Thread: While statements and loops

Hello all!
I'm currently working on a very basic program to draw a rectangle using asterisks, like so:

****
****
****
****

Not much point in it, but its all part of the learning process.

I'm trying to use while statements to get the program to draw the shape. I'm not sure if its the most efficient way of doing this but its working so far for me. At the moment I have 2 while statements which work fine, except when you run the program instead of making a rectangle my program makes this shape;

****
*
*
*

I figure its because my second while statement doesnt point back to my first one, or that I have to put the second while statement within the first. However all my attempts at this have been fruitless. If anyone could point me in the right direction it'd be much appreciated!

Thank you!

Native

Code:

#include <stdio.h>
#include <math.h>

int main(int argc, char *argv[])
{
        int width = 0;
        int height = 0;

        printf("Please enter a width and height seperated by a comma\n");
        scanf("%d,%d",&width,&height);


        while (width>0)
        {
                printf("*");
                width--;
        }

        while (height>0)
        {
                printf("*\n");
                height--;
        }
}

Well I thought maybe this would work, but still not happening. I've also noticied my program is printing one too many dots horizontally '>_<'

Code:

        while (width>0)
        {
                printf("*");
                width--;
         
                while (height>0)
                {
                        printf("*\n");
                        height--;
                }
        }

Consider what height will start out at the second time through the outer (width) loop. You're missing one small detail the way it is now.

Well I have tried everything possible (examples below) and I cannot get this thing working - I know you guys are trying to help by hinting at what to do but honestly I've gotten this far already but I cannot see what is wrong..... :/

Code:

  while (width>0)
        {
                printf("*");
                width--;
         
                while (height>0)
                {
                        printf("*\n");
                        height--;
                }
        }

Code:

  while (height>0)
        {
                printf("*");
                height--;
         
                while (width>0)
                {
                        printf("*\n");
                        width--;
                }
        }

Code:

  while (height>0)
        {
                printf("*\n");
                height--;
         
                while (width>0)
                {
                        printf("*");
                        width--;
                }
        }

Code:

while (width>0)
        {
                printf("*");
                width--;

                if (width=0) 
                {
                        printf("\n");
                 
                        while (height>0)
                        {
                                printf("*");
                                height--;
                        }
                }
        }

Also, it might be clearer with for loops instead.

Code:

int width = 20;
int height = 10;
int w, h;

for(w = 0;w < width;++w)
{
  for(h = 0;h < height;++h)
    putchar('*');
  putchar('\n');
}

Originally Posted by Native

Does that section set twidth to equal width so that wheen the 2nd part of the loop is completed it references back to width which is still at its original value?

Correct. When the inner loop graduates, the outer loop moves to it's next iteration, the function reassigns twidth to width. Since width is now untouched it's getting the same value every time. In your original attempts you were altering the value of width... which would be reflected in the next iteration of your loop.

As an exercise in understanding you should sit with paper and pencil and work out the steps that are executed, with the values of each variable at each step... it will become much clearer.

Also you should try to do it with the loops counting up from 0... it will require different exit conditions in your loops and will provide you with an interesting look at different ways to do the same thing.

As an optimization you can change var = var - 1; to var--; which gives you the same result. The -- is C shorthand for subtract 1... ++ adds 1. But it's also a little bit faster (not that speed really matters here)