贺老师教学链接  C语言及程序设计进阶 本课讲解

宏定义

#include <stdio.h>
#define PI 3.1415926 
int main ( )
{
  float r,l,s,sq,vq;
  printf("please enter r:");
  scanf("%f", &r);
  l=2 * PI *r;	
  s=r * r * PI;	
  sq=4* PI * r * r;
  ……
} 

带参数的宏定义

#include <stdio.h>
#define S(a,b) a*b
int main()
{
    printf("矩形1面积: %d\n", S(2, 4));
    printf("矩形2面积: %.2f\n", S(2.3, 4.5));
    return 0;
}

谨慎带参数的宏定义的副作用

#include <stdio.h>
#define PI 3.1415926
#define S(r) PI*r*r
int main( )
{
    float a, area, b;
    a=1;
    b=2;
    area=S(a+b);
    printf("r=%.2f, area=%.2f\n", a+b, area);
    return 0;
}