Why does the pattern read A, then B C, then D E F?

A single counter k starts at A and increments after every printed character. Row 1 prints one letter, row 2 prints the next two, row 3 prints the next three, and so on.

Why is the counter incremented inside the inner loop?

Each inner-loop iteration prints exactly one new letter. Incrementing once per row would not advance the alphabet fast enough for wider rows.

How many rows can I print before running out of letters?

Total letters printed for n rows is n(n+1)/2. With A-Z (26 letters), the largest n that fits is 6 (21 letters). For 7 rows you would need 28 letters, which exceeds A-Z unless you add wrap logic.

Sequential Alphabet Triangle in PHP

Beginner

⏱️ 6 min read

📚 Updated: Aug 2025

🎯 2 Code Examples

Nested loops

Sequential alphabet triangle A, B C, D E F through K L M N O in PHP

What You'll Learn

Each row is wider than the last, and letters stay in order across the whole triangle: A, then B C, then D E F, up to K L M N O for 5 rows.

Unlike patterns that reset letters per row, this one uses a single counter that keeps advancing.

⭐ Pattern Output

For rows = 5 (letters separated by spaces):

Output

A
B C
D E F
G H I J
K L M N O

Complete PHP Program

Fixed rows = 5 version:

PHP

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

$k = 0;

for ($i = 0; $i < $rows; $i++) {
    for ($j = 0; $j <= $i; $j++) {
        echo $alpha[$k++] . ($j === $i ? '' : ' ');
    }
    echo PHP_EOL;
}

🧠 How It Works

Alphabet array + counter

$alpha holds A..Z and $k is the next index to print.

Outer loop controls row width

Row $i prints $i+1 letters.

Inner loop prints and advances

$k++ runs once per printed letter, so the alphabet continues across rows.

Print the line break

After building one row, print PHP_EOL to move to the next line. This keeps the output readable in CLI output.

Newline

Put it together

The outer loop controls rows, the inner loops control what prints on each row, and PHP_EOL separates the lines.

Variation — User Input (CLI) Version

Reads rows from standard input and clamps to a safe max (6) to stay within A–Z:

PHP

<?php
echo "Enter the number of rows (max 6): ";
$rows = (int) trim(fgets(STDIN));
$rows = max(1, min($rows, 6));

$alpha = range('A', 'Z');
$k = 0;

for ($i = 0; $i < $rows; $i++) {
    for ($j = 0; $j <= $i; $j++) {
        echo $alpha[$k++] . ($j === $i ? '' : ' ');
    }
    echo PHP_EOL;
}

💡 Tips for Enhancement

Try These

Remove spaces by echoing only the letter
Switch to lowercase using range('a','z')
Add wrap logic (mod 26) if you want more rows

Avoid

Resetting $k inside the outer loop (you will repeat A at every row)
Letting $k exceed 25 without wrap logic

❓ Frequently Asked Questions

Why use range('A', 'Z')?

It creates an array of uppercase letters so you can print alphabets using simple numeric indexes (0 for A, 1 for B, ...).

Why do we print PHP_EOL instead of <br>?

PHP_EOL is correct for CLI output and keeps examples consistent for terminal execution. In HTML, you would use <br> instead.

What is the time complexity of these pattern programs?

Most pattern programs print O(n) characters per row for n rows, so they are typically O(n²).

Next: PHP Alphabet Pattern 14

Continue to the next program for another alphabet pattern in PHP.

Program 14 →

About the author

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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