Inverted Right-Aligned Triangle Star Pattern in PHP

Beginner
⏱️ 6 min read
📚 Updated: Aug 2025
🎯 2 Code Examples
Spaces + stars
Inverted right-aligned triangle star pattern output in PHP programming

What You'll Learn

This program prints an inverted right-aligned triangle. The first row prints rows stars, and each next row prints one less star, while leading spaces increase to keep the right edge aligned.

For row $i (from $rows down to 1), print $rows - $i spaces and then print $i stars.

⭐ Pattern Output

When you run the program with rows = 5:

Output
*****
 ****
  ***
   **
    *
1

Complete PHP Program

Fixed rows = 5 version:

PHP
<?php
$rows = 5;

for ($i = $rows; $i >= 1; $i--) {
    for ($j = 1; $j <= $rows - $i; $j++) {
        echo " ";
    }
    for ($k = 1; $k <= $i; $k++) {
        echo "*";
    }
    echo PHP_EOL;
}

🧠 How It Works

1

Setup

$rows is the height. for ($i = $rows; $i >= 1; $i--) starts with the widest row ($i == $rows) and ends at one star.

Setup
2

Padding: echo " "

for ($j = 1; $j <= $rows - $i; $j++) prints $rows - $i spaces. On the first row that count is zero; it grows as $i shrinks.

Right align
3

Stars: echo "*"

for ($k = 1; $k <= $i; $k++) prints $i stars after the padding.

Stars
4

New line

echo PHP_EOL; ends each row. Characters before the newline: ($rows - $i) + $i = $rows every time.

Line break
=

Inverted right-aligned triangle

Star total n(n+1)/2; O(n²) output for n = $rows, O(1) extra space. Wide rows scroll horizontally in the green preview on phones.

2

Variation — User Input (CLI) Version

Read rows from standard input (works when you run the file from terminal using php):

PHP
<?php
echo "Enter the number of rows: ";
$rows = (int) trim(fgets(STDIN));

for ($i = $rows; $i >= 1; $i--) {
    for ($j = 1; $j <= $rows - $i; $j++) {
        echo " ";
    }
    for ($k = 1; $k <= $i; $k++) {
        echo "*";
    }
    echo PHP_EOL;
}

💡 Tips for Enhancement

Try These

  • Compare with Program 3 to see how reversing the outer loop changes the shape
  • Print a centered inverted pyramid by switching to odd stars + more spaces
  • Print a hollow version (stars only on the borders)
  • Use a different character (like #)
  • Validate that $rows > 0

Avoid

  • Forgetting that spaces increase as stars decrease (alignment breaks)
  • Off-by-one errors in the space loop ($rows - $i)
  • Mixing tabs and spaces (output alignment changes)
  • Skipping newline after each row
  • Assuming input is valid without checking

Key Takeaways

1

Inverted right-aligned = print ($rows - $i) spaces, then $i stars, with $i decreasing.

2

The outer loop runs backward ($rows to 1) to shrink the star count each row.

3

Spaces increase by 1 each row, keeping the right edge aligned.

4

Time complexity is O(n²) for n rows.

5

This pattern is a stepping stone to centered inverted pyramids and diamond shapes.

❓ Frequently Asked Questions

Spaces are printed first to push the stars to the right side. As the star count decreases, the space count increases so the right edge remains aligned.
Use an outer loop that increases from 1 to $rows (Program 3). The space loop stays $rows - $i, but stars become $i as $i increases.
It’s O(n²) for n rows because each row prints about n characters (spaces + stars) and there are n rows.

Next: Pyramid Pattern

Continue to Program 5 to print a centered pyramid star pattern in PHP.

Program 5 →
Did you know?

Right-aligned patterns are excellent practice before moving to centered pyramids, because both require printing spaces and stars with the correct counts.

About the author

Mari Selvan M P
Mari Selvan M P 🔗

Developer, cloud engineer, and technical writer

  • Experience 12 years building web and cloud systems
  • Focus Full Stack Development, AWS, and Developer Education

I write practical tutorials so students and working developers can learn by doing—from databases and APIs to deployment on AWS.

AWS Certified Developer – Associate (Credly)

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