#include "stdio.h"
 #include "math.h"
double pin (float x, int N)
{   double y;
    if(N==0) return 0;
    else y=sqrt(x+pin(x,N-1));
    return y;
 }
main()
{   float x,y;
    int N;
    printf("please input x and N:");
    scanf("%f%d",&x,&N);
    y=pin(x,N);
    printf("y=%f\n",y);
 }

可以运行啊....... 没有问题

可以运行，就是有个警告

#include "stdio.h"
#include "math.h" 
double pin (double x, int N) //都用double型吧
{   double y; 
    if(N==0) return 0; 
    else y=sqrt(x+pin(x,N-1));
    return y;
} 
main() 
{   double x,y;//都用double型吧
    int N; 
    printf("please input x and N:"); 
    scanf("%lf%d",&x,&N); //都用double型吧
    y=pin(x,N); 
    printf("y=%lf\n",y); //都用double型吧
}

新手，弱弱的问一句，结果是不是都是根号下X？

这个是对一个数进行N的求解算术平方根吧