Shrinking Repeating Number Pattern in PHP

Q: What is the time complexity?

O(n²) where n is the number of rows. Total echo calls equal n+(n-1)+…+1 = n(n+1)/2.

Q: Can I use str_repeat instead of an inner loop?

Yes. echo str_repeat((string)$i, $rows - $i + 1) . PHP_EOL prints a full row in one call. Nested loops are better for learning; str_repeat is a handy shortcut once the bounds make sense.

Q: How should I read the row count safely?

Use trim(fgets(STDIN)) and check is_numeric($input) before casting to int so bad input does not produce unexpected results.

Q: What happens if rows is 0 or negative?

The outer loop never runs, so nothing is printed. Validate and prompt again if you want a clear user message.

Beginner

⏱️ 8 min read

📚 Updated: Aug 2026

🎯 3 Code Examples

🚀 Live Preview

Nested Loops

Shrinking repeating number pattern output (11111, 2222, 333, 44, 5) in PHP programming

Overview

What You’ll Learn

The shrinking repeating number pattern teaches how a changing inner-loop start value controls row width. This tutorial covers the shape rule, loop structure, a live preview, algorithm steps, worked PHP examples, edge cases, and complexity.

Shape Rule

digit i repeats rows − i + 1 times

Row 1 prints 11111, row 2 prints 2222, and so on until the last row prints a single digit.

Outer Loop

Rows

for ($i = 1; $i <= $rows; $i++) walks each line as the digit increases from 1 to $rows.

Inner Loop

Digits

for ($j = $i; $j <= $rows; $j++) prints digit $i exactly $rows − $i + 1 times on that row.

echo vs PHP_EOL

Same line / next line

Repeated digits use echo $i; end each row with echo PHP_EOL;.

Live Preview

1–20 rows

Pick a row count and draw the shrinking repeating number pattern instantly in the browser.

O(n²)

Complexity

Total digit prints still = n(n+1)/2; extra memory stays O(1).

Introduction

A shrinking repeating number pattern repeats the row digit on each line, but the row becomes shorter as i increases. With rows = 5, the output is 11111, 2222, 333, 44, 5.

In PHP you solve it with two nested for loops: the outer loop picks the digit, the inner loop runs from $i to $rows and repeats it with echo $i;, then echo PHP_EOL; moves to the next line.

Why it matters?

It is a great follow-up after growing and inverted repeating patterns. Once you see how the inner-loop start controls width, many number triangles become predictable.

Key Highlights

Row = Repeat Count

On row i, print digit i exactly rows − i + 1 times.

Two Nested Loops

Outer picks the digit; inner controls how many times it repeats.

Print Then Break

echo $i in the inner loop; echo PHP_EOL; after.

Series Foundation

Compare Program 9 (growing repeats) and Program 11 (inverted triangle).

In short: for each row i from 1 to rows, repeat echo $i for j from i to rows, then call echo PHP_EOL;.

Foundation

📝 Problem & Approach

Given a positive integer rows, print a shrinking repeating number pattern: row i repeats digit i exactly rows − i + 1 times, with the outer loop counting from 1 up to rows.

PHP

// First 5 rows (conceptual shape)
// 11111
// 2222
// 333
// 44
// 5

Inputs & Outputs

Item	Type	Description
`rows`	int	Number of triangle lines to print (typically ≥ 1).
Printed output	text	Each row repeats one digit; row `i` has `rows − i + 1` copies of `i`, so the first row is widest.

Minimal workflow

Pseudocode

for i from 1 to rows:
    for j from i to rows:
        print i (no newline)
    print newline

Approach comparison

Approach	Idea	Best for
Nested loops	Outer digit + inner repeats	Learning and interviews
`str_repeat((string) $i, $rows - $i + 1)` in inner loop	Print a full repeated row with `str_repeat`	Leaner C style once loops are understood

Cheat Sheet

⚡ Quick Reference

Goal	Pattern
Walk each row	`for ($i = 1; $i <= $rows; $i++)`
Repeat digit `i`	`for ($j = $i; $j <= $rows; $j++) echo $i;`
End the row	`echo PHP_EOL;`
