The #define Directive

The #define directive explains a macro which is a text string represented by a name. Whenever the pre-processor finds this name in the program, it is replaced by the text string it shows. The is an following example which explains a value and gives it a name PI.

                #define PI 3.14285    // no semicolon given

                void main()

                 {

                                cout << PI;

                 }

This program is equivalent to :

                void main()

                 {

                                cout << 3.14285;

                 }

The  # define directive works strictly on the basis of substitution of a text string for the macro names.