Inverted Right-Angled Triangle Star Pattern in PHP

Beginner
⏱️ 6 min read
📚 Updated: Aug 2025
🎯 2 Code Examples
n rows total
Inverted right-angled triangle star pattern output in PHP programming

What You'll Learn

This program prints an inverted right-angled triangle where each next row contains one less star than the previous row.

Row i prints exactly i stars while i decreases from rows to 1.

⭐ 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 <= $i; $j++) {
        echo "*";
    }
    echo PHP_EOL;
}

🧠 How It Works

1

Setup

$rows sets the first line width. for ($i = $rows; $i >= 1; $i--) counts down so the widest row prints first.

Setup
2

Stars: echo "*"

for ($j = 1; $j <= $i; $j++) prints $i asterisks on one line.

Inner
3

New line

echo PHP_EOL; ends the row before $i changes. Variation: echo str_repeat("*", $i) . PHP_EOL;.

Line break
=

Inverted triangle

Total stars still n(n+1)/2 — O(n²) time, O(1) extra space. The widest line scrolls horizontally in the green preview on small screens.

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 <= $i; $j++) {
        echo "*";
    }
    echo PHP_EOL;
}

💡 Tips for Enhancement

Try These

  • Print Program 1 (upright triangle) to compare both shapes
  • Validate that $rows > 0 before printing
  • Use str_repeat("*", $i) to print each row without an inner loop
  • Add spaces between stars for visual variety
  • Create a hollow inverted triangle (print only border stars)

Avoid

  • Forgetting the newline after each row
  • Assuming CLI input is always valid
  • Mixing HTML output with CLI output in the same script without intent
  • Off-by-one errors in loop bounds (>= 1 matters)
  • Over-complicating a simple pattern (keep it readable)

Key Takeaways

1

Outer loop starts from rows and goes down to 1, so the triangle shrinks each row.

2

Row i prints exactly i stars, so the widest row comes first.

3

Total stars are n(n + 1)/2, so time complexity is O(n²).

4

This is the mirror of Program 1 and helps you practice decrementing loops.

5

For CLI programs, fgets(STDIN) is a simple way to read input.

❓ Frequently Asked Questions

The outer loop runs from $i = $rows down to 1. For each row $i, the inner loop runs from $j = 1 to $i, printing one star per iteration. So the first row prints $rows stars and each next row prints one less.
Yes. For each row $i, you can print str_repeat("*", $i). This often makes the code shorter and easier to read.
The time complexity is O(n²) where n is the number of rows, because the total number of printed stars is \(1+2+\dots+n = n(n+1)/2\).
In a web app you can read from $_GET or $_POST. For example: $rows = (int)($_GET["rows"] ?? 5);. This tutorial uses CLI input because it matches common pattern-printing exercises.

Next: Right-Aligned Triangle

Continue to Program 3 to print the right-aligned star triangle pattern in PHP.

Program 3 →
Did you know?

This is the mirror of Program 1. Practicing both helps you master loop bounds and makes it easier to build larger patterns like pyramids and diamonds.

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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