C program to print hollow pyramid (Equilateral triangle) star pattern 
    *
   * *
  *   *
 *     *
*********

C Programming Language / Loop control in C Language

1743

Program:

/**
 * C program to print hollow pyramid triangle star pattern
* atnyla.com
 */

#include <stdio.h>

int main()
{
    int i, j, rows;

    /* Input rows to print from user */
    printf("Enter number of rows : ");
    scanf("%d", &rows);

    for(i=1; i<=rows; i++)
    {
        /* Print trailing spaces */
        for(j=i; j<rows; j++)
        {
            printf(" ");
        }

        /* Print hollow pyramid */
        for(j=1; j<=(2*i-1); j++)
        {
            /*
             * Print star for last row (i==rows),
             * first column(j==1) and for
             * last column (j==(2*i-1)).
             */ 
            if(i==rows || j==1 || j==(2*i-1))
            {
                printf("*");
            }
            else
            {
                printf(" ");
            }
        }

        /* Move to next line */
        printf("\n");
    }

    return 0;
}

Output:

Enter number of rows: 5
    *
   * *
  *   *
 *     *
*********

Explanation:

Required knowledge

Basic C programming, If else, For loop, Nested loop

Logic to print hollow pyramid star pattern

 

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

 

The above pattern is similar to pyramid star pattern except of center spaces.

Step by step descriptive logic to print hollow pyramid star pattern.

  1. Input number of rows to print from user. Store it in a variable say rows.
  2. To iterate through rows run an outer loop from 1 to rows. The loop structure should look like for(i=1; i<=rows; i++).
  3. To print spaces, run an inner loop from i to rows - 1. The loop structure should look like for(j=i; j<rows; j++). Inside this loop print single space.
  4. To print star, run another inner loop from 1 to i * 2 - 1. The loop structure should look like for(j=1; j<=(i*2-1); j++). Inside this loop print star for ith or last column or for last row.
  5. After printing all columns of a row, move to next line i.e. print new line.

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