c programing language Chapter 05 - Control Structures.pdf

Dr. Niroj Kumar Pani nirojpani@gmail.com Department of Computer Science Engineering & Applications Indira Gandhi Institute of Technology Sarang, Odisha Control Structures Chapter 5

Chapter Outline… ◼ Introduction ◼ Decision Control Structure ➢ The if Statement ➢ The switch Statement (Multi Way Decision) ➢ Assignments - I ◼ Loop Control Structure ➢ Introduction ➢ The while Loop / Statement ➢ The do-while Loop / Statement ➢ The for Loop / Statement ➢ Nesting of Loops Dr. N. K. Pani, Dept. of CSEA, IGIT Sarang | 5.2

◼ Jump Control Structure (Unconditional Jump) ➢ Introduction ➢ The continue Statement ➢ The break, return, and exit() Statements ➢ The goto Statement ➢ Assignments - II Dr. N. K. Pani, Dept. of CSEA, IGIT Sarang | 5.3

Introduction ◼ Control structures defines the order in which the statements in a program are executed. ◼ There are four types of control structures in C: 1. Sequence control structure: ➢ Control flows in a straight line. ➢ All the statements in the program are executed one after another, starting from the 1st statement to the last statement. ➢ All the programs that we have done so far, fall into this category. 2. Selection / Decision / Branch control structure: ➢ A condition is examined. ➢ A statement (or a group of statements) is executed if the condition is true and another statement (or group of statements) is executed if the condition becomes false. Dr. N. K. Pani, Dept. of CSEA, IGIT Sarang | 5.4

➢ Implemented though the following statements / constructs: ▪ if statement. It has four different forms: − Simple if statement − if...else statement − Nested if...else statement − else if ladder ▪ switch statement 3. Loop / Repetition / Iteration control structure: ➢ A condition is examined. ➢ A statement (or a group of statements) is repeatedly executed till the condition is true. ➢ Implemented though the following statements / constructs: ▪ while statement. ▪ do...while statement ▪ for statement Dr. N. K. Pani, Dept. of CSEA, IGIT Sarang | 5.5

4. Jump control structure (Unconditional jump): ➢ We jump from one statement to another unconditionally. ➢ Implemented though the following statements / constructs: ▪ continue statement ▪ break statement ▪ return statement ▪ exit() statement ▪ goto statement. In the following sections, we shall discuss each of the control structures (except the sequence control structure) in detail. Dr. N. K. Pani, Dept. of CSEA, IGIT Sarang | 5.6

Selection / Decision / Branch Control Structure

The if Statement Simple if (One-way decision) ◼ Syntax: ◼ Control Flow: ➢ The expression is evaluated 1st . ➢ If it is true (non-zero), the set of statements within the if block is executed (sequentially). The control is then transferred to statement immediately after the if block . ➢ If it is false (zero), the set of statements within the if block are skipped and the control is directly transferred to the statement immediately after the if block . if(expression) { statement(s); } if block Here, — expression corresponds to a C expression, that is evaluable to either true (non-zero) or false (zero). — statement(s) corresponds to a set of statements (0, 1, or more no. of statements). Dr. N. K. Pani, Dept. of CSEA, IGIT Sarang | 5.8

◼ Programming Example: /* PR5_1.c: Input four integers a, b, c, d and print the value of (a+b)/(c-d) if (c-d) ≠0 */ # include <stdio.h> # include <conio.h> void main() { int a, b, c, d; float result; printf("Enter four integers: "); scanf("%d %d %d %d", &a, &b, &c, &d); if((c-d)!=0) { result = (float)(a+b)/(c-d); printf("The value of (a+b)/(c-d) is: %f", result); } getch(); } Run 1: Enter four integers: 12 3 8 3 The value of (a+b)/(c-d) is: 3.000000 Run 2: Enter four integers: 12 3 8 8 Output Dr. N. K. Pani, Dept. of CSEA, IGIT Sarang | 5.9

◼ Notes: 1. When the if block contains just a single statement then the curly braces become optional. i.e., However, this programming style should be avoided. 2. Never put a semicolon (;) after the if clause , because it will be same as writing no statements within the if block. if(expression) { statement 1; } statement 2; if(expression) statement 1; statement 2; is same as if(expression); { statement 1; } statement 2; if(expression) ; /*A blank statement*/ statement 1; statement 2; is same as Dr. N. K. Pani, Dept. of CSEA, IGIT Sarang | 5.10

3. Suppose, in the expression your intension is to write x == 0, but by mistake you have written x = 0. i.e., Then what will happen? In this case, the statements within the if block are never executed, no matter whether x is equals to zero or not. Because, in C, 0 is always false. When we write x=0, x becomes false i.e., the total expression becomes false. So, be careful while writing x==0. if(x==0) { statement 1; statement 2; } if(x=0) { statement 1; statement 2; } is by mistake written as Dr. N. K. Pani, Dept. of CSEA, IGIT Sarang | 5.11

