Key Concepts of C++ computer language.ppt

Tokens  The smallest individual units in a program are known as tokens.  Keywords  Identifiers  Constants  Operators  Strings

Keywords  They are explicitly reserved identifiers and cannot be used as names for the program variables or other user-defined program elements.

keyword asm else operator throw auto enum private true bool explicit protected try break extern public typedef case false register typeid catch float reinterpret_cast typename char for return union class friend short unsigned const goto signed using const_cast if sizeof virtual continue inline static void default int static_cast volatile delete long struct wchar_t do mutable switch while double namespace template dynamic_cast new this

Identifiers  An identifiers is made of one or more characters  The first character must be a letter or an underscore. All following characters can be letters, numbers or underscores  No limit on the length of a variable’s name.  Names starting with an underscore or with a double underscore are normally reserved to system use!  C++ is case sensitive! const int Entries; double _attempts; double 2A; // error!

Predefined types in C++  All numeric types to represent integer numbers, real numbers and character variables are predefined

Name Description Size* Range* char Character or small integer. 1byte signed: -128 to 127 unsigned: 0 to 255 short int (short) Short Integer. 2bytes signed: -32768 to 32767 unsigned: 0 to 65535 int Integer. 4bytes signed: -2147483648 to 2147483647 unsigned: 0 to 4294967295 long int (long) Long integer. 4bytes signed: -2147483648 to 2147483647 unsigned: 0 to 4294967295 bool Boolean value. It can take one of two values: true or false. 1byte true or false float Floating point number. 4bytes +/- 3.4e +/- 38 (~7 digits) double Double precision floating point number. 8bytes +/- 1.7e +/- 308 (~15 digits) long double Long double precision floating point number. 8bytes +/- 1.7e +/- 308 (~15 digits)

Predefined types in C++ 123 O123 0x123 constant integers, decimal, octal, hexadecimal 123l 123u integers, long, unsigned ‘A’ ‘1’ ‘t’ character, tab 3.14f 3.1415 3.1415L float, double, long double 300e-2 .03e2 30e-1 double, scientific notation “Name” constant string true false boolean Literal constant ‘a’ alert ‘’ backslash ‘b’ backspace ‘r’ carriage return ‘”’ double quote ‘f’ form feed ‘t’ tab ‘n’ newline ‘0’ null character ‘’’ single quote ‘v’ vertical tab ‘101’ 101 octal, ‘A’ ‘x041’ hexadecimal, ‘A’ Constant character “” null string (‘0’) “name” ‘n’ ‘a’ ‘m’ ‘e’ ‘0’ “a ”string”” prints: a “string” “a string a at the end of the line spanning two lines” to continue on the next line String constant

Declaration of Variables  A declaration associates a meaning to an identifier  In C++ all entities must be declared before they can be used  A declaration is (often) a definition as well. For simple variables this means assigning a value to the variable, when the latter is declared const int i=100; // the i variable double max(double r1,double r2); // the max function const double pi=3.1415926; // definition double max(double r1, double r2) { // declaration return (r1>r2) ? r1: r2; // definition of max }

Scope  Variables can be declared and defined (almost) everywhere in a C++ program  A variable’s visibility (scope) depends on where a variable has been declared int func() { … const int n=50; // function scope for (int i=0;i<100;i++) // local i { double r; // local r ... } cout<<“n “<< n <<endl; // OK cout<<“i “<< i <<endl; // error! cout<<“r “<< r <<endl; // error! No doubt … }

Scope (2)  Beware! The same variable can be re-declared several time (with different scope). Don’t do that (if possible), this makes your program hard to follow and error prone! int i; // file (global) scope int func() { int i=50; // function scope, hides // i at file scope for (int i=0;i<100;i++) // block scope. Hides // i at function scope { int i; // this is an error... ... } cout<<“i “<< i <<“ “<< ::i <<endl; ... } Scope resolution operator

