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");
}
  • xmunk
    6·
    1 year ago

    So you’re drawing a triangle of # that starts skinny in the top left and grows to the right with a height and width of n?

    As an example, Height 3 would be:

    #
##
###

    I’m not following your questions, but the code seems pretty reasonable… though the use of recursion feels pretty unnecessary when you could easily just use a nested for loop.

    • xmunk
      7·
      1 year ago

      An example using a nested loop

      $n = 3;

for ($i = 0; $i <= $n; $i++) {
    for ($j = 0; $j < $i; $j++) {
        echo '#';
    }
    echo "\n";
}

      https://3v4l.org/e0IJm

    • milon@lemm.eeOP
      2·
      1 year ago

      It’s supposed to be a pyramid but not my code. It’s an example of a recursive function from a CS50 lecture and I’m just trying to understand how the code works line by line.

      • xmunk
        2·
        1 year ago

        So is my example of Height 3 in line with your expectations?

          • xmunk
            2·
            1 year ago

            I wrote an equivalent version just using nested loops - reading it might help you understand why the recursion works the way it does.

            • milon@lemm.eeOP
              1·
              1 year ago

              Thanks. I did see that. I have a general understanding of how recursion works I think where the function calls itself again and again but I don’t get why the code (for loop) below the draw(n - 1) is recursive.

              • xmunk
                5·
                1 year ago

                The code below the draw(n - 1) isn’t recursive… the call to draw(n - 1) is the recursion.

                Sometimes, it can be helpful to invert recursion. Think about what draw(0) would be and write it down… then compute draw(1) using the value you previously computed for draw(0).