C program to print hollow diamond star pattern 
**********
****  ****
***    ***
**      **
*        *
*        *
**      **
***    ***
****  ****
**********

C Programming Language Loop control in C Language (Article) Loop control in C Language (Program)

1485

Program:

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

#include <stdio.h>

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

    printf("Enter value of n : ");
    scanf("%d", &n);

    // Loop to print upper half of the pattern
    for(i=1; i<=n; i++)
    {
        for(j=i; j<=n; j++)
        {
            printf("*");
        }

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

        for(j=i; j<=n; j++)
        {
            printf("*");
        }

        printf("\n");
    }

    // Loop to print lower half of the pattern
    for(i=1; i<=n; i++)
    {
        for(j=1; j<=i; j++)
        {
            printf("*");
        }

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

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

        printf("\n");
    }

    return 0;
}

Output:

Enter value of n : 5
**********
****  ****
***    ***
**      **
*        *
*        *
**      **
***    ***
****  ****
**********

Explanation:

Required knowledge

Basic C programming, For loop, Nested loop

Must know - Program to print diamond star pattern

Logic to print hollow diamond star pattern

The pattern seems to be one of the complex pattern to think. To make it easier, let us bisect in two halves.

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

Here in the upper part of the pattern, trailing and leading stars are inverted right triangle pattern that can be easily printed. Each row contains 2*rownumber - 2 spaces.

Moving on to the second half, if you look at the trailing and leading stars you will find that both of them are right triangle star pattern and total number of spaces per row is 2*rownumber - 2.

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