Incrementing Start Number Triangle in PHP

Beginner
⏱️ 5 min read
📚 Updated: Aug 2025
🎯 2 Code Examples
Nested Loops
Incrementing start number triangle output (12345, 2345, 345, 45, 5) in PHP programming

What You’ll Learn

How to print an incrementing start number triangle in PHP using nested for loops. Each row starts from the row number and continues up to $n.

This pattern helps you practice writing an inner loop whose start value depends on the outer loop variable.

⭐ Pattern Output

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

Output
12345
2345
345
45
5
1

Complete PHP Program

Fixed $n = 5 version:

PHP
<?php
$n = 5;

for ($i = 1; $i <= $n; $i++) {
    for ($j = $i; $j <= $n; $j++) {
        echo $j;
    }
    echo PHP_EOL;
}

🧠 How It Works

1

Choose the size

$n = 5; sets the last number printed on each row.

Setup
2

Outer loop (row index)

for ($i = 1; $i <= $n; $i++) controls which row you are printing (and what number the row starts with).

Row control
3

Inner loop (print $i..$n)

for ($j = $i; $j <= $n; $j++) prints digits starting from the current row start $i up to $n using echo $j;.

Number printing
4

New line

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

Line break
=

Incrementing start triangle

Total numbers printed is still 1+2+…+n = n(n+1)/2, so the time complexity is O(n²) for n rows.

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 = 1; $i <= $n; $i++) {
    for ($j = $i; $j <= $n; $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 $j . " ";)
  • Print the descending-start version by counting the outer loop down and printing 1..$i
  • Right-align the rows by printing leading spaces before each row
  • Use the same loop idea to generate alphabet or star patterns

Avoid

  • Forgetting the newline after each row
  • Using negative or zero values without validating input
  • Mixing row/column logic (outer loop = rows)
  • Assuming CLI input is always valid (guard fgets() and casting if needed)

Key Takeaways

1

The outer loop controls the row number (and thus the starting digit).

2

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

3

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

4

The same technique works for star patterns and alphabet patterns.

❓ Frequently Asked Questions

Because the inner loop starts at $j = $i. As $i increases each row, the first printed digit becomes 1, 2, 3, 4, ...
Set $n to the size you want. For example $n = 7 will print rows starting at 1..7, then 2..7, down to 7.
Yes—use echo $j . " "; instead of echo $j;. You may also want to trim() the row if you build it as a string.
O(n²) for n rows: total prints are 1+2+…+n = n(n+1)/2.

Next: PHP Number Pattern 3

Continue to Program 3 to practice another number pattern using nested loops in PHP.

Program 3 →
Did you know?

Even though the rows look different, the amount of work is still triangular: you print n + (n-1) + ... + 1 digits, which is n(n+1)/2.

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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