Weird output printing arrays in C

Question

I decided to do the CS50 course again and tried to go about solving some of the problems differently. There is a task where you have to print pyramids with two spaces between each half using the '#' char with a height determined by the user (should be between 1 and 8 though). If the height was 4 it should look like this for example:

   #  #
  ##  ##
 ###  ###
####  ####

This works fine when the integer is anything between 1 and 7 but when it is 8 it starts adding gibberish non-ascii characters to the right of the left half of the pyramid.

This is my code:

int main(void)
{
    int h = 0;
    while (h < 1 || h > 8) {
        printf("Height: ");
        scanf("%d", &h);
    }

    for (int i = 0; i < h; i++) {
        char a[h + 1];
        char b[h - (h - i) + 2];
        for (int j = 0; j < h; j++) {

            a[j] = h - j > i + 1 ? ' ': '#';
            if (i <= j) b[i] = '#';
        }
        printf("%s  %s\n", a, b);
    }
}

I thought it might be a memory thing so I just set the size of the char arrays to 3000. It stopped printing gibberish and still worked fine for heights 1 - 7 but when the user put anything more than 7 the pyramid looked skewed like this:

          #
       #  ##
      ##  ###
     ###  ####
    ####  #####
   #####  ######
  ######  #######
 #######  ########

Why is this happening and how can I fix it?

Thank you to everyone who responded! The problem was that I didn't set null terminators in the string. This is the working function:

int main(void)
{
    int h = 0;
    while (h < 1 || h > 8) {
        printf("Height: ");
        scanf("%d", &h);
    }

    for (int i = 0; i < h; i++) {
        char a[h + 1];
        char b[h - (h - i) + 2];
        for (int j = 0; j < h; j++) {

            a[j] = h - j > i + 1 ? ' ': '#';
            if (i <= j) b[i] = '#';
        }
        a[h] = '\0';
        b[h - (h - i) + 1] = '\0';
        printf("%s  %s\n", a, b);
    }
}

Answer 1

It looks like there are few issues with your code.

1. You are initializing arrays a and b inside the loop. This means that the arrays are created with different sizes for each iteration, causing unpredictable behavior.
2. When you print the arrays using %s, it expects null-terminated strings. However, the arrays a and b might not be null-terminated. To fix this, you can modify your code to use a single array for each row and adjust the printing logic. Try the below code:

#include <stdio.h>
int main(void) {
    int h = 0;
    while (h < 1 || h > 8) {
        printf("Height: ");
        scanf("%d", &h);
    }

    for (int i = 0; i < h; i++) {
        char row[2 * h + 3];  // Maximum required size for the row

        for (int j = 0; j < 2 * h + 2; j++) {
            if (j < h - i || (j >= h && j < h + 2) || j > h + i + 1) {
                row[j] = ' ';
            } else {
                row[j] = '#';
            }
        }
        row[2 * h + 2] = '\0';  // Null-terminate the string
        printf("%s\n", row);
    }

    return 0;
}