c語言type錯誤怎么解決？

#include <stdio.h>

int main ()

{

double power (double x,double y);

double result;

double x=2.0,y=3.0;

result = power (x , y);

printf("%f的%f次方等于%f",x,y,result);while(1);

return 0;

}

double power (double x,double y)

{

double z=1,i;

for(i=1;i<=y;i++)

{

z=z*x;

}

return z;

}