Number-Star Diamond Pattern in PHP

Beginner
⏱️ 7 min read
📚 Updated: Aug 2025
🎯 2 Code Examples
Modulo
Number-star diamond pattern output in PHP (1, 2*2, 3*3*3, ..., 1)

What You’ll Learn

How to print a number-star diamond pattern in PHP that grows from 1 to 5 and then shrinks back to 1:

1, 2*2, 3*3*3, ..., 1.

We use two sections: an increasing part (1..n) and a decreasing part (n-1..1).

⭐ Pattern Output

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

Output
1
2*2
3*3*3
4*4*4*4
5*5*5*5*5
4*4*4*4
3*3*3
2*2
1
1

Complete PHP Program

We print 2*$i - 1 characters per row. Odd positions print the number, even positions print *.

PHP
<?php
$n = 5;

for ($i = 1; $i <= $n; $i++) {
    for ($j = 1; $j < $i * 2; $j++) {
        echo ($j % 2 === 0) ? "*" : $i;
    }
    echo PHP_EOL;
}

for ($i = $n - 1; $i >= 1; $i--) {
    for ($j = 1; $j < $i * 2; $j++) {
        echo ($j % 2 === 0) ? "*" : $i;
    }
    echo PHP_EOL;
}

🧠 How It Works

1

Set n

$n = 5; sets the peak row number.

Setup
2

Build the top half

The first outer loop prints rows from 1 up to $n.

Growing
3

Alternate number and *

The inner loop runs 2*$i - 1 times. Even positions print *, odd positions print the number.

Alternation
4

Build the bottom half

The second outer loop prints rows from $n-1 back down to 1, forming the diamond shape.

Shrinking
=

Number-star diamond

Row lengths increase by 2 until the peak, then decrease by 2.

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 < $i * 2; $j++) {
        echo ($j % 2 === 0) ? "*" : $i;
    }
    echo PHP_EOL;
}

for ($i = $n - 1; $i >= 1; $i--) {
    for ($j = 1; $j < $i * 2; $j++) {
        echo ($j % 2 === 0) ? "*" : $i;
    }
    echo PHP_EOL;
}

💡 Tips for Enhancement

Try These

  • Replace * with another separator like - or |
  • Center-align the pattern by adding leading spaces on each row
  • Print spaces around * for readability: echo " * "
  • Use this alternation technique for binary and checkerboard patterns
  • Increase n to create a taller diamond

Avoid

  • Using $j <= $i*2 (that would add an extra character per row)
  • Forgetting the bottom-half loop (you’ll get only the top triangle)
  • Skipping input validation in CLI mode
  • Assuming alignment without adding spaces/padding

Key Takeaways

1

Each row prints 2*i - 1 characters.

2

Odd positions print the row number; even positions print *.

3

Two outer loops form the diamond: increasing then decreasing.

4

The same technique generalizes to many alternating-symbol patterns.

❓ Frequently Asked Questions

Because the inner loop runs while $j < $i * 2, which means it runs for 1..(2*i-1).
Yes—print a space instead of *, but keep in mind the row won’t look separated unless you add other formatting.
Print leading spaces before the inner loop. The number of spaces should decrease as i increases, and then increase again in the second half.
O(n²) for n rows.

Explore More PHP Number Patterns!

Once you master alternation with modulo, you can create many mixed symbol/number designs.

All Number Patterns →
Did you know?

Alternating output by parity (odd/even) is a common trick in patterns, grids, and even UI zebra-striping.

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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