do while loop is also a kind of loop, which is similar to the while loop in contrast to
while loop, the do while loop tests at the bottom of the loop after executing the body of the
loop. Do is an exit-controlled loop. Since the body of the loop is executed first and then the

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loop condition is checked we can be assured that the body of the loop is executed at least
once.
The syntax of the do while loop is:
do
{
statement;
}
while(expression);
Here the statement is executed, then expression is evaluated. If the condition expression is
true then the body is executed again and this process continues till the conditional expression
becomes false. When the expression becomes false the loop terminates.
A while loop says "Loop while the condition is true, and execute this block of code", a
do..while loop says "Execute this block of code, and then continue to loop while the
condition is true".
Eg: void main()
{
int c;
do
{
printf(“enter number”);
scanf(“%d”,&c);
printf(“%d\n”,c);

} while (c>0);
}

Here the loop is executed at least once. Even if we are entering a value less than 0 at first
time itself, the loop will be executed once and then terminates. Or else the loop will be
iterated as long as the value of c is greater than 0

2.6.3 FOR LOOP

Syntax:
for (initialization ; test ; increment)
{
statements ;
}
Program flow
1.The initialization of control variable is done first,using assignment statements like int i=0
or count=0.The variables i and count are called loop control variable.
int i=0,which creates a new variable with initial value 0, to act as a counter. Multiple,
comma separated, expressions are allowed in the initialization section. But declaration
expressions may not be mixed with other expressions.

2.Value of the control variable is evaluated using test condition. It is a relational expression
like i<0 that determines when the loop will exit. If condition is true, body of the loop is
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executed, Otherwise loop is terminated and execution will continue with statement that
immediately follow the loop.

3.When the body of the loop is executed, the control is transferred back to the for
statement after evaluating last statement in loop control. Now the control variable is
incremented using assignment statement such as i=i+1 and the new value is tested to
check whether it satisfies the test condition. If condition is satisfied body of the loop will
be again executed. This process continues till value of control variable fails to satisfy test
condition.

eg:
for(x=0;x<10;x=x+1)
{
printf(“%d\n”,x);
}

Here loop will be executed 10 times and the digits 0 to 9 will be printed. The 3 sections
should be separated by semicolon.

for statement allows negative increment also

eg:
for(x=9;x>0;x=x-1)
{
printf(“%d\n”,x);
}
Here loop will be executed 10 times and the digits 9 to 0 will be printed.
Since we are checking condition at the beginning of loop, the body of loop may not be
executed if the condition fails at the start.
eg:
for(x=9;x<9;x=x-1)
{
printf(“%d\n”,x);
}
The above loop will never be executed.

In for statement, initialization, testing and incrementing are placed in for statement itself
making it visible to programmers and users in one place.

Additional Features

 More than one variable can be initialized and incremented at a time in a for loop.
for(n=1,m=50;n<=m;n=n+1,m=m-1)
{
p=m/n;
}

 The test-condition may have any compound relation and the testing need not be limited
only to the loop control variable.
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Eg: for(i=1;i<20 && sum<100;i++)

{
sum=sum+i;
printf(“%d%d”,i,sum);
}

 It is permissible to use expressions in the assignment statements of initialization and

increment sections.
Eg:

for(x=(m+n)/2;x>0;x=x/2)

 One or more sections of the for loop can be omitted ,if necessary
Eg: m=0;
for(; m<100;)
{
printf(“%d”,m);
m=m+5;
}

 We can set up time delay loops using for statement

Eg: for(j=0;j<1000;j++);
Here the semi colon at the end is known as null statement. Here the loop will be
executed 1000 times without executing any output.

 It is possible to use a scanf statement in for statement to assign value to the control
variable
Eg:for(scanf(“%d”,&n);n>0;n=n/2)

2.6.3.1 Nested for loops

In some cases a set of statements which are repeated for a known number of times need to
be executed as long as a condition holds. In such case we will enclose this loop in another
loop. The enclosing loop is called Outer loop and the enclosed loop is called Inner loop.

for (i=0;i<5;i++)
Outer Loop
{
--------
----------- Inner Loop
for(j=0;j<3;j++)
{
---------
----------
}

Eg:Multiplication tables of a range of numbers

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# include<stdio.h>
main ()
{
int m,n,i,j,p;
printf(“enter the lower limit and upper limit\n”);
scanf(“%d%d”,&m,&n);
for(i=m;i<=n;i++)
{
for(j=1;j<=10;j++)
{
p=i*j;
printf(“%d”,p);
printf(“”);
}
printf(“\n”);
}
}

We need to generate multiplication table of the given range of numbers. So we need

to nest one loop within another. The outer loop is to select each number in the range and the
inner loop is to generate the multiplication table of the number selected by the outer loop.
In the outer loop when i takes m, the lower limit, the inner loop generates the
multiplication table of m. Once the inner loop completes, control goes to the outer loop
again.i gets incremented it becomes m+1.Then inner loop generates the multiplication table
of m+1>this continues as long as the test condition of outer loop is true.

2.7 BREAK AND CONTINUE STATEMENTS

C provides two commands to control how we loop

1. break
2. continue

2.7.1.1 The Break Statement:

The statements in a loop will be executed continuously as long as the test expression
is true. Sometimes while executing a loop it becomes desirable to skip a part of the loop or
quit the loop as soon as certain condition occurs. For example consider searching a particular
number in a set of 100 numbers as soon as the search number is found it is desirable to
terminate the loop. C language permits a jump from one statement to another within a loop as
well as to jump out of the loop. The break statement allows us to accomplish this task. A
break statement provides an early exit from for, while, do and switch constructs. A break
causes the innermost enclosing loop or switch to be exited immediately.

A break statement used within a loop is expected to be associated with an if statement.

When the test expression of if statement evaluates to true, the loop is exited prematurely.
while(test-expression 1)

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{
Statements-1;
If (test-expression 2)
break;
Statements-2;
}

During the course of iteration if the test expression-2 evaluates to true, The control reaches
the break statement and executes it causing the loop to be exited prematurely.
Eg:# include<stdio.h>
main()
{
int n,i,sum=0,number;
printf(“enter no;of elements\n”);
scanf(%d‟,&n);
printf(“enter numbers\n”);
for(i=1;i<=n;i++)
{
scanf(“%d”,& number);
if(number<0)
break;
sum=sum+number;
}
printf(“sum of %d positive numbers=%d”,i-1,sum)
}
Here in the course of accepting numbers, if the positive numbers are entered, they are
added to the variable sum. But if a negative number is entered, then control reaches the break
statement, which, when executed causes the loop to be executed prematurely. The value of
sum is then displayed.
2.7.1.2Break in nested for loops

In nested loops the break statement affects only the loop in which it is enclosed.
for(initialization1;test-condition1;increment1)
{
for(initialization2;test-condition2;increment2)
{
if(test-condition3)
break;
}

Statements;
}

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Here on encountering break statement control will exit out of the inner for loop and
continue with the statements outside the inner loop.

for(initialization1;test-condition1;increment1)
{
for(initialization2;test-condition2;increment2)
{
Statements- 2;
}
if(test-condition3)

break;
}

Statements;

Here the break statement is enclosed in the outer for loop. On encountering the break
statement the control will exit out of outer for loop.
2.7.2.1Continue statement:

During loop operations it may be necessary to skip a part of the body of the loop
under certain conditions. Like the break statement C supports similar statement called
continue statement. The continue statement causes the loop to be continued with the next
iteration after skipping any statement in between. The format of the continue statement is
simply:
continue;
Similar to the break statement ,continue statement is also associated with an if statement.
While(test-expression 1)
{
Statements-1;
if (test-expression 2)
continue;
Statements-2;
}
During the course of iteration if the test expression-2 evaluates to true, the control
reaches the continue statement ,the statement-2 are skipped for those iterations and the
control goes to the beginning of the loop. The loop is not prematurely exited as in the case of
break statement
Eg:# include<stdio.h>
main()
{
int n,i,sum=0,number;
printf(“enter no;of elements\n”);
scanf(%d‟,&n);

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Module 2 MCA-105 Structured Programming in C ADMN 2011-‘14

printf(“enter numbers\n”);
for(i=1;i<=n;i++)
{
scanf(“%d”,& number);
if(number<0)
continue;
sum=sum+number;
}
printf(“sum of %d positive numbers=%d”,i-1,sum);
}

Here in the course of accepting numbers, if the positive numbers are entered, they are
added to the variable sum. But if a negative number is entered, then control reaches the
continue statement, which, when executed, causes the skipping of the statements following it
within in the loop and causes the control to be transferred back to the beginning of the loop,
so that the loop continues with the next iteration.

2.7.2.2 Continue in nested loops

for(initialization1;test-condition1;increment1)
{
for(initialization2;test-condition2;increment2)
{
if(test-condition3)
continue;
}
Statements;
}

Here when test-condition 3 is true the continue statement is encountered control is

transferred to the next iteration of inner for loop skipping all the statements following
continue in inner loop.

for(initialization1;test-condition1;increment1)
{
for(initialization2;test-condition2;increment2)
{
Statements- 2;
}
if(test-condition3)
continue;
}
Statements;

Dept of Computer Science And Applications, SJCET, Palai 61

Module 2 MCA-105 Structured Programming in C ADMN 2011-‘14

Differences between break and continue

Break Continue

Can be used in switch statement Cannot be used in switch statement

Causes premature exit of the loop Causes skipping of the statements

enclosing it following it in the body of the loop

The control is transferred to the Control is transferred back to the loop

statement following the loop

The loop may not complete the The loop completes the intended
intended number of iterations number of iterations.

2.8 EXIT FUNCTION()

Exit function is defined in header file <stdlib.h>

Just as you can break out of a loop, you can break out of a program by using the
standard library function exit(). This function causes immediate termination of the entire
program, forcing a return to the operating system. In effect, the exit() function acts as if it
were breaking out of the entire program.
The general form of the exit() function is
if(test-condition)
exit(int return_code);

Eg:
# include<stdio.h>
# include<conio.h>
void main()
{
int num1,num2,res;
while(1)
{
scanf("%d%d",&num1,&num2);
if(num2==0)
exit(0);
else
{
res=num1/num2;
printf("result of division is %d\n",res);
}
}
}

Usually in our programs we will use exit(0) which indicates a normal termination of program.

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