#include <stdio.h>
int main()
{
    int i, j;
    for (i = 1; i <= 7; i++)
    {
        for (j = 1; j <= 7 - i; j++)
        {
            printf(" ");
        }
        for (j = 1; j <= i; j++)
        {
            printf("* ");
        }
        printf("\n");
    }
    for (i = 6; i >= 1; i--)
    {
        for (j = 1; j <= 6 - i; j++)
        {
            printf(" ");
        }
        for (j = 1; j <= i; j++)
        {
            printf(" *");
        }
        printf("\n");
    }
}

codeaft@codeaft:~$ gcc codeaft.c
codeaft@codeaft:~$ ./a.out
      * 
     * * 
    * * * 
   * * * * 
  * * * * * 
 * * * * * * 
* * * * * * * 
 * * * * * *
  * * * * *
   * * * *
    * * *
     * *
      *
codeaft@codeaft:~$