c语言的switch错误，帮我看看吧

#include…
…
case'+':printf("%lf+%lf=%lf",a,b, (a + b)); break;
case'-':printf("%lf-%lf=%lf",a,b,(a-b)); break;
case'':printf("%lf%lf=%lf",a,b, (a * b)); break;
case'/':printf("%lf/%lf=%lf",a,b, (a / b)); break;
}
}

请详细描述一下

感觉你这switch没问题啊
反而是你那个输入