Non-terminating while loop

Question

I was just wondering something. I have the following code:

#include <iostream>
using namespace std;

int main()
{
    int number, largest, counter = 1;
    while (counter <= 10)
    {
          cout << "Enter a number: ";
          cin >> number;
          if (counter = 1)
          {
               largest = number;
          }
          else if (number > largest)
          {
               largest = number;
              }
          counter++;
    }
    cout << "\n\nThe largest number is: " << largest;
    system("pause");
    return 0;
}

The thing is, it never terminates. I did manage to fix the problem by modifying the code a little, but I was wondering why this happened. Here is the fixed code:

#include <iostream>
using namespace std;

int main()
{
    int number, largest, counter = 1;
    cout << "Enter a number: ";
    cin >> number;
    largest = number;
    while (counter < 10)
    {
      cout << "Enter a number: ";
      cin >> number;
      if (number > largest)
      {
           largest = number;
      }
      counter++;
    }
    cout << "\n\nThe largest number is: " << largest << endl;
    system("pause");
    return 0;
}

It seems that after removing the else if statement it worked. What happened?

If I'd be the compiler I'd say like "Cannot implicitly convert type int to bool" or like "you shouldn't set a variable in if" or like "hey Emile wazzup why use only one = in if?Try ==." — Bastardo
– Bastardo, Commented Jun 30, 2011 at 13:43
@JohnnyCageWins. My compiler (MSVC) says something along the lines... — Armen Tsirunyan
– Armen Tsirunyan, Commented Jun 30, 2011 at 13:44

MGZero · Accepted Answer · 2011-06-30 13:36:48Z

8

if (counter = 1)

this should be

if (counter == 1)

otherwise, you're going to reset your counter to 1 each iteration.

answered Jun 30, 2011 at 13:36

MGZero

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Comments

RedX · Accepted Answer · 2011-06-30 13:36:32Z

4

if (counter = 1) reassigns 1 to counter every loop this being always < 10.

You want if (counter == 1).

answered Jun 30, 2011 at 13:36

RedX

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Comments

Grigor Gevorgyan · Accepted Answer · 2011-06-30 13:46:46Z

4

A common mistake:

if( counter = 1) // assignment operator

This will set counter's value to 1 at each iteration, and the loop never finishes.

You should use

if( counter == 1) // equality operator
           ^^^^

which is exactly what you mean

edited Jun 30, 2011 at 13:46

answered Jun 30, 2011 at 13:36

Grigor Gevorgyan

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Comments

Puppy · Accepted Answer · 2011-06-30 13:37:14Z

3

  if (counter = 1)

This does not compare counter and 1, it assigns 1 to counter and then checks counter- which we just set to 1 so it will always be positive and always be <= 10.

answered Jun 30, 2011 at 13:37

Puppy

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Comments

Itamar Katz · Accepted Answer · 2011-06-30 13:36:57Z

1

The line

if (counter = 1)

Should be

if (counter == 1)

since you want to compare, not to assign value.

answered Jun 30, 2011 at 13:36

Itamar Katz

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Comments

Nick Meyer · Accepted Answer · 2011-06-30 13:37:03Z

1

Your first example had

if (counter = 1)

instead of

if (counter == 1)

so the if statement would reset counter to 1 during each iteration.

answered Jun 30, 2011 at 13:37

Nick Meyer

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Comments

Nikolai Fetissov · Accepted Answer · 2011-06-30 13:37:50Z

0

Your problem is here:

if (counter = 1)

Assignment instead of comparison. Compile with higher warning level.

answered Jun 30, 2011 at 13:37

Nikolai Fetissov

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Comments

Klaim · Accepted Answer · 2011-06-30 13:38:06Z

0

if (counter = 1)

So, counter value is 1 forever.

answered Jun 30, 2011 at 13:38

Klaim

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Comments

StevieG · Accepted Answer · 2011-06-30 13:38:26Z

0

You're assigning 1 to counter rather than comparing it, use == instead of =

answered Jun 30, 2011 at 13:38

StevieG

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Comments

score 0 · Accepted Answer · 2011-06-30 13:44:21Z

0

As other notice, this is a common error. Your could avoid it by typing

if( 1 == counter )

instead of

if( counter == 1 )

since

if( 1 = counter )

would not compile (if you made the error and forgot an '=').

edited Jun 30, 2011 at 13:44

answered Jun 30, 2011 at 13:37

user153062

2 Comments

RobH Over a year ago

IIRC the Debian hack was implemented by changing an equality to an assignment. Since then, it may look backward, but I'm a big fan of constant-lvalue comparison.

David Hammen Over a year ago

Personal opinion, but I hate and loathe than construct. Compiling with warnings enabled will catch this particular error. Code analyzers will catch instances that the compiler won't catch such as if ((counter = 1)) ... Don't make me write things bass-ackwards.

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