#include
#define PI 3.1415926
double circle(double r)//参数是半径
{
return (PI*r*r);//返回值是面积
}
int main()
{
double r,s;//半径,面积
printf("input r");
scanf("%lf",&r);
s=circle(r);
printf("%lf",s);
return 0;
}
double yuanmianji(double r)
{
return (r*r*3.14159);
}
#include
#include
#define PI 3.14
double area(int r){
return PI*pow(r,2);
}
void main(){
double r;
double Area;
scanf("%lf",&r);
Area=area(r);
printf("%lf\n",Area);
}