JavaScript Program to Print Right-Angled Triangle Pattern

Introduction

A right-angled triangle pattern consists of stars (*) arranged in a triangular shape, where each row contains an increasing number of stars starting from 1. This is a simple yet useful exercise to practice using loops and formatting in JavaScript.

Problem Statement

Create a JavaScript program that:

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

Example:

• Input: rows = 5
• Output:

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

Solution Steps

1. Input the Number of Rows: The user specifies how many rows the triangle should have.
2. Use Nested Loops: The outer loop handles the rows, and the inner loop handles printing the stars.
3. Display the Right-Angled Triangle: Print an increasing number of stars for each row.

JavaScript Program

// Step 1: Input the number of rows for the triangle
let rows = parseInt(prompt("Enter the number of rows: "));

// Step 2: Outer loop for rows
for (let i = 1; i <= rows; i++) {
    let output = '';
    
    // Step 3: Inner loop to print stars for each row
    for (let j = 1; j <= i; j++) {
        output += '*';
    }
    
    // Print the output for the current row
    console.log(output);
}

Explanation

Step 1: Input the Number of Rows

• The program starts by asking the user to input the number of rows for the right-angled triangle. This input is converted to an integer using parseInt().

Step 2: Outer Loop for Rows

• The outer loop controls how many rows are printed. It runs from 1 to rows, where each iteration represents a row.

Step 3: Inner Loop for Stars

• The inner loop controls the number of stars (*) printed for each row. The number of stars printed increases with each row (i).

Step 4: Output the Row

• After constructing the row with stars, it is printed using console.log().

Output Example

For rows = 5, the output will be:

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

For rows = 4, the output will be:

*
**
***
****

Conclusion

This JavaScript program prints a right-angled triangle star pattern using nested loops. The number of stars increases with each row, creating a right-angled triangle shape. This exercise helps in practicing loop control and output formatting in JavaScript.