The if...else Statement (Two-way decision) ◼ The simple if statement does nothing when the expression becomes false. If we want to execute one set of statements when the condition (expression) becomes true and some other set of statements when the condition (expression) becomes false , then we should use the if...else statement. ◼ Syntax: if(expression) { statement(s); } else { statement(s); } if block else block Dr. N. K. Pani, Dept. of CSEA, IGIT Sarang | 5.12

◼ Control Flow: ➢ The expression is evaluated 1st . ➢ If it is true (non-zero), the set of statements within the if block is executed (sequentially). If it is false (zero), the set of statements within the else block is executed (sequentially). ➢ After the execution of the set of statements either in the if block or in the else block, the control is transferred to the statement immediately after the if...else construct (i.e., after the closing curly brace of the else block ). ◼ Notes: 1. When the else block contains just a single statement then the curly braces becomes optional. i.e., However, this programming style should be avoided. else { statement 1; } statement 2; else statement 1; statement 2; is same as Dr. N. K. Pani, Dept. of CSEA, IGIT Sarang | 5.13

◼ Programming Example 1: /* PR5_2.c: The same program as in PR5_1, but in this case, it will print “(c-d) = 0, The result is undetermined.”, if (c-d) becomes equal to 0 */ # include <stdio.h> # include <conio.h> void main() { int a, b, c, d; float result; printf("Enter four integers: "); scanf("%d %d %d %d", &a, &b, &c, &d); if((c-d)!=0) { result = (float)(a+b)/(c-d); printf("The value of (a+b)/(c-d) is: %f", result); } else { printf("(c-d) = 0, The result is undetermined."); } getch(); } Run 1: Enter four integers: 12 3 8 3 The value of (a+b)/(c-d) is: 3.000000 Run 2: Enter four integers: 12 3 8 8 (c-d) = 0, The result is undetermined. Output Dr. N. K. Pani, Dept. of CSEA, IGIT Sarang | 5.14

◼ Programming Example 2: /* PR5_3.c: Program to enter an integer and check whether it is even or odd*/ # include <stdio.h> # include <conio.h> void main() { int a; printf("Enter an integer: "); scanf("%d", &a); if(a%2 == 0) { printf("n%d is an even integer.", a); } else { printf("n%d is an odd integer.", a); } getch(); } Run 1: Enter an integer: 12 12 is an even integer. Run 2: Enter an integer: 5 5 is an even integer. Output Dr. N. K. Pani, Dept. of CSEA, IGIT Sarang | 5.15

The Nested if...else Statement (Multi way decision) ◼ When we put an entire if statement or an entire if...else statement within the if block or the else block or both of another if...else statement, then the construct is called nested if...else. ◼ Syntaxes: if(expression1) { statement(s); if(expression2) { statement(s); } else { statement(s); } statement(s); } if(expression1) { if(expression2) { statement(s); } } else { if(expression3) { statement(s); } else { statement(s); } statement(s); } Dr. N. K. Pani, Dept. of CSEA, IGIT Sarang | 5.16

◼ Programming Example: /* PR5_4.c: Program to find the largest among three integers*/ # include <stdio.h> # include <conio.h> void main() { int a, b, c, largest; printf("Enter three integers: "); scanf("%d %d %d", &a, &b, &c); if(a>b) { if (a>c) largest = a; else largest = c; } else { if (c>b) largest = c; else largest = b; } [Cont.] Dr. N. K. Pani, Dept. of CSEA, IGIT Sarang | 5.17

◼ Notes: 1. Dangling Else Problem: While nesting, care should be exercised to match every else statement with an if statement. When an else statement has no matching if, then that else is called dangling else. printf("nThe largest number is: %d", largest); getch(); } Enter three integers: 12 15 2 The largest number is: 15 Output if() if() if() else else else else /* The dangling else*/ Dr. N. K. Pani, Dept. of CSEA, IGIT Sarang | 5.18

2. How to know which else belongs to (matches to) which if?: The answer is simple. An else is always matched with the nearest unmatched if. if() if() if() else /*Belongs to the if() in line no. 3*/ else /*Belongs to the if() in line no. 2*/ else /*Belongs to the if() in line no. 1*/ if() else /*Belongs to the if() in line no. 7*/ if() else /*Belongs to the if() in line no. 9*/ else /*Dangling else*/ 1 2 3 4 5 6 7 8 9 10 11 Dr. N. K. Pani, Dept. of CSEA, IGIT Sarang | 5.19

3. Try to avoid nested if...else statements unless until it is highly required. There are two reasons for it: i. Nested if...else statements are complex to understand and handle. ii. Almost all the programs that requires nested if...else construct, can also be easily done with the else if ladder. We will discuss the else if ladder next. We will see that the program (PR5_4.c) that we have done by using the if...else construct, can be done very easily with the else if ladder . Dr. N. K. Pani, Dept. of CSEA, IGIT Sarang | 5.20

The else if Ladder (Multi-way decision) ◼ The else if ladder does the same thing as that of the nested if...else construct (both are meant for multi way decision making), but in a simpler manner. ◼ Syntax: if(expression1) { statement(s); } else if(expression2) { statement(s); } else if(expression3) { statement(s); } else { statement(s); } The total structure contains only one if at the beginning, and only one else at the end. Dr. N. K. Pani, Dept. of CSEA, IGIT Sarang | 5.21

