第三章3-11

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

 printf("Type in an expression:");
 scanf("%lf%c%lf",&value1,&op,&value2);
 if(op=='+')
  printf("=%.2f\n",value1+value2);
 else if(op=='-')
  printf("=%.2f\n",value1-value2);
 else if(op=='*')
  printf("=%.2f\n",value1*value2);
 else if(op=='/')
  if(value2!=0)
      printf("=%.2f\n",value1/value2);
  else
   printf("Divisor can not be 0!\n");
 else
  printf("Unknown operator!\n");
 return 0;
}