Question

consider this code snippet

   void make(int n)
   {
     std::string user_input;
     std::istringstream iss(user_input);
     char letter;
     int index;
     while(n>0)
    { cout<<n<<endl;
      std::getline(std::cin, user_input);
      while (iss >> letter >> index)
      cout<<letter<<' '<<index;
      n--;
    }
   }  
   int main()
   { int n;
     cin>>n;
     make(n);
     return 0; 
   }

here loop is not running correctly
if i put n=5 then output is

5
//getline doesn’t work
4
then getline works… why this

Answer 1

The reason why it’s doing this, is because when you’re calling getline(), it’s taking what’s in cin and putting it in the variable. However, when you initially called cin to take in the inital input, the newline character remained in the buffer after going into your make() function.

So when you enter the loop, the first getline() takes '\n' from cin, and the buffer was cleared. That’s why it seems to “skip” the first iteration as it would seem.

So in order to get it to function correctly, you should clear your input buffer when you call your function using cin.ignore(), like so:

 void make(int n)
 {
 cin.ignore(1000,'\n'); //ignores 1000 characters or until sees \n
 std::string user_input;
 std::istringstream iss(user_input);
 char letter;
 int index;
 while(n>0)
{ cout<<n<<endl;
  std::getline(std::cin, user_input);
  while (iss >> letter >> index)
  cout<<letter<<' '<<index;
  n--;
}
}  
int main()
{ int n;
  cin>>n;
  make(n);
  return 0; 
 }

I haven’t used c++ much recently, so at the moment, i’m not sure if there’s a better way to handle this, but this should give you a good direction.