四则运算

#include <stdio.h>  

void fun(char,double,double); 

void main() 

{ 
char signal; 
double x; 
double y; 
while (1)
{ 
printf("please input first number : "); 
scanf("%lf",&x);  
loop:printf("please input operater : "); 
scanf("%s",&signal); 
if (signal!='+'&&signal!='-'&&signal!='*'&&signal!='/') 
{ 
printf("operater illegal ! \n"); 
goto loop; 
} 
printf("please input second number : "); 
scanf("%lf",&y); 
fun(signal,x,y); 
printf("\n"); 
} 
}  
void fun(char signal,double x,double y) 
{ 
if (signal=='*') 
{  
printf("%lf*%lf=%lf",x,y,x*y); 
} 
else if (signal=='/')
{ 
if (y==0) 
{ 
printf("除数不能为零"); 
} 
else 
{  
printf("%lf/%lf=%lf",x,y,x/y);