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.
Constants and the C Preprocessor
原文：http://www.cnblogs.com/michael2016/p/6580050.html