Macros :

Macros are symbolic constants and they are used for improving the readability.

The general syntax for defining the macro is ,

#define macroname macroexpansion

e.g.#define MAX 50

Now,     MAX  is a macro and where ever we write MAX  it will be considered equivalent to 50.

And also ,

MAX=60;

will results in an error, as MAX  is replaced by 50 , so the statement means ,

50=60;

as we cannot assign one constant into another so it will give an error .

Consider the following code ,

       #include<iostream.h>

       #include<conio.h>

       #define PI 3.14

       void main()

       {

              float radius,area,circum;

              clrscr();

              cout<<endl<<"Enter the radius of the circle :";

              cin>>radius;

              //calculate the area of the circle

              area=PI * radius * radius;

              // calculate the circumference of the circle

              circum  = 2 * PI  * radius ;

              cout<<endl<<"Area of circle :" << area;

              cout<<endl<<"Circumference of the circle :"<<circum;

              getch();

}