10-14

#include<stdio.h>
int main(void)
{
    double R,S;
    printf("Enter R:");
    scanf("%lf",&R);
    if(R<=0){
        printf("Enter wrong!");
    }
    else{
        S=3.14*R*R;
    }
   
    printf("S=%lf\n",S);
    return 0;
}