◼ Control Flow: ➢ The expressions are evaluated from the top (of the ladder), downwards. ➢ As soon as an expression is found to be true, the block of statements associated with that expression is executed (no other statement block is executed). ➢ If all the expressions are evaluated to be false, then the final else statement is executed. ➢ After the execution of any one block of statements present in the ladder (either the if block, or any one of the else if blocks, or the final else block), the control is transferred to the statement immediately after else if ladder (skipping the rest of the ladder). Dr. N. K. Pani, Dept. of CSEA, IGIT Sarang | 5.22

◼ Programming Example 1: /* PR5_5.c: The same program as that of PR5_4.c (Program to find the highest among three integers), using else if ladder*/ # include <stdio.h> # include <conio.h> void main() { int a, b, c, greatest; printf("Enter three integers: "); scanf("%d %d %d", &a, &b, &c); if(a>b && a>c) greatest = a; else if(b>a && b>c) greatest = b; else greatest = c; printf("nThe greatest number is: %d", greatest); getch(); } Enter three integers: 12 15 2 The greatest number is: 15 Output Dr. N. K. Pani, Dept. of CSEA, IGIT Sarang | 5.23

◼ Programming Example 2: An electric power distribution company charges its domestic consumers as follows: Consumption Units Rate of Charge 0 - 200 Rs. 0.50 per unit 201 - 400 Rs. 100 plus Rs.0.65 per unit excess of 200 401 - 600 Rs. 230 plus Rs.0.80 per unit excess of 400 601 and above Rs. 390 plus Rs.1.00 per unit excess of 600 Write a program that reads the customer number and power consumed and prints the amount to be paid by the customer. Dr. N. K. Pani, Dept. of CSEA, IGIT Sarang | 5.24

/* PR5_6.c: Electricity Bill Estimation */ # include <stdio.h> # include <conio.h> void main() { int units, custNo; float chrges; printf("Enter CUSTOMER NO. & UNITS consumed: "); scanf("%d %d", &custNo, &units); if (units <= 200) chrges = 0.5 * units; else if (units <= 400) chrges = 100 + 0.65 * (units - 200); else if (units <= 600) chrges = 230 + 0.8 * (units - 400); else chrges = 390 + (units - 600); printf("nCustomer No: %d, Charges = %.2fn", custNo, chrges); getch(); } Enter CUSTOMER NO. & UNITS consumed: 11 340 Customer No: 11, Charges = 358.00 Output Dr. N. K. Pani, Dept. of CSEA, IGIT Sarang | 5.25

[NOTE]: if...else Vs. The Conditional Operator (? :) ◼ We have studied the conditional operator (? : ) in the chapter “Operators and Expressions”. The working of conditional operator is exactly same as that of the if...else construct. i.e., Then what is the need of the if...else statements? ◼ The limitation of the conditional operator is that, after the ? or after the : only one C statement can be written. (expression1) ? (expression2) : (expression3); is same as if (expression1) { expression2; } else { expression3; } Dr. N. K. Pani, Dept. of CSEA, IGIT Sarang | 5.26

The switch Statement (Multi Way Decision) ◼ It is rather called the switch-case-break construct. ◼ Syntax: switch(expression) { case constant1: statement(s); break; case constant2: statement(s); break; ... ... default: statement(s); } Here, — expression corresponds to either an integer/character constant like 1, 2, 3, ‘a’, ‘b’, ‘c’ etc., or any C expression that is evaluable to an integer/character value. — constant1, constant2,... are integer/character constants like 1, 2, 3, ‘a’, ‘b’, ‘c’ etc. Each of these constants should be unique within a switch-case construct. — The break statements are optional. — The default level is optional. There can be at most one default level. — The default level may be placed any where but usually placed at the end. Dr. N. K. Pani, Dept. of CSEA, IGIT Sarang | 5.27

◼ Control Flow: ➢ The expression is evaluated 1st. ➢ Its value is then matched, one by one, in order, against constant1, constant2,...that follow the case levels. When a match is found, the program executes the set of statements corresponding to that case and all subsequent case and default as well (if a default is present). The control is then transferred to the statement immediately after the switch- case construct (i.e., after the closing curly brace of the switch-case construct). However, the break statement is meant for taking the control out of the current block (a block is a set of statements enclosed within a pair of curly braces). So, when a break statement is present within a case, it takes the control out of the switch-case construct on execution (i.e., transfers the control to the statement immediately after the switch-case construct). So, in this situation the set of statements corresponding to only that case is executed. Dr. N. K. Pani, Dept. of CSEA, IGIT Sarang | 5.28

➢ If no match is found with any of the case (that precedes the default), the program executes the set of statements corresponding to the default and all subsequent case (if at all present after the default ; recall that default can be placed any where). The control is then transferred to the statement immediately after the switch-case construct. Dr. N. K. Pani, Dept. of CSEA, IGIT Sarang | 5.29

