Repeating-Letter Alphabet Triangle in PHP
What You'll Learn
Row 1 prints one A, row 2 prints two Bs, row 3 prints three Cs, and so on: A, BB, CCC, DDDD, EEEEE.
This is a great beginner exercise to practice loop boundaries and understand how the outer loop chooses the row’s letter.
⭐ Pattern Output
For rows = 5:
A
BB
CCC
DDDD
EEEEEComplete PHP Program
Fixed rows = 5 version (nested loops):
<?php
$rows = 5;
$alpha = range('A', 'Z');
for ($i = 0; $i < $rows; $i++) {
for ($j = 0; $j <= $i; $j++) {
echo $alpha[$i];
}
echo PHP_EOL;
}🧠 How It Works
Build the alphabet array
$alpha = range('A','Z'); gives letters A..Z by index (0 is A, 1 is B, ...).
Outer loop chooses the row letter
When $i is 0, the row uses $alpha[0] (A). When $i is 1, the row uses B, and so on.
Inner loop controls how many repeats
The inner loop runs $i + 1 times, so the current row letter repeats 1, 2, 3, 4, 5 times.
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.
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 max of 26:
<?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 = 0; $i < $rows; $i++) {
for ($j = 0; $j <= $i; $j++) {
echo $alpha[$i];
}
echo PHP_EOL;
}💡 Tips for Enhancement
Try These
- Replace the inner loop with
str_repeat($alpha[$i], $i + 1) - Switch to lowercase using
range('a', 'z') - Center-align the triangle by printing leading spaces
- Compare with Program 1 (letters change inside the row)
Avoid
- Updating the letter inside the inner loop unless you want mixed letters per row
- Allowing
$rows> 26 without handling the alphabet size - Using
<br>in CLI examples (usePHP_EOL)
Key Takeaways
The outer loop selects the row’s letter: A, then B, then C, ...
The inner loop repeats that letter i+1 times.
Total characters printed is \(n(n+1)/2\), so runtime is O(n²).
❓ Frequently Asked Questions
$alpha[$i] repeatedly for a row. To print AB, ABC, etc., you would print $alpha[$j] inside the inner loop (see Program 1).$alpha[$i] . ' ' inside the inner loop, or join with spacing using str_repeat plus a separator strategy.Next: PHP Alphabet Pattern 10
Continue to the next program for another alphabet pattern in PHP.
You can compute the row letter without an array: chr(ord('A') + $i). Using range() is often easier to read for beginners.
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