实验一

#include<stdio.h>
int main(void)
{
    double R,S;
    printf("Enter R:\n");
    scanf("%lf",&R);
    if(R<=0){
    printf("Enter is wrong !");
    }
    else{
        S=3*R*R;
    }
        printf("S=%lf\n",S);

    return 0;
}