已經測試，執行正常，先輸入兩個數，然後輸入+-*/中的一個：接著就有結果

#include <stdio.h>

#include <stdlib.h>

int main(void)

{

float a, b;

char c;

float res;

scanf("%f %f\n", &a, &b);

c = getchar();

switch (c)

{

case "+":

res = a + b;

break;

case "-":

res = a - b;

break;

case "*":

res = a * b;

break;

case "/":

res = a / b;

break;

default:

printf("input error\n");

}

printf("result is: %f\n", res);

return 0;

}