4

I'm going through the Harvard CS50 online course and one of the problems is to create a "mario style pyramid" using spaces and hashes. I've got the spaces solved but the hashes are giving me trouble. Here's the code:

#include <stdio.h>
#include <cs50.h>

int main(void)
{
    //get height between 1 and 23
    int height;
    do
    {
        printf("Please enter a height: ");
        height = GetInt();
    }
    while (height < 1 || height > 23);

    //build pyramid
    for (int i = 0; i < height ; i++)
    {
        //add spaces
        for (int space = height - 1 - i; space >= 0; space--)
            printf(" ");

        //add hashtags
        for (int hash = 2 + i; hash <= height; hash++)
            printf("#");

        printf("\n");
    }
}

When i run it in the terminal with a height of 5 i'm getting this: 

     ####
    ###
   ##
  #
   <-- space here also

when i want this:

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

Any feedback would be appreciated, thanks

Raktim Biswas
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roncook
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    If you look at the other questions tagged CS50, there are numerous ones tussling with this same problem — maybe one of those Q&A will help. Enter `[cs50] mario` into the search box. – Jonathan Leffler Aug 15 '16 at 19:18
  • you're confusing yourself with the opposing loops. one decreasing, one increasing. just go with two increasing loops. second one (hashes) bases itself on how many spaces were output in the first one. – Marc B Aug 15 '16 at 19:19
  • For myself I'd use a single loop and a local constant initialised with 21 spaces followed by 23 hashes (SO won't let me paste itas it compresses the spaces) I'll leave the details for the reader :) That won't give you a pyramid, but a ramp – kdopen Aug 15 '16 at 19:21
  • Going along with what [Jonathan Leffler](http://stackoverflow.com/users/15168/jonathan-leffler) commented, take a look at [this question](http://stackoverflow.com/q/20182057/4520911) – iRove Aug 15 '16 at 19:23

1 Answers1

6

Just try it with the following code:

int main(void)
{
    int height;
    printf("Please enter a height: ");
    scanf("%d", &height);

    //build pyramid
    for (int i = height; i >= 1; i--)
    {
        //add spaces
        for (int space = 1; space < i; space++)
            printf(" ");

        //add hashtags
        for (int hash = height; hash >= i-1; hash--)
            printf("#");

        printf("\n");
    }
}

when the value of height is 5, you get the desired output:

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

See the Working Fiddle.

In your code, when the value of i is 0 in:

for (int i = 0; i < height ; i++)
         ^^^^^^

the other loops executes as follows:

for (int space = height - 1 - i; space >= 0; space--)
    printf(" ");

here, the loop initializes space = 4 (when height is 5) and the loop condition is valid till space >= 0, so it prints the first 4 characters as " ".

And, Finally when it comes to this loop:

for (int hash = 2 + i; hash <= height; hash++)
    printf("#");

here, the loop initializes hash = 2 (i was 0 in the first loop, remember that?) and the loop conditions continues till hash <= height. So, it prints the next 4 characters as "#" as the above condition evaluates to 2,3,4,5 in:

(int hash = 2; hash <= 5; hash++)
           ^^^        ^^^

and the rest of the code carries on and produces the output as:

     ####
    ###
   ##
  #

If you are able to understand the above logic, then you'd be able to decode my solution as well :)

Raktim Biswas
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