Creating just the border of a pyramid with asterisks in C

Question

OK. So I'm just trying to do some practice with simple algorithms and asterisks in C. This is not a homework problem. In my book there is a project that asks you to create a program that makes "these shapes" out of asterisks. One of them is a pyramid. While I can find numerous examples of how to make pyramid on the web, I can't find one that helps me figure out the algorithm for just the border of one. And I have not seen one on here either.

Now here is the code I have already.

#include <stdio.h>
int main(void)
{
    int i,j,k,x,h=0;
    printf("\n\n");

    for( i = 1; i <= 5; i++)
    {
        for( k = 1; k <=5-i; k++)
        {
            printf(" ");
        }
        for( j = 1; j <= 2*i-1; j++)
        {
            printf("*");
        }
        printf("\n");
    }
    for ( i = 6; i < 10; i++)
    {
        for( k = 1; k <= i-5; k++)
        {
            printf(" ");
        }
        for( j = 1; j <= i+1-3*h; j++)
        {
            printf("*");
        }
        printf("\n");
        h++;
    }
    printf("\n\n");

    return 0;
}

When you run the program it should, since I've ran it numerous times with no errors, give you this shape:

....*
...***
..*****
.*******
*********
.*******
..*****
...***
....*

I keep thinking that the loop that has the asterisk would probably need more loops to determine the location of the spacing between the asterisks. But I can't really begin to think of how to do this. What I want to end up with is this:

....*
...*.*
..*...*
.*.....*
*.......*
.*.....*
..*...*
...*.*
....*

Any help with this would be greatly appreciated. I am a beginner programmer. In my first University level programming class. We're only learning C in this class. We've learned up to Multidimensional Arrays, and started learning functions on Thursday.

Answer 1

Here is a hint. You want the "first and last *" - so look at the loop

for( j = 1; j <= 2*i-1; j++)
    {
        printf("*");
    }

And change it to something like:

printf("*");  // first *
for( j = 2; j<= 2*i-2; j++) printf(" "); // spaces until...
printf("*");  // last *

See how you get on with that… this is not the only place where you need to make this change.

EDIT in response to the request by @KalaJ I provide complete code - once with the first and last star, and once without. You can pick which one you want to use by changing the condition in the #if 0 preprocessor directive. If you set it to #if 1 you get the original pattern.

#include <stdio.h>
#if 0
int main(void)
{
    int i,j,k,x,h=0;
    printf("\n\n");

    for( i = 1; i <= 5; i++)
    {
        for( k = 1; k <=5-i; k++)
        {
            printf(" ");
        }
        printf("*");
        for( j = 2; j <= 2*i-2; j++)
        {
            printf(" ");
        }
        if(i>1) printf("*");
        printf("\n");
    }
    for ( i = 6; i < 10; i++)
    {
        for( k = 1; k <= i-5; k++)
        {
            printf(" ");
        }
        printf("*");
        for( j = 1; j <= i-3*h-1; j++)
        {
            printf(" ");
        }
        if(i<9) printf("*");
        printf("\n");
        h++;
    }
    printf("\n\n");

    return 0;
}
#else
int main(void)
{
    int i,j,k,x,h=0;
    printf("\n\n");

    for( i = 2; i <= 5; i++)
    {
        for( k = 1; k <=5-i; k++)
        {
            printf(" ");
        }
        printf("*");
        for( j = 2; j <= 2*i-2; j++)
        {
            printf(" ");
        }
        if(i>1) printf("*");
        printf("\n");
    }
    for ( i = 6; i < 9; i++)
    {
        for( k = 1; k <= i-5; k++)
        {
            printf(" ");
        }
        printf("*");
        for( j = 1; j <= i-3*h-1; j++)
        {
            printf(" ");
        }
        if(i<9) printf("*");
        printf("\n");
        h++;
    }
    printf("\n\n");

    return 0;
}
#endif

This produces either

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

or

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

Answer 2

1. Define each edge as a vector
2. find max(Y)
3. iterate from max(Y) down
4. for each Y find the matching X then print dots or star if you intersect a vector until max(X) on that line