this post was submitted on 16 Dec 2023
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Programming

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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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[–] mac@programming.dev 5 points 10 months ago* (last edited 10 months ago)

When the draw function calls itself it yields control to that new function its calling. When that function ends it takes back control and continues doing what it was doing.

This means all of the for loops in all of the functions will execute. Draw(1) will do the for loop and then return as it hits the end of the function (standard behaviour when you reach the end of a function even if theres no return statement). Then draw(2) will do the for loop as it gets back control now that draw(1) is done and then return, etc. all the way up

All parts of a function are recursive, theres no such thing as a non recursive part