为什么如下这个c语言函数输出没有值？

Question

#include <stdio.h>
double fnFun(double x);
double fnFun(double x)
{
double i;
if(x>1)
i=x*x+1;
else if(x<=1&&x>=-1)
i=x*x;
else
i=x*x-1;
return (i);
}
void main()
{
double x;
printf("请输入x的值\n");
scanf("%f",&x);
printf("%.2f\n",fnFun(x);
}

Answer 1

#include <stdio.h>double fnFun(double x);double fnFun(double x){double i;if(x>1)i=x*x+1;else if(x<=1&&x>=-1)i=x*x;elsei=x*x-1;return (i);}void main(){double x;printf("请输入x的值\n");scanf("%lf",&x);printf("%.2lf\n",fnFun(x));}没有弄清float和double,我这个可以的