Symmetric Number Mirror Pattern in PHP

Beginner
⏱️ 7 min read
📚 Updated: Aug 2025
🎯 2 Code Examples
Spacing & Loops
Symmetric number mirror output in PHP (1 1, 12 21, 123 321, 1234 4321, 1234554321)

What You’ll Learn

How to print a symmetric number mirror pattern in PHP, where the left side grows as 1..i and the right side mirrors as i..1.

Example final row: 1234554321.

This pattern is a good practice for nested loops plus carefully controlled spacing.

⭐ Pattern Output

For $n = 5, the pattern looks like this:

Output
1        1
12      21
123    321
1234  4321
1234554321
1

Complete PHP Program

We print the left numbers, then spaces, then the right mirrored numbers, using conditions based on the current row $i.

PHP
<?php
$n = 5;

for ($i = 1; $i <= $n; $i++) {
    for ($j = 1; $j <= $n; $j++) {
        if ($j <= $i) {
            echo $j;
        } else {
            echo "  ";
        }
    }

    for ($k = $n; $k >= 1; $k--) {
        if ($k > $i) {
            echo " ";
        } else {
            echo $k;
        }
    }

    echo PHP_EOL;
}

🧠 How It Works

1

Set n

$n = 5; controls the maximum digit and number of rows.

Setup
2

Left side: print 1..i

The first inner loop prints digits when $j <= $i; otherwise it prints spaces.

Left half
3

Right side: mirror i..1

The second inner loop counts down from $n to 1 and prints digits only when $k <= $i.

Right half
=

Symmetric mirror

As $i increases, the middle gap shrinks until both halves touch.

2

Variation — User Input (CLI) Version

Let the user choose $n at runtime (run from terminal with php):

PHP
<?php
echo "Enter n (e.g., 5): ";
$n = (int) trim(fgets(STDIN));

if ($n < 1) {
    echo "Please enter a positive number." . PHP_EOL;
    exit(1);
}

for ($i = 1; $i <= $n; $i++) {
    for ($j = 1; $j <= $n; $j++) {
        echo ($j <= $i) ? $j : "  ";
    }
    for ($k = $n; $k >= 1; $k--) {
        echo ($k > $i) ? " " : $k;
    }
    echo PHP_EOL;
}

💡 Tips for Enhancement

Try These

  • Use printf padding to align multi-digit values when n is large
  • Replace spaces with dots while debugging alignment
  • Center-align the whole output by adding leading spaces per row
  • Build each row as an array and join for precise spacing control
  • Make a full diamond by adding a second half where i decreases

Avoid

  • Mixing different space widths between loops (it breaks symmetry)
  • Forgetting the newline after each row
  • Assuming single-digit numbers when n becomes large
  • Skipping validation in the CLI version

Key Takeaways

1

Left half prints 1..i; right half mirrors as i..1.

2

Middle spacing shrinks as the row grows.

3

Nested loops + simple conditions are enough to build symmetry.

4

For bigger n, use formatting/padding to keep alignment readable.

❓ Frequently Asked Questions

Because the right side is printed in reverse order and only up to the current row index, mirroring the left side.
Reduce the number of spaces printed when $j > $i and when $k > $i. Keeping both sides consistent preserves symmetry.
Yes—print $j . " " and $k . " " instead of concatenating digits with no spaces.
O(n²) for n rows, since each row performs two loops of length n.

Explore More PHP Number Patterns!

Spacing-based mirror patterns are excellent practice for alignment and loop control.

All Number Patterns →
Did you know?

Many console/terminal patterns become easier if you build each row as a string first, then print it once—especially when alignment matters.

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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