Inverted Alphabet Pattern (ABCDE to A) in PHP

Beginner
⏱️ 6 min read
📚 Updated: Aug 2025
🎯 2 Code Examples
Decreasing rows
Inverted alphabet pattern output ABCDE, ABCD, ABC, AB, A in PHP programming

What You'll Learn

This PHP program prints an inverted alphabet triangle: the first row is the longest and each next row removes the last letter.

For rows = 5, the output is ABCDE, ABCD, ABC, AB, A.

⭐ Pattern Output

When you run the program with rows = 5:

Output
ABCDE
ABCD
ABC
AB
A
1

Complete PHP Program

Fixed rows = 5 version:

PHP
<?php
$rows = 5;
$alpha = range('A', 'Z');

for ($i = $rows - 1; $i >= 0; $i--) {
    for ($j = 0; $j <= $i; $j++) {
        echo $alpha[$j];
    }
    echo PHP_EOL;
}

🧠 How It Works

1

Alphabet array

$alpha = range('A', 'Z'); gives letters A..Z in an array.

Setup
2

Outer loop shrinks the row length

for ($i = $rows - 1; $i >= 0; $i--) counts down, so each next row prints fewer letters.

Decreasing
3

Inner loop prints from A each time

The inner loop always starts at 0 (A) and prints up to $i, producing ABCDE, then ABCD, then ABC, and so on.

Prefix
=

Inverted triangle

Total printed letters are still n(n+1)/2, so runtime is O(n²) for n rows.

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 (max 26): ";
$rows = (int) trim(fgets(STDIN));
$rows = max(1, min($rows, 26));

$alpha = range('A', 'Z');

for ($i = $rows - 1; $i >= 0; $i--) {
    for ($j = 0; $j <= $i; $j++) {
        echo $alpha[$j];
    }
    echo PHP_EOL;
}

💡 Tips for Enhancement

Try These

  • Compare with Program 1 (growing rows)
  • Switch to lowercase using range('a', 'z')
  • Right-align the triangle using leading spaces
  • Print only even-length rows for another variation
  • Try a hollow version by printing only the first and last letters

Avoid

  • Using <br> in CLI examples (use PHP_EOL)
  • Allowing $rows > 26 without handling wrap-around
  • Off-by-one errors ($i and $j bounds matter)
  • Mixing HTML output with CLI output without intent

Key Takeaways

1

Use a decreasing outer loop so the number of printed letters shrinks each row.

2

The inner loop always starts from A, so each line is a prefix.

3

This is an inverted version of Program 1 (only the outer loop direction changes).

4

Total printed letters are \(n(n+1)/2\), so runtime is O(n²).

❓ Frequently Asked Questions

Program 1 grows: A, AB, ABC, ... up to ABCDE. This program shrinks: ABCDE, ABCD, ABC, ... down to A.
For letters, str_repeat doesn’t help directly. You can build each row using substrings (e.g., join letters then take a prefix), but nested loops are the clearest for beginners.
It’s O(n²) for n rows, because the program prints 1+2+…+n letters in total.

Next: PHP Alphabet Pattern 6

Continue to Program 6 for the next alphabet pattern in PHP.

Program 6 →
Did you know?

You can convert the growing version (Program 1) into this inverted version by only changing the direction of the outer loop.

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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