How Create a C++ Program

#include<iostream>using namespace std; void main() { cout<<“Hello World”;}

If your compiler gives error then

#include<iostream.h>void main() { cout<<“Hello World”; cout<<endl; // for going to new line cout<<“ good bye”;}

cout is an object for printing out some thing on the screen.

#include<iostream.h>void main() { cout<<“Hello World \n”; cout<<“ good bye”;}

we can use \n instead of cout<<endl;

How to run your program

• Using Linux or unix:g++ myFile.cpp

./a.out

g++ myFile.cpp myFile.out

./myFile.out

Declare Statement & Variable• Each variable must be declare before use• Each variable has a type:

For example int , char, float. int for Integer type; char for character like ‘A’; float for real number;

Example

int LuckyNumber=17;

float RealNumber;

char a=‘A’;

Identifiers

• Identifier: name of a variable, function, or class • Rules for identifiers in C++:

1 Can be made up of letters, digits, and the underscore (_) character

2 Cannot start with a digit 3 Cannot use other symbols such as ? or % 4 Spaces are not permitted inside identifiers 5 You cannot use reserved words 6 They are case sensitive

Self Check

1. What is the type of the values 0 and ‘0’?

2. Which of the following are legal identifiers?

Greeting1gvoid101dalmatiansHello, World<greeting>

Answer

• int and char

• Only the first two are legal identifiers

Syntax : Variable Definition

• typeName variableName = value;or typeName variableName;

Example :int number = 12;

Purpose:To define a new variable of a particular type and optionally

supply an initial value

The Assignment Operator

• Assignment operator: =

• Not used as a statement about equality

• Used to change the value of a variable

int number1; int number2, number3;

number1=number2=number3=88;

number2=number2-1;

number3=number2+1;

How to read a variable

#include<iostream>using namespace std; void main() { int number; cout<<“please enter a number \n”; cin>>number; number=number+1; cout<<“the number is “<<number;}

Integer Types

• The short, int and long Integer Types

A short integer is at least 16 bits

An int integer is at least as big as short

A long integer is at least 32 bits and at

least as big as int .

• E.g. A 16-bit int might run from -32768 to 32767

• The sizeof operator returns the size (in bytes)

#include<iostream.h>int main() { int n_int = INT_MAX; short n_short = SHRT_MAX; long n_long = LONG_MAX; cout << “int is “ << sizeof (int) << “ bytes” << endl; cout << “short: “ << n_short << endl; cout << “long: “ << n_long << endl; return 0;}

• int is 4 bytes

• Maximum values:– Short: 32767

– Long: 2147483647

Characters and small integers#include<iostream.h>int main() { char ch = ‘M’; // assign ASCII code int a = ch; cout << “ASCII code: “ << ch << “ is “ << a << endl; ch = ch + 1; a = ch; cout << “ASCII code: “ << ch << “ is “ << a << endl;

return 0;}

Output

• M is 77

• N is 78

Boolean type

• bool isReady = true;

• int ans = true; // ans assigned 1

• int promise = false; // promise assigned 0

• bool start = -100; // true

• bool stop = 0; // false

Floating-point number

• E.g. • 12.34• 9300.3• 0.02• 8.0

• We have

float, double, long double

Arithmetic operators

• Summation: +

• Multiplication: *

• Division: /

• Subtraction: -

Operator Precedence

• int number = 3 + 4 * 5 // 35 or 23?

• float logs = 120 / 4 * 5 // 150 or 6??

Type Casting

• Conversion between types:• (typeName) value // c• typeName (value) // c++• e.g.

– cout << int(‘A’) << endl; // 65– float one, – int two;

• one = 1.9 + 2.1;• two = (int) 1.9 + (int) 2.1;