Constants and the C Preprocessor

 1 #include <stdio.h>
 2 #define    PI 3.14159
 3 int main(void){
 4     float area, circum, radius;
 5
 6     printf("What is the radius of your pizza>\n");
 7     scanf("%f", &radius);
 8     area = PI * radius *

 radius;
 9     circum = 2 * PI *radius;
10     printf("Your pizza parameters are as follows:\n");
11     printf("Circumference = %1.2f, area = %1.2f \n", circum, area);
12     getchar();
13     return 0;
14 }

The #define statement can be used for character and string constants,too . The following example are valid:

1 #define BEEP ‘\a‘
2 #define TEE ‘T‘
3 #define ESC ‘\033‘
4 #define OOPS "Now you have done it!"

Remember:1 It is a sensible C tradition to type constants in uppercase.2 Don‘t make the common error when using the #define.3 The const Modifier makes variables read-only ;you cannot alter the value of the variables.4 C has a third way to create symbolic constants,and that is the enum.