C语言编程Time Limit Exceeded问题

为什么我的代码会Time Limit Exceeded

#include<stdio.h>
int main(){
int a,b;
char c;
float d;
int e;
while(scanf("%d%c%d",&a,&c,&b)!=EOF){
switch( c ){
case ’ + ':
{
e=a+b;
printf("%d\n",e);
break;
}
case ’ - ':
{
e=a-b;
printf("%d\n",e);
break;
}
case ’ * ':
{
e=a * b;
printf("%d\n",e);
break;
}
case ’ / ':
{
d=(float)a/b;
printf("%.2f\n",d);
break;
}
default: break;
}
}
return 0;
}