#include <stdio.h>
#include <stdlib.h>
#define R 1
#define PI 3.1415
int main() {
float r, s1, s2;
printf("请输入一个数: \n");
scanf("%f", &r);
#if R
s1 = PI * r * r;
printf("圆的的面积为: %f\n", s1);
#else
s2 = r * r;
printf("正方形面积为 %f\n", s2);
#endif
system("pause");
return 0;
}