Thread: sentinel controlled do-while loop

In my code I need to have a sentinel controlled do-while loop for the number 0. I can get it to work when I use a while loop, but cant get it to work when I use a do-while.

Code:

#include <iostream>
using namespace std;

int main()
{
  int number, x;
  cout << "Enter an integer: ";
  cin >> number;

  x = 1;
  
  do
  {
    
    if (number % 2 == 0)
    cout << number << " is evener." << endl;

    if (number % 2 != 0)
    cout << number << " is odder." << endl;
    x++;
   
    cout << "Enter an integer: ";
    cin >> number;
    
    }while(number != 0);

  
  return 0;
}

For some reason it wont work if I enter 0 for the first input, but anytime after the first input it will terminate the program. What am I doing wrong that it will terminate when I enter 0 anytime after the first input?

Using while does the check at the beginning of the loop, whereas do-while does the check at the end of the loop. A do-while loop always executes at least once.

Originally Posted by kmdv

If the exercise says "even if 0 is entered the first time [show it is an even number instead of exiting]" it is correct.

It says even if the number is 0 for the first entry, it should still exit.

Originally Posted by iMalc

Don't ask for an integer from two different places. You've got code duplication. You only need that one one place, just inside the top of the loop.

Ok thanks. That almost fixes it. It prints out that 0 in even and then ends the program. How do I make it so that it just ends it without printing that 0 is even first?

Originally Posted by kmdv

Code:

cout << "Enter an integer: ";
cin >> number;
while(number != 0)
{
  if (number % 2 == 0)
    cout << number << " is even." << endl;
  else
    cout << number << " is odd." << endl;
  cout << "Enter an integer: ";
  cin >> number;
}

I know how to do it using a while loop, but I must use a do-while loop.

In that case you'd need to add an extra number==0 check at the start of the loop and break if true. Not exactly the cleanest way of doing it but then again neither is using do-while where while is more appropriate.