#include<stdio.h>
main()
{
  loop: float a,b,sum;
  char c,x;
  scanf("%f%c%f",&a,&c,&b);
  getchar();
    {
    if(c=='+')
    printf("sum=%f",sum=a+b);
    else if (c=='-')
      printf("sum=%f",sum=a-b);
      else if(c=='*')
        printf("sum=%f",sum=a*b);
        else if(b!=0&&c=='/')
             printf("sum=%f",sum=a/b);
     }
     printf("\n");
     printf("Do you want to continue?y/n");
     if(x=getchar()=='y')
       goto loop;
     else EOF;
 }

printf ("num1 " #op " num2" " = %lf ", res)#op是什么意思,为什么op前要加#,大哥请帮忙解说一下