Basic I/O, Variables and Constants

1. Hello World:

    Code Listing: 

(Note: lines started with // are comments, which will be ignored by the compiler)

// Purpose: A simple C++ program which prints "Hello World!" on the screen

#include // need this header file to support the C++ I/O system
using namespace std; // telling the compiler to use namespace "std",
// where the entire C++ library is declared.

int main()
{
// Print out a sentence on the screen.
// "<<" causes the expression on its right to
// be directed to the device on its left.
// "cout" is the standard output device -- the screen.
cout << "Hello World!" << endl;
return 0; // returns 0,which indicate the successful
// termination of the "main" function

}

    Running session:

Hello World!

2. Variables and Constants

Code listing:

// Purpose: Demonstrate the use of variables and constants
//
#include
using namespace std;
// declaring a constant. It's value cannot be changed.
const int CONST_VAL = 5;
int main()
{
int iValue; // An integer variable
float fValue; // A floating point variable
char cValue; // A character variable

iValue = 1234; // Assigns 1234 to iValue
fValue = 1234.56; // Assigns 1234.56 to fValue
cValue = 'A'; // Assigns A to cValue

// Now print them out on the screen:
cout << "Integer value is: " << iValue << endl;
cout << "Float value is: " << fValue << endl;
cout << "Character value is: " << cValue << endl;
cout << "The constant is: " << CONST_VAL << endl;

return 0;
}

Running session:

Integer value is: 1234
Float value is: 1234.56
Character value is: A
The constant is: 5
 

3. Basic IO

Code listing:

// Purpose: Converts gallons to liters

#include
using namespace std;

int main()
{
float gallons, liters;

cout << "Enter number of gallons: ";
cin >> gallons; // Read the inputs from the user

liters = gallons * 3.7854; // convert to liters

cout << "Liters: " << liters << endl;

return 0;
}

Running session:

Enter number of gallons: 14
Liters: 52.9956