Symbolic Constants  The keyword const is used for declaring a constant variable  In C, people used the preprocessor to declare the constants  in this case, N is a constant with no type, the preprocessor will just substitute N with its value everywhere throughout the program, without respecting the strong typing rules (avoid)  a const variable must be initialized on creation const int N=100; N cannot be modified double w[N]; N is used here to declare a vector const int vect[5]= vect’s components cannot be {10,20,30,40,50}; modified Example for const #define N 100

Enumerated Data Types  Enum is the simplest form of user defined type in C++ enum Color { red, green, blue }; Color screenColor = blue; Color windorColor = red; int n = blue; // OK Color c = 1; // error! enum Cards { Hearts, Spades, Diamonds, Clubs };

Operators Arithmetic operators ( +, -, *, /, % ) The five arithmetical operations supported by the C++ language are: + addition - subtraction * multiplication / division % modulo

Operators Compound assignment (+=, -=, *=, /=, %=, >>=, <<=, &=, ^=, |=) expression is equivalent to value += increase; value = value + increase; a -= 5; a = a - 5; a /= b; a = a / b; price *= units + 1; price = price * (units + 1);

Operators Increase and decrease (++, --) Example 1 Example 2 B=3; A=++B; // A contains 4, B contains 4 B=3; A=B++ // A contains 3, B contains 4

Operators Relational and equality operators ( ==, !=, >, <, >=, <= ) == Equal to != Not equal to > Greater than < Less than >= Greater than or equal to <= Less than or equal to

Operators Logical operators ( !, &&, || ) && OPERATOR a b a && b true true true true fals e false fals e true false || OPERATOR a b a || b true true true true fals e true fals e true true

Operators Conditional operator ( ? ) condition ? result1 : result2 7==5 ? 4 : 3 // returns 3, since 7 is not equal to 5. 7==5+2 ? 4 : 3 // returns 4, since 7 is equal to 5+2. 5>3 ? a : b // returns the value of a, since 5 is greater than 3. a>b ? a : b // returns whichever is greater, a or b.

Operators Bitwise Operators ( &, |, ^, ~, <<, >> ) operator description & Bitwise AND | Bitwise Inclusive OR ^ Bitwise Exclusive OR ~ Unary complement (bit inversion) << Shift Left >> Shift Right

Operators Explicit type casting operator Type casting operators allow you to convert a data of a given type to another. There are several ways to do this in C++. The simplest one, which has been inherited from the C language, is to precede the expression to be converted by the new type enclosed between parentheses (()): int i; float f = 3.14; i = (int) f;

Operators sizeof() This operator accepts one parameter, which can be either a type or a variable itself and returns the size in bytes of that type or object: a = sizeof (char);

Statements empty ; expression j=j+k; composite { . . . . } used in functions,if.. Costitutes a block goto goto label; don’t use it! if if (p==0) cerr<<“error”; single branch if-else if (x==y) cout<<“the same”; else cout<<“different”; two branches for for (j=0;j<n;j++) declarations allowed a[j]=0; while while (i != j) 0 or more iterations i++; do-while do y=y-1; 1 or more iterations while (y>0); break break; leaves the block continue continue; next iteration Statement C++ comments

Statements switch switch (s) { case 1: use break not to fall ++i; in te following case case 2: add a default case at --i; the end of the case default: list ++j; }; declaration int i=7; in a block, file or namespace return return x*x*x; return value of a function Statement C++ comments

Composite statements  A composite statement is made of a series of statements between {}  Normally used for grouping statements is a block (if, for, while, do-while, etc.)  A function body is always made of a composite statement  A variable declaration can be put anywhere in a block. In this case, the variable scope will be the block itself

strings  The C++ language library provides support for strings through the standard string class. This is not a fundamental type, but it behaves in a similar way as fundamental types do in its most basic usage  A first difference with fundamental data types is that in order to declare and use objects (variables) of this type we need to include an additional header file in our source code: <string> and have access to the std namespace

strings // my first string #include <iostream> #include <string> using namespace std; int main (){ string mystring = "This is a string"; cout << mystring; return 0; }

Key Concepts of C++ computer language.ppt

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