Right-Aligned Descending Number Triangle in PHP

Beginner
⏱️ 6 min read
📚 Updated: Aug 2025
🎯 2 Code Examples
Alignment
Right-aligned descending number triangle output in PHP (1, 21, 321, 4321, 54321)

What You’ll Learn

How to print a right-aligned descending number triangle in PHP:

1, 21, 321, 4321, 54321.

The alignment comes from printing spaces first and numbers only when the column index is within the current row width.

⭐ Pattern Output

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

Output
    1
   21
  321
 4321
54321
1

Complete PHP Program

We count down from $n to 1. If $j > $i, we print spaces; otherwise we print $j.

PHP
<?php
$n = 5;

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

🧠 How It Works

1

Set n

$n = 5; sets the width and the number of rows.

Setup
2

Outer loop (row size)

$i increases from 1 to n, so each row prints one more digit than the previous.

Rows
3

Inner loop (descending columns)

The inner loop counts down from $n to 1, which naturally yields the row digits in descending order.

Columns
4

Spaces vs digits

When $j > $i we print spaces; when $j <= $i we print the digit $j.

Alignment
=

Right-aligned triangle

Indentation shrinks each row, so the triangle stays aligned to the right edge.

2

Variation — User Input (CLI) Version

Let the user decide the value of $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 = $n; $j >= 1; $j--) {
        echo ($j > $i) ? "  " : $j;
    }
    echo PHP_EOL;
}

💡 Tips for Enhancement

Try These

  • Center-align the triangle by printing leading spaces based on row width
  • Add spaces between digits and adjust indentation accordingly
  • Print the ascending version by looping j from 1..i
  • Use printf padding for multi-digit alignment when n is large
  • Replace digits with characters to generate symbol triangles

Avoid

  • Using inconsistent indentation widths (it breaks the alignment)
  • Forgetting the newline after each row
  • Mixing row/column logic in nested loops
  • Skipping input validation in CLI mode

Key Takeaways

1

The inner loop counts down from $n to 1 to print descending digits.

2

Spaces are printed when the column index is outside the current row.

3

As the row grows, indentation shrinks, creating right alignment.

4

Generalize easily by changing n or reading it from input.

❓ Frequently Asked Questions

Those positions are outside the triangle for the current row, so spaces keep the numbers aligned to the right.
Skip printing spaces and print only when $j <= $i.
Yes—use an inner loop from $j = $i down to 1 and print directly without leading spaces.
O(n²) for n rows.

Explore More PHP Number Patterns!

Right-aligned patterns help you understand spacing logic—use it to build pyramids and diamonds next.

All Number Patterns →
Did you know?

Alignment in patterns is often just counting spaces. Once you control whitespace, you can design nearly any triangle, pyramid, or 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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