◼ Examples: A few examples will clarify the control flow Sl. No. Example Output 1 void main() { int i = 2; switch(i) { case 1: printf("I am in case 1 n"); case 2: printf("I am in case 2 n"); case 3: printf("I am in case 3 n"); default: printf("I am in default n"); } } I am in case 2 I am in case 3 I am in default Dr. N. K. Pani, Dept. of CSEA, IGIT Sarang | 5.30

Sl. No. Example Output 2 void main() { int i = 2; switch(i) { case 1: printf("I am in case 1 n"); case 2: printf("I am in case 2 n"); case 3: printf("I am in case 3 n"); break; default: printf("I am in default n"); } } I am in case 2 I am in case 3 Dr. N. K. Pani, Dept. of CSEA, IGIT Sarang | 5.31

Sl. No. Example Output 3 void main() { int i = 2; switch(i) { case 1: printf("I am in case 1 n"); case 2: printf("I am in case 2 n"); break; case 3: printf("I am in case 3 n"); default: printf("I am in default n"); } } I am in case 2 Dr. N. K. Pani, Dept. of CSEA, IGIT Sarang | 5.32

Sl. No. Example Output 4 void main() { int i = 2; switch(i) { case 1: printf("I am in case 1 n"); break; case 2: printf("I am in case 2 n"); break; case 3: printf("I am in case 3 n"); break; default: printf("I am in default n"); } } I am in case 2 Dr. N. K. Pani, Dept. of CSEA, IGIT Sarang | 5.33

Sl. No. Example Output 5 void main() { int i = 10; switch(i) { case 1: printf("I am in case 1 n"); break; case 2: printf("I am in case 2 n"); break; case 3: printf("I am in case 3 n"); break; default: printf("I am in default n"); } } I am in default Dr. N. K. Pani, Dept. of CSEA, IGIT Sarang | 5.34

Sl. No. Example Output 6 void main() { int i = 10; switch(i) { case 1: printf("I am in case 1 n"); break; default: printf("I am in default n"); case 2: printf("I am in case 2 n"); break; case 3: printf("I am in case 3 n"); break; } } I am in default I am in case 2 Dr. N. K. Pani, Dept. of CSEA, IGIT Sarang | 5.35

Sl. No. Example Output 7 void main() { int i = 10; switch(i) { case 1: printf("I am in case 1 n"); break; default: printf("I am in default n"); break; case 2: printf("I am in case 2 n"); break; case 3: printf("I am in case 3 n"); break; } } I am in default Dr. N. K. Pani, Dept. of CSEA, IGIT Sarang | 5.36

Sl. No. Example Output 8 void main() { char ch = 'B'; switch(ch) { case 'a': case 'A': printf("'A' for apple n"); break; case 'b': case 'B': printf("'B' for ball n"); break; case 'c': case 'C': printf("'C' for cat n"); break; } } ‘B’ for ball Dr. N. K. Pani, Dept. of CSEA, IGIT Sarang | 5.37

◼ Programming Example 1: /* PR5_7.c: Program that reads an alphabet and prints whether it is a vowel or consonant*/ # include <stdio.h> # include <conio.h> void main() { char ch; printf("Enter an alphabet: "); scanf("%c", &ch); switch(ch) { case 'a': case 'A': case 'e': case 'E': case 'i': case 'I': case 'o': case 'O': case 'u': case 'U': printf("nIt is a vowel.n"); break; [Cont.] Dr. N. K. Pani, Dept. of CSEA, IGIT Sarang | 5.38

◼ Programming Example 2: For a student’s mark within 0-100, the index = (mark/25). The grades are calculated as follows: Index Grade 0 D 1 C 2 B 3 A Write a program that reads the mark within 0-100 and prints the appropriate grade. default: printf("nIt is a consonant.n"); } } Run 1: Enter an alphabet: p It is a consonant. Run 2: Enter an alphabet: u It is a vowel. Output Dr. N. K. Pani, Dept. of CSEA, IGIT Sarang | 5.39

/* PR5_8.c: Student’s Grade Calculation */ # include <stdio.h> # include <conio.h> void main() { int mark, index; printf("Enter mark (0-100): "); scanf("%d", &mark); index = mark/25; switch(index) { case 0: printf("nThe grade is: Dn"); break; case 1: printf("nThe grade is: Cn"); break; case 2: printf("nThe grade is: Bn"); break; case 3: printf("nThe grade is: An"); break; [Cont.] Dr. N. K. Pani, Dept. of CSEA, IGIT Sarang | 5.40

default: printf("nYou haven’t entered the mark within 0-100."); } } Run 1: Enter mark (0-100): 85 The grade is: A Run 2: Enter mark (0-100): 145 You haven’t entered the mark within 0-100. Output Dr. N. K. Pani, Dept. of CSEA, IGIT Sarang | 5.41

