Ascending Number Triangle Pattern in PHP

What You’ll Learn

The ascending number triangle prints 1, 12, 123, 1234, 12345 — row $i concatenates digits 1 through $i. This tutorial covers nested-loop logic, live preview, worked PHP examples, edge cases, and O(n²) complexity.

📝 Problem & Approach

Given a positive integer $rows (e.g. 5), print an ascending number triangle: row $i prints digits 1 through $i with no spaces.

// $rows = 5 (conceptual shape)
// 1
// 12
// 123
// 1234
// 12345

Inputs & Outputs

Minimal workflow

for $i from 1 to $rows:
    for $j from 1 up to $i:
        echo $j
    newline

Approach comparison

🔮 Live Preview

Enter a row count and draw the ascending number triangle in the browser.

Press "Draw pattern".

Examples Gallery

Three complete PHP programs — fixed $rows = 5, fgets(STDIN) input, and a spaced-output variant. Click View Output to reveal sample console results.

<?php
$rows = 5;

for ($i = 1; $i <= $rows; $i++) {
    for ($j = 1; $j <= $i; $j++) {
        echo $j;
    }
    echo PHP_EOL;
}

1
12
123
1234
12345

<?php
echo "Enter the number of rows: ";
$input = trim(fgets(STDIN));
if (!is_numeric($input)) {
    echo "Invalid input." . PHP_EOL;
    exit(1);
}
$rows = (int) $input;

for ($i = 1; $i <= $rows; $i++) {
    for ($j = 1; $j <= $i; $j++) {
        echo $j;
    }
    echo PHP_EOL;
}

Enter the number of rows: 4
1
12
123
1234

<?php
$rows = 5;

for ($i = 1; $i <= $rows; $i++) {
    for ($j = 1; $j <= $i; $j++) {
        echo $j . " ";
    }
    echo PHP_EOL;
}

1
1 2
1 2 3
1 2 3 4
1 2 3 4 5

🔎 Worked Walkthrough — row $i = 3

Trace row 3 to see how the inner loop builds 123.

After the inner loop, echo PHP_EOL moves to the next row.

🎯 Practice Problems

Try these variations to lock in the pattern.

Notes

⏱️ Time and Space Complexity

💡 Best Practices