#include<stdio.h>    //#include<stdio.h>
#define P 3.1415926  //#define P 3.1415926
main(){              //main(){
double r,s;          //float r,s;
printf("\n输入半径:");//printf("\n输入半径:");
scanf("%lf",&r);      //scanf("%f"&r);
s=P*r*r;              //s=P*r*r;
printf("圆面积%lf",s);//printf("圆面积%f",s);
return(main());       //return(main());
}                     //}