Why simple program for printing out dividers of the input number stopped working?

Question

here is the code I am having an issue with:

int printDividers(int x)
{
    for (int j=0; j<x+1; j++)
    {
        if (x%j==0) cout << j << ", ";
    }
}

int main()
{
    int z;
    cout << "Enter a number and the program will print out it's dividors:" << endl;
    cin >> z;
    printDividers(z);

    return 0;
}

After entering your number it says main.exe stopped working. I haven't figured out why, I can't spot the error in the code.

Have you tried debugging your code? Could you give an example of the input that you used to get this issue? — John Odom, Dec 16 '15 at 16:16
I wonder if code compiles since `int printDividers(int x)` doesn't returns anything — Angelus Mortis, Dec 16 '15 at 16:18
@JohnOdom I am using CodeBlocks and it says there are no errors. It always crashes, no matter which number you enter. For example 5, or 53, or 7546... Nothing works. — Blank空白, Dec 16 '15 at 16:18
You need to return something from your function or make it `void`. — NathanOliver, Dec 16 '15 at 16:18
@MathewsMathai That is normal from `main`, indicating successful completion of the program. — BoBTFish, Dec 16 '15 at 16:20
Some errors, like the one pointed out by CompuChip, are only exposed at runtime — Leeor, Dec 16 '15 at 16:20
Has it stoped working, or was it just never working at all? *philosophical* — dhein, Dec 16 '15 at 16:22
@NathanOliver could you give me an example of what could I return in this function and how should I change the main program so it would work the same? — Blank空白, Dec 16 '15 at 16:22
@coincoin I am new to programming and that's why this my seem dumb... — Blank空白, Dec 16 '15 at 16:23

score 4 · Answer 1 · edited Dec 16 '15 at 16:24

4

When i==0, we will run the test if (x%0 == 0) which isn't a valid statement because it attempt to divide by 0. Hence, your program ~~will~~ might crash. Its behavior is undefined

edited Dec 16 '15 at 16:24

dhein

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answered Dec 16 '15 at 16:20

Danh

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1

*Might* crash. The behaviour is undefined. – Bathsheba Dec 16 '15 at 16:22
Thanks. I edited. I'm using my mobile, so, I don't have the standard to reference – Danh Dec 16 '15 at 16:24
@Danh I changed the stil of your change. I hope thats what you tryed to achieve. – dhein Dec 16 '15 at 16:25
Yes, exactly what I want to change – Danh Dec 16 '15 at 16:26

Bathsheba · Answer 2 · 2015-12-16T17:56:17.677

4

You're out of luck, you are attempting to compute % 0 in your for loop. Along with integral division by zero, the behaviour on doing this is undefined:

The C++03 Standard states in §5.6/4,

[...] If the second operand of / or % is zero the behavior is undefined; [...]

edited Dec 16 '15 at 17:56

answered Dec 16 '15 at 16:20

Bathsheba

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To quote HACK3R's(?) comment who sadly is not registred here anymore: [Standard quotation == automatic +1](http://stackoverflow.com/a/18416748/2003898) – dhein Dec 16 '15 at 16:26
So dividing by zero is a no-go. Thank you! – Blank空白 Dec 16 '15 at 16:28
1

Only for integral types. Floating point division by zero *is* defined. But I'd still advise against it. – Bathsheba Dec 16 '15 at 16:29

Fantastic Mr Fox · Accepted Answer · 2015-12-16T16:38:36.240

2

What is x % 0? (Answer: Undefined Behaviour) This is what causes your run-time error.

Change to this:

for (int j=1; j<x+1; j++)

http://ideone.com/K5vSxt

edited Dec 16 '15 at 16:38

answered Dec 16 '15 at 16:21

Fantastic Mr Fox

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Why simple program for printing out dividers of the input number stopped working?

3 Answers3