◼ Notes: 1. Though in all our programs we have put the case in some order, one can put the case in any order he likes. But the matching is always done in top to bottom order. void main() { int i = 10; switch(i) { case 78: printf("I am in case 78 n"); break; case 10: printf("I am in case 10 n"); break; case 196: printf("I am in case 196 n"); break; default: printf("I am in default n"); } } Dr. N. K. Pani, Dept. of CSEA, IGIT Sarang | 5.42

2. One can mix characters and integers in the cases (characters are actually integers). 3. Every statement in a switch-case must belong to some case. If a statement doesn’t belong to some case the compiler WON’T report an error, but the statement would never be executed. ... switch(i) { printf(“Enter a value: ”); /* This statement is never executed*/ case 100: j = i+50; printf(“%d n“, j); break; case 200: j = i-50; printf(“%d n“, j); break; } ... Dr. N. K. Pani, Dept. of CSEA, IGIT Sarang | 5.43

4. Though, the default level may be placed any where it should always be placed at the end. 5. In principle, a switch-case construct can be nested, but it is rarely practiced. 6. The switch-case construct is very helpful in writing menu driven programs. Switch-case Vs. The else-if Ladder ◼ Though both are meant for multi way decision making, there are some thing that simply can’t be done by using the switch-case: 1. switch-case are meant for equality comparisons. One can’t write a case that looks like: case i<=100. 2. A float value (any value other than integer/character) can’t be tested by using a switch. 3. A case can’t contain an expression like, a+3. 4. Multiple case can’t use the same expression. Dr. N. K. Pani, Dept. of CSEA, IGIT Sarang | 5.44

Assignments - I Complete the experiments given in “Lab Manual - Section 4”. Dr. N. K. Pani, Dept. of CSEA, IGIT Sarang | 5.45

Loop / Repetition / Iteration Control Structure

Introduction ◼ What is Looping?: Executing a set of statements repeatedly till a particular condition is true. ➢ A condition is nothing but an expression, evaluable to either true (non-zero) or false (zero). ➢ The condition tests a variable, known as the control variable that controls the number of times the loop is executed. ◼ The Overall Looping Process: The looping process, in general, involves the following four steps 1. Initialization: The control variable is assigned to some initial value. 2. Testing Using a Condition: The control variable is tested (using an expression). The result is either true (non-zero) or false (zero). 3. Executing the set of statements in the body of the loop. 4. Update: The control variable is updated (incremented, decremented, or any other operation that changes the value of the control variable). Dr. N. K. Pani, Dept. of CSEA, IGIT Sarang | 5.47

◼ Classification: Depending upon the position of the condition, a loop construct may be classified as 1. Entry controlled loop (pre-test loop) ▪ while loop ▪ for loop 2. Exit controlled loop (post-test loop) ▪ do-while loop Dr. N. K. Pani, Dept. of CSEA, IGIT Sarang | 5.48

The while Loop / Statement ◼ Syntax: ◼ Control Flow: The while is an entry-controlled loop. ➢ The condition is evaluated 1st. If it is true (non-zero), then the body of the loop is executed. After the execution of the body, the condition is once again evaluated and if it is true, the body is executed once again. This process is repeated until the condition finally becomes false (zero). ➢ When the condition becomes false, the loop is terminated, and the control goes to the statement immediately after the body of the loop. initialization; ... while(condition) { statement(s); update; } body of the loop Dr. N. K. Pani, Dept. of CSEA, IGIT Sarang | 5.49

◼ Programming Example 1: /* PR5_9.c: A program to calculate the sum of squares of numbers between 1 to 10. i.e., sum = 12+22+32+ ..... +102*/ # include <stdio.h> # include <conio.h> void main() { int sum = 0; int i = 1; /*Initialization*/ while(i<=10) /*Condition (Testing)*/ { sum = sum + (i*i); i++; /*Update (Incrementing)*/ } printf("The sum is: %dnn", sum); } The sum is: 385 Output Dr. N. K. Pani, Dept. of CSEA, IGIT Sarang | 5.50

◼ Programming Example 2: /* PR5_10.c: A program to evaluate the equation y = xn when n is a non-negative integer */ # include <stdio.h> # include <conio.h> void 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; /* Initialization */ while (count <= n) /*Condition (Testing)*/ { y = y*x; count++; /* Update (Incrementing) */ } printf("nx = %f; n = %d; nx to power n = %fn",x,n,y); } Enter the values of x and n: 12 5 x = 12.000000; n = 5; x to the power n = 248832.000000 Output Dr. N. K. Pani, Dept. of CSEA, IGIT Sarang | 5.51

◼ Notes: 1. If you forget to update the control variable (i.e., forget to write i++ or count++, as written in the last two programs within the body of the while loop), the loop becomes an infinite loop. 2. It is not necessary that the control variable must only be an int. It could also be a float (any numeric value). Again, the update doesn’t mean only incrementing or decrementing. It could be any operation, that eventually changes the control variable, so that the condition becomes false at some time. void main() { float a = 10.0; while(a <= 1000.0) { printf("Hin"); /* "Hi" is printed 6 times*/ a = a * 2.5; } } Dr. N. K. Pani, Dept. of CSEA, IGIT Sarang | 5.52

