Python Program to Print Hollow Triangle Star Pattern

Introduction

A hollow triangle star pattern consists of stars (*) forming the boundary of a right-angled triangle, while the inside of the triangle is left hollow (filled with spaces). This pattern is a great way to practice using loops and conditional logic in Python.

Problem Statement

Create a Python program that:

• Accepts the number of rows for the triangle.
• Prints a hollow right-angled triangle star pattern.

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 controls the rows, and the inner loop handles printing stars and spaces.
3. Conditionally Print Stars: Stars are printed along the boundary (first row, last row, and the first and last columns of each row), while spaces are printed inside to create the hollow effect.

Python Program

# Step 1: Input the number of rows for the hollow triangle
rows = int(input("Enter the number of rows: "))

# Step 2: Outer loop for rows
for i in range(1, rows + 1):
    # Step 3: Inner loop for columns
    for j in range(1, i + 1):
        # Step 4: Print stars at the boundary
        if i == rows or j == 1 or j == i:
            print("*", end="")
        else:
            print(" ", end="")
    # Move to the next line after each row
    print()

Explanation

Step 1: Input the Number of Rows

• The program begins by asking the user for the number of rows for the hollow triangle.

Step 2: Outer Loop for Rows

• The outer loop controls how many rows are printed. It runs from 1 to rows.

Step 3: Inner Loop for Columns

• The inner loop controls the number of columns printed for each row. It runs from 1 to i (where i is the current row number).

Step 4: Conditional Printing

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

Output Example

For rows = 5, the output will be:

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

For rows = 6, the output will be:

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

Conclusion

This Python program prints a hollow right-angled triangle star pattern using nested loops and conditional logic. The stars are printed along the boundary of the triangle, while spaces are printed inside to create the hollow effect. This exercise helps in practicing loop control and conditional statements in Python.