this post was submitted on 16 Dec 2023
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Programming

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32
Why does the for loop repeat in this recursion? (lemm.ee)
submitted 10 months ago by milon@lemm.ee to c/programming@programming.dev
30 comments fedilink hide all child comments
 

I used the debugger to examine this code but not understanding a couple areas.

  1. Why does the for loop repeat after it exits to print a new line? If it exits the loop, shouldn't it be done with it?
  2. Why is n incremented and not i as stated with i++?

int main(void)
{
    int height = get_int("Height: ");

    draw(height);
}

void draw(int n)
{
    if (n <= 0)
    {
        return;
    }

    draw(n - 1);

    for (int i = 0; i < n; i++)
    {
        printf("#");
    }
    printf("\n");
}
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[–] anton@lemmy.blahaj.zone 5 points 10 months ago

Recursion is often unintuitive for beginners, to understand this code we should simply it a bit


int main(void)
{
    int height = get_int("Height: ");

    draw(height);
}

void draw(int n)
{
    if (n <= 0)
    {
        return;
    }

    draw(n - 1);
    printf("%d",  n);
    
    printf("\n");
}

Inputting 3 should now give us a output like

1
2
3

Try to understand that case first and than muddle it up with the loop.

If you examine it in a debugger look at the Stack trace. If you use gdb its bt in a visual debugger it's probably the list of function names next to the variables