include <stdio.h>

int main()
{

double num1, num2; 
char op;
printf("请输入算式：  

");

scanf("%lf %c %lf", &num1, &op, &num2);  

switch(op) { 

    case '+': 
        printf("%.2lf + %.2lf = %.2lf",num1, num2, num1 + num2); 
        break;  

    case '-': 
        printf("%.2lf - %.2lf = %.2lf",num1, num2, num1 - num