3. Never put a semicolon (;) immediately after the while clause. It will lead to an infinite loop. 4. What do you think would be the out put of the following program? int i; ... while(i <= 10); { printf(“%dn“, i); i++; } int i; ... while(i <= 10) ; { printf(“%dn“, i); i++; } is same as int i; ... while(i = 10) { printf(“%dn“, i); i++; } It is an infinite loop, because the condition (i = 10) is always true (non-zero). Dr. N. K. Pani, Dept. of CSEA, IGIT Sarang | 5.53

5. What do you think would be the out put of the following program? No, it doesn’t print numbers from 1 to 32767. It is an infinite loop. To begin with, it prints out numbers from 1 to 32767. After that, the value of i is incremented to 1, therefore it tries to become 32768, which falls outside the valid integer range (assuming that, the compiler gives 2 bytes for an int), so it goes to the other side and becomes -32768, which again satisfies the condition (i <= 32767). This process goes on indefinitely. void main() { int i = 1; while(i <= 32767) { printf(“%dn“, i); i++; } } Dr. N. K. Pani, Dept. of CSEA, IGIT Sarang | 5.54

The do-while Loop / Statement ◼ The Need (The difference between while and do-while): The while loop is an entry-controlled loop - meaning that - it executes the body of the loop only if the condition is true. However, on some occasions it might be necessary to execute the body of a loop at least once, even if the condition becomes false. In such situations, we should use an exit-controlled loop, like the do-while loop. ◼ Syntax: initialization; ... do { statement(s); update; } while(condition); body of the loop Notice the semicolon (;). It was not present in the syntax of the while loop. Dr. N. K. Pani, Dept. of CSEA, IGIT Sarang | 5.55

◼ Control Flow: As already mentioned the do-while is an exit-controlled loop. ➢ On reaching the do statement, the control proceeds to execute the body of the loop first. ➢ At the end of the loop, the condition in the while statement is evaluated. If it is true (non-zero), then the body of the loop is executed once again. This process is repeated till the condition finally becomes false (zero). ➢ Eventually, when the condition becomes false, the loop is terminated, and the control is transferred to the statement immediately after the while statement. Dr. N. K. Pani, Dept. of CSEA, IGIT Sarang | 5.56

◼ Programming Example: /* PR5_11.c: Program that continues to read a number and displays its square until the use says “NO”*/ # include <stdio.h> # include <conio.h> void main() { char status = ‘Y’; /*Initialization*/ int n; do { printf("nnEnter an integer: "); scanf("%d", &n); printf("nIts square is: %d", (n*n)); printf("nnWould you like to continue (Y/N)?: "); status = getche(); /*Update*/ }while(status == 'Y' || status == 'y'); /*Condition (Testing)*/ } Enter an integer: 5 Its square is: 25 Would you like to continue (Y/N)?: Y ... Output Dr. N. K. Pani, Dept. of CSEA, IGIT Sarang | 5.57

The for Loop / Statement ◼ The for loop is another entry-controlled loop that provides a more concise loop control structure. It allows initialization, testing using a condition, and update in a single line. ◼ Syntax: for(initialization; condition; update) { statement(s); } body of the loop Dr. N. K. Pani, Dept. of CSEA, IGIT Sarang | 5.58

◼ Control Flow: Demonstrated thorough the following diagram for(initialization; condition; update) { statement(s) } 1 2 3 4 if the condition is true if the condition is false Dr. N. K. Pani, Dept. of CSEA, IGIT Sarang | 5.59

◼ Programming Example 1: /* PR5_12.c The same program as that of PR5_9.c using the for loop (A program to calculate sum = 12+22+32+ ..... +102) */ # include <stdio.h> # include <conio.h> void main() { int sum = 0; int i; for(i=1; i<=10; i++) /*Initialization, Condition (Testing), and Update*/ { sum = sum + (i*i); } printf("The sum is: %dnn", sum); } The sum is: 385 Output Dr. N. K. Pani, Dept. of CSEA, IGIT Sarang | 5.60

◼ Programming Example 2: /* PR5_13.c A program to calculate the nth Fibonacci number */ /* Note: The Fibonacci series is : 0 1 1 2 3 5 8 ... */ # include <stdio.h> # include <conio.h> void main() { int n, i, fib1=0, fib2=1, fib; printf("nnEnter the value of n: "); scanf("%d", &n); for(i=1; i<=n-2; i++) { fib = fib1+fib2; fib1 = fib2; fib2 = fib; } printf("nThe %dth Fibonacci number is: %d", n, fib); getch(); } Enter the value of n: 7 The 7th Fibonacci number is: 8 Output Dr. N. K. Pani, Dept. of CSEA, IGIT Sarang | 5.61

◼ Notes: 1. In a for loop, both the initialization and the update sections can contain more than one expressions. If done so, the expressions should be separated by commas (,). For example: j=1; for(i=0; i<10; i++) { ... } Can be rewritten as /* More than one expressions initialized*/ for(i=0, j=1; i<10; i++) { ... } for(i=0; j<10; i++) { ... j++; } Can be rewritten as /* More than one expressions updated*/ for(i=0; j<10; i++, j++) { ... } j=1; for(i=0; j<10; i++) { ... j++; } Can be rewritten as /* More than one expressions initialized and updated*/ for(i=0, j=1; j<10; i++, j++) { ... } Dr. N. K. Pani, Dept. of CSEA, IGIT Sarang | 5.62

2. However, the condition section must contain exactly one expression (the expression may contain only the control variable, or other variables along with the control variable). 3. Writing the initialization, or the condition, or the update sections, within the for statement, is optional. However, the semicolons (;) separating the sections must remain. The following examples will clarify the concept ... i=5; /* Initialization is written here */ for( ; i<100 ; i=i+5) /* Contains the condition and the update*/ { printf(“%dn”, i); } ... Dr. N. K. Pani, Dept. of CSEA, IGIT Sarang | 5.63

... i=5; /* Initialization is written here */ for( ; i<100 ; ) /* Contains only the condition */ { printf(“%dn”, i); i = i+5; /* Update is written here */ } ... ... i=5; /* Initialization is written here */ for( ; ; ) /* Contains only the semicolons*/ { printf(“%dn”, i); if (i>100) /* Condition is written here */ break; i = i+5; /* Update is written here */ } ... Dr. N. K. Pani, Dept. of CSEA, IGIT Sarang | 5.64

4. If we completely remove the condition section, or the update section, or both form the for loop then it will be an infinite loop. The following examples will clarify the concept for(i=0; ; i++) /* No condition; Infinite loop*/ { printf(“%dn”, i); } for(i=0; i<10 ; ) /* No update; Infinite loop*/ { printf(“%dn”, i); } for(i=0; ; ) /* No condition and update; Infinite loop*/ { printf(“%dn”, i); } for(; ;) /* No condition and update; Infinite loop (the easiest way to write an { infinite loop)*/ printf(“%dn”, i); } Dr. N. K. Pani, Dept. of CSEA, IGIT Sarang | 5.65

Nesting of Loops ◼ The way if and switch statements can be nested, similarly the loops can also be nested by placing one within another. ◼ Programming Example 1: /* PR5_14.c A program to display all prime numbers from 1 to n */ # include <stdio.h> # include <conio.h> void main() { int i, j, n, num; printf("nEnter a range: "); scanf("%d", &n); printf("nThe prime numbers within the range 1-%d are: ", n); [Cont.] Dr. N. K. Pani, Dept. of CSEA, IGIT Sarang | 5.66

for(i=1;i<=n;i++) { num = i; for(j=2;j<num;j++) { if(num%j == 0) break; } if(num == j) { printf("%d ", num); } } getch(); } Enter a range: 20 The prime numbers within the range 1-20 are: 2 3 5 7 11 13 17 19 Output Dr. N. K. Pani, Dept. of CSEA, IGIT Sarang | 5.67

◼ Programming Example 2: Write a program to print the following structure 1 1 2 1 2 3 1 2 3 4 /* PR5_15.c A program to display right pyramid */ # include <stdio.h> # include <conio.h> void main() { int row, col; for(row=1;row<=4;row++) { for(col=1;col<=row;col++) { printf("%d ", col); } printf("nn"); } getch(); } Dr. N. K. Pani, Dept. of CSEA, IGIT Sarang | 5.68

◼ Programming Example 3: Write a program to print the following structure 1 1 2 1 1 2 3 2 1 1 2 3 4 3 2 1 /* PR5_16.c A program to display full pyramid */ # include <stdio.h> # include <conio.h> void main() { int row, col, space; for(row=1;row<=4;row++) { for(space=1;space<=4-row;space++) printf(" "); for(col=1;col<=row;col++) printf("%d ", col); for(col=col-2;col>=1;col--) printf("%d ", col); printf("nn"); } getch(); } Dr. N. K. Pani, Dept. of CSEA, IGIT Sarang | 5.69

Introduction ◼ The jump (unconditional jump) is implemented through the following statements. ➢ continue ➢ break ➢ return ➢ exit() ➢ goto ◼ exit()is a library function; rest are key words. Dr. N. K. Pani, Dept. of CSEA, IGIT Sarang | 5.71

The continue Statement ◼ The continue statement can only be used within a loop construct. ◼ Syntax: ◼ What It Does?: When executed (within a loop), it takes the control directly to the next iteration (i.e., to the condition clause) of the current loop, skipping all the statements after the continue statement within the loop. ➢ A continue is usually associated with an if. for(initialization; condition; update) { ... if(...) continue; ... } continue; Dr. N. K. Pani, Dept. of CSEA, IGIT Sarang | 5.72

◼ Programming Example: /* PR5_17.c A program to display the odd numbers between 1 to 10 */ # include <stdio.h> # include <conio.h> void main() { int i; printf("nThe odd numbers between 1-10 are: "); for(i=1;i<=10;i++) { if(i%2 == 0) { continue; } printf("%d ", i); } getch(); } The odd numbers between 1-10 are: 1 3 5 7 9 Output Dr. N. K. Pani, Dept. of CSEA, IGIT Sarang | 5.73

The break, return, and exit() Statements ◼ Unlike the continue statement which can be explicitly used within a loop, the break, return, and exit() statements can be used any where in a program (there is no restriction). break ◼ We have already used break statements before. ◼ Syntax: ◼ What it Does?: When executed, it takes the control out of the current block (recall that, a block is a set of statements enclosed within a pair of curly braces). break; while(...) { for(...) { ... break; ... } } Dr. N. K. Pani, Dept. of CSEA, IGIT Sarang | 5.74

return ◼ Syntax: The components in the square brackets are optional. ◼ What it Does?: The return statement terminates the execution of the current function and takes the control to the calling function immediately following the function call. A return statement can also return a value to the calling function. More on the return statement will be discussed in the chapter “Functions”. return [(][expression][)]; Dr. N. K. Pani, Dept. of CSEA, IGIT Sarang | 5.75

exit() ◼ Syntax: The component in the square brackets is optional. ◼ What it Does?: The exit() statement (function) takes the control out of the whole program (i.e., terminates the program). ➢ exit() optionally takes an integer constant as its argument. Normally, a zero as an argument (exit(0)) is used to indicate normal termination of the program (to the operating system) and a non-zero value as an argument is used to indicate termination of program due to some error or abnormal condition. ➢ An exit() is usually associated with an if. ◼ [NOTE]: The description of exit() is present in the header file “stdlib.h”. So, in order to use exit() we must include the header file “stdlib.h” in our program through the preprocessor directive #include<stdlib.h>, otherwise we may get a warning. exit([integer_constant]); Dr. N. K. Pani, Dept. of CSEA, IGIT Sarang | 5.76

◼ Programming Example: /* PR5_18.c A program that tests a number to be prime or not (A prime number is a natural number greater than 1 that has no positive divisors other than 1 and itself.) */ # include <stdio.h> # include <conio.h> # include <stdlib.h> void main() { int i, num; printf("nEnter an positive integer: "); scanf("%d", &num); for(i=2;i<=num-1;i++) { if(num%i == 0) { printf("n%d is a NOT a prime number.nn", num); exit(0); } } printf("n%d is a prime number.nn", num); } Enter a number: 56 56 is NOT a prime number. Output Dr. N. K. Pani, Dept. of CSEA, IGIT Sarang | 5.77

The goto Statement ◼ A word of caution: Avoid goto statement. It is not at all required for a highly structured language like C (we are discussing it for the shake of completeness). There are two reasons for it: 1. It obscures the normal control flow of the program (as we shall see, a goto statement can cause the control to jump anywhere in the program without any reason). Hence, the program becomes difficult to understand and debug. 2. Almost always, we can write the same program by using other control statements like if, switch, exit() etc., in an easy and more elegant manner. Dr. N. K. Pani, Dept. of CSEA, IGIT Sarang | 5.78

◼ Syntax: ◼ Control Flow: During the execution of a program, when a statement like “goto begin;” is met, the control will jump to the statement immediately following the label “begin:”. This happens unconditionally. [NOTE]: In a backward jump (when the “label:” is placed before the “goto label;” statement), the program will fall in an infinite loop if no condition is specified (though another goto or an if statement) to take the control after the “goto label;” statement. Few Explanations ▪ The goto requires a label in order to identify the place of jump. The label is nothing but an identifier name. ▪ The label must be followed by a colon. ... goto label: ... label: statement; ... (Forward Jump) ... label: statement; ... goto label: ... (Backward Jump) Dr. N. K. Pani, Dept. of CSEA, IGIT Sarang | 5.79

◼ Programming Example 1 (This is the 1st and last time we are doing a program using goto): /* PR5_19.c A program that illustrate the use of goto */ # include <stdio.h> # include <conio.h> void main() { int i, j, k; for(i=1;i<=2;i++) { for(j=1;j<=2;j++) { for(k=1;k<=2;k++) { if(i==2 && j==2 && k==2) goto end; else printf("%d %d %dn", i, j, k); } } } end: printf("nOut of the loop at last !!nn"); } 111 112 121 122 211 212 221 Out of the loop at last !! Output Dr. N. K. Pani, Dept. of CSEA, IGIT Sarang | 5.80

◼ Programming Example 2 (Rewriting the previous program without using goto): /* PR5_20.c: Program to print the series as in PR5_19.c without using goto. */ # include <stdio.h> # include <stdlib.h> void main() { int i, j, k; for(i=1;i<=2;i++) { for(j=1;j<=2;j++) { for(k=1;k<=2;k++) { if(i==2 && j==2 && k==2) { printf("nOut of the loop at last!!nn"); exit(0); } else printf("%d %d %dn", i, j, k); } } } } 111 112 121 122 211 212 221 Out of the loop at last !! Output Dr. N. K. Pani, Dept. of CSEA, IGIT Sarang | 5.81

Assignments - II Complete the experiments given in “Lab Manual - Section 5”. Dr. N. K. Pani, Dept. of CSEA, IGIT Sarang | 5.82

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