#include <iostream>
#include <string>

using namespace std;

int main() {
 fail:
  int x = 0,y = 0;
  char o;
  cout <<"Enter two numbers => ";
  cin >>x>>o>>y;
  while(true)
    {
      if(cin.fail())
	{
	  cout <<"Error : you are entered a character value ! ..."<<"\n";
	  cin.clear();
	  string il;
	  getline(cin, il);
	  goto fail;
	}
      else if(o=='+')
	{
	  cout <<"result = "<<x+y<<"\n";
	  break;
	}
      else if(o=='-')
	{
	  cout <<"result = "<<x-y<<"\n";
	  break;
	}
      else if(o=='*')
	{
	  cout <<"result = "<<x*y<<"\n";
	  break;
	}
      else if(o=='/')
	{
	  cout <<"result = "<<x/y<<"\n";
	  break;
	}
      else if(o=='%')
	{
	  cout <<"result = "<<x%y<<"\n";
	  break;
	}
      else
	{
	  cout <<"invalid operation ! ..."<<"\n";
	  break;
	}
    }
  return 0;
}