第三章3-9

#include<stdio.h>
int main(void)
{
 double value1,value2;
 char op;

 printf("Type in an expression:");
 scanf("%lf%c%lf",&value1,&op,&value2);
 switch(op){
     case'+':
   printf("=%.2f\n",value1+value2);
   break;
  case'-':
   printf("=%.2f\n",value1-value2);
   break;
  case'*':
   printf("=%.2f\n",value1*value2);
   break;
  case'/':
   printf("=%.2f\n",value1/value2);
   break;
  default:
   printf("Unknown operator\n");
   break;
 }

 return 0;
}