C Program to Print Hollow Right-Angled Triangle

Introduction

A hollow right-angled triangle consists of stars (*) along the boundary of the triangle, with the interior filled with spaces. This pattern helps in understanding how to use loops and conditional statements to control the printing of stars and spaces.

Problem Statement

Create a C program that:

• Accepts the number of rows for the triangle.
• Prints a hollow right-angled triangle pattern using stars (*).

Example:

• Input: rows = 5
• Output:

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

Solution Steps

1. Input the Number of Rows: The size determines how many rows the triangle will have.
2. Use Nested Loops: The outer loop controls the rows, and the inner loop controls the printing of stars and spaces.
3. Conditionally Print Stars: Stars are printed at the boundary (first row, last row, and first and last columns), while spaces are printed inside to create the hollow effect.

C Program

#include <stdio.h>

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

    // Step 1: Accept the number of rows for the triangle
    printf("Enter the number of rows: ");
    scanf("%d", &rows);

    // Step 2: Outer loop for rows
    for (i = 1; i <= rows; i++) {
        // Step 3: Inner loop for columns
        for (j = 1; j <= i; j++) {
            // Step 4: Print stars at the boundary or at the first or last column of each row
            if (i == rows || j == 1 || j == i) {
                printf("*");
            } else {
                printf(" ");  // Print spaces inside the triangle
            }
        }
        // Move to the next line after each row
        printf("\n");
    }

    return 0;
}

Explanation

Step 1: Input Number of Rows

• The program starts by asking the user for the number of rows to print the hollow right-angled triangle.

Step 2: Outer Loop for Rows

• The outer loop controls the number of rows printed, running from 1 to rows.

Step 3: Inner Loop for Columns

• The inner loop controls the number of columns (stars) printed for each row.

Step 4: Conditional Printing

• Stars (*) are printed at the boundary:
  • On the first row (i == 1),
  • On the last row (i == rows),
  • At the first column (j == 1),
  • At the last column of each row (j == i).
• Spaces are printed for the inside of the triangle, creating the hollow effect.

Output Example

For rows = 5, the output will be:

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

For rows = 6, the output will be:

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

Conclusion

This C program prints a hollow right-angled triangle pattern using stars (*). The program uses nested loops and conditional logic to print stars along the boundary of the triangle while leaving the interior hollow. This exercise is useful for understanding loop control and conditional printing in C programming.