C program to print hollow square or rectangle star pattern. 
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C Programming Language Loop control in C Language (Article) Loop control in C Language (Program)

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Program:

/**
 * C program to print hollow square star pattern
 */

#include <stdio.h>

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

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

    /* Iterate over each row */
    for(i=1; i<=N; i++)
    {
        /* Iterate over each column */
        for(j=1; j<=N; j++)
        {
            if(i==1 || i==N || j==1 || j==N)
            {
                /* Print star for 1st, Nth row and column */
                printf("*");
            }
            else
            {
                printf(" ");
            }
        }

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

    return 0;
}

Output:

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

Explanation:

Logic to print hollow square star pattern

 

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The above pattern is similar to square star pattern of N rows and N columns. Here star is printed only for first and last column or for first and last row.

Step by step descriptive logic to print empty square star pattern.

  1. Input number of rows to print from user. Store it in a variable say N.
  2. To iterate through rows, run an outer loop from 1 to N. For that define loop with structure for(i=1; i<=N; i++).
  3. To iterate through columns, run an inner loop from 1 to N. Define loop with structure for(j=1; j<=N; j++).
  4. Inside inner loop print star for first and last row or for first and last column. Which is print star if i==1or i==N or j==1 or j==N, otherwise print space.
  5. After printing all columns of a row, move to next line i.e. print a blank line after inner loop.

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