Hollow Diamond Inside Square Star Pattern in PHP

Beginner
⏱️ 10 min read
📚 Updated: Aug 2025
🎯 2 Code Examples
2n wide, 2n − 1 tall
Hollow diamond inside square frame star pattern in PHP programming

What You'll Learn

You print a frame with a solid row of * on the first line and again on the last line, and mirror the rows in between so the middle row is narrowest (only the left and right border stars with a wide hollow gap).

The width is 2 * rows; the number of lines is 2 * rows - 1. This layout differs from the standalone hollow diamond outline (Program 9).

⭐ Pattern Output

When you run the program with rows = 5:

Output
**********
****  ****
***    ***
**      **
*        *
**      **
***    ***
****  ****
**********
1

Complete PHP Program

Fixed rows = 5 version:

PHP
<?php
$rows = 5;
$height = 2 * $rows - 1;
$width = 2 * $rows;

for ($line = 1; $line <= $height; $line++) {
    if ($line == 1 || $line == $height) {
        for ($j = 1; $j <= $width; $j++) echo "*";
    } else {
        $i = ($line <= $rows) ? $line : (2 * $rows - $line);
        $left = $rows - $i + 1;
        $gap = 2 * ($i - 1);

        for ($j = 1; $j <= $left; $j++) echo "*";
        for ($j = 1; $j <= $gap; $j++) echo " ";
        for ($j = 1; $j <= $left; $j++) echo "*";
    }
    echo PHP_EOL;
}

🧠 How It Works

1

Grid size

$height = 2 * $rows - 1; is the number of lines. $width = 2 * $rows; is the number of characters per full bar row. The shape is wider than the standalone hollow diamond (Program 9) because the frame uses an even width.

Grid
2

Top and bottom frame rows

for ($line = 1; $line <= $height; $line++) visits every line. When $line == 1 or $line == $height, for ($j = 1; $j <= $width; $j++) echo "*"; prints a solid horizontal edge.

Frame
3

Middle rows: mirror index, left stars, gap, right stars

Otherwise compute $i = ($line <= $rows) ? $line : (2 * $rows - $line); so rows equidistant from the top and bottom share the same pattern. Then $left = $rows - $i + 1; and $gap = 2 * ($i - 1);. Print $left stars, $gap spaces, then $left stars again—the hollow diamond cavity between the two vertical star runs.

Interior
4

Finish the line

Every branch ends with echo PHP_EOL;. O(n²) output for n = $rows, O(1) extra space. Lines of length 2 * $rows scroll horizontally in the green preview on phones.

Line break
=

Diamond in a frame

Solid top and bottom bars cap a hollow diamond carved from paired star columns. Matches $rows = 5 sample output (first lines shown).

2

Variation — User Input (CLI) Version

Read rows from standard input (works when you run the file from terminal using php):

PHP
<?php
echo "Enter the number of rows: ";
$rows = (int) trim(fgets(STDIN));

$height = 2 * $rows - 1;
$width = 2 * $rows;

for ($line = 1; $line <= $height; $line++) {
    if ($line == 1 || $line == $height) {
        for ($j = 1; $j <= $width; $j++) echo "*";
    } else {
        $i = ($line <= $rows) ? $line : (2 * $rows - $line);
        $left = $rows - $i + 1;
        $gap = 2 * ($i - 1);

        for ($j = 1; $j <= $left; $j++) echo "*";
        for ($j = 1; $j <= $gap; $j++) echo " ";
        for ($j = 1; $j <= $left; $j++) echo "*";
    }
    echo PHP_EOL;
}

💡 Tips for Enhancement

Try These

  • Validate $rows > 0 before printing
  • Print only the hollow diamond outline (Program 9) for comparison
  • Change the frame character (e.g., use #)
  • Use str_repeat() to build each line as a string
  • Try making the frame hollow (border only) instead of solid top/bottom bars

Avoid

  • Using 2 * $rows - 1 as width (this pattern uses 2 * $rows)
  • Forgetting to mirror $i for the bottom half
  • Mixing tabs and spaces (alignment breaks)
  • Forgetting newline after each line
  • Assuming user input is always valid

Key Takeaways

1

Width is 2 * $rows and height is 2 * $rows - 1.

2

Top and bottom lines are fully filled with stars (frame).

3

Middle lines are symmetric using mirrored $i values.

4

Time complexity is O(n²) for n rows.

5

This is a different layout than the standalone hollow diamond (Program 9).

❓ Frequently Asked Questions

This classic layout uses width 2 * $rows and height 2 * $rows - 1 so the top and bottom can be solid horizontal bars while the inner rows close on the left and right sides.
Program 9 prints only the diamond outline with constant width 2 * $rows - 1. Program 11 adds a frame-like look using width 2 * $rows and solid top/bottom rows.
It’s O(n²) because there are Theta(n) lines and each prints Theta(n) characters.

Explore: All Star Patterns

Browse the full PHP star pattern series.

All Patterns →
Did you know?

This pattern is a popular variation because it combines a frame-like look with a symmetric hollow diamond.

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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