problem with do loop and if statement

This is a discussion on problem with do loop and if statement within the C++ Programming forums, part of the General Programming Boards category; I'm trying to get a number of rooms and it can't be less than 1. I have this do loop ...

  1. #1
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    problem with do loop and if statement

    I'm trying to get a number of rooms and it can't be less than 1. I have this do loop with and if statement but when i enter invalid input it just outputs invalid output and goes onto my next function.

    Code:
    int num_of_rooms()
    {
    	int num_rm, valid = 1;
        
    	do
    	{
    	cout << "Enter the number of rooms: ";
    	cin >> num_rm;
    
    	if (num_rm < 1)
    		{
    		valid = 0;
    		cout << "Invalid input\n";
    		}
    	}while(valid = 0);
    
    	return num_rm;
    }

  2. #2
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    Might be that 'while (valid = 0)' should have 2 ='s ('while (valid == 0)'). Also just so you know, if the first time you input less than one, it will never break from the loop because 'valid' will never change.

  3. #3
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    Also, since you're using valid like a boolean, you may as well make it a bool.
    It is too clear and so it is hard to see.
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  4. #4
    and the hat of wrongness Salem's Avatar
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    > while(valid = 0)
    This makes it false, even if it's still true!

    Compare, don't assign.

    Making it a bool variable would help, then you can just say
    while ( !valid )
    If you dance barefoot on the broken glass of undefined behaviour, you've got to expect the occasional cut.
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  5. #5
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    Quote Originally Posted by Salem View Post
    Making it a bool variable would help, then you can just say
    while ( !valid )
    Even if it's not bool, the expression (!valid) evaluates correctly for checking if the value is zero (or NULL for that matter). Otherwise backwards compatibility with C would be broken.

    I agree that the variable should be bool, since the "valid" variable only holds two possible values: true or false. This helps indicating the correct use of the variable. [It makes sure no-one thinks it's "the number of valid entries" or some such].

    --
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