Reverse Descending Number Triangle in PHP

Beginner
⏱️ 5 min read
📚 Updated: Aug 2025
🎯 2 Code Examples
Nested Loops
Reverse descending number triangle output (54321, 4321, 321, 21, 1) in PHP programming

What You’ll Learn

How to print a reverse descending number triangle in PHP using nested for loops. Each row starts from the current row limit and counts down to 1.

This pattern strengthens your understanding of descending loops and how the inner loop length depends on the outer loop value.

⭐ Pattern Output

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

Output
54321
4321
321
21
1
1

Complete PHP Program

Fixed $n = 5 version:

PHP
<?php
$n = 5;

for ($i = $n; $i >= 1; $i--) {
    for ($j = $i; $j >= 1; $j--) {
        echo $j;
    }
    echo PHP_EOL;
}

🧠 How It Works

1

Choose the size

$n = 5; sets the triangle height and the largest digit printed.

Setup
2

Outer loop (descending rows)

for ($i = $n; $i >= 1; $i--) controls how many digits appear on each row by decreasing the row limit.

Row control
3

Inner loop (print $i..1)

for ($j = $i; $j >= 1; $j--) prints digits from the row limit down to 1 using echo $j;.

Number printing
4

New line

echo PHP_EOL; ends the row and moves to the next line.

Line break
=

Reverse descending triangle

Total printed digits are still triangular: 1+2+…+n = n(n+1)/2, so the time complexity is O(n²).

2

Variation — User Input (CLI) Version

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

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

for ($i = $n; $i >= 1; $i--) {
    for ($j = $i; $j >= 1; $j--) {
        echo $j;
    }
    echo PHP_EOL;
}

💡 Tips for Enhancement

Try These

  • Validate input (reject $n < 1) before printing
  • Add spaces between numbers (for example, echo $j . " ";)
  • Print the increasing version by counting $j up from 1 to $i (Program 1)
  • Right-align the triangle by printing leading spaces
  • Try printing the same idea with letters to build alphabet patterns

Avoid

  • Forgetting the newline after each row
  • Using negative or zero values without validating input
  • Mixing up loop directions (use -- for descending loops)
  • Assuming CLI input is always valid (guard fgets() and casting if needed)

Key Takeaways

1

The outer loop decreases the row length by counting down from $n to 1.

2

The inner loop prints from $i down to 1 on each row.

3

Total printed digits still follow a triangular count: n(n+1)/2.

4

This pattern is a good stepping stone for inverted pyramids and mirrored patterns.

❓ Frequently Asked Questions

Because the inner loop starts at $j = $i and decrements until 1, printing $i, $i-1, ... , 1 on the same line.
Set $n to the size you want. For example, $n = 7 prints 7654321, then 654321, down to 1.
Yes—use echo $j . " "; instead of echo $j;.
O(n²) for n rows: total prints are 1+2+…+n = n(n+1)/2.

Next: PHP Number Pattern 4

Continue to Program 4 to learn another number pattern using nested loops in PHP.

Program 4 →
Did you know?

Descending loops are common in pattern problems because they naturally shrink the number of printed digits row by row—perfect for inverted shapes.

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)

12 people found this page helpful

PHP Number Pattern 2 PHP Number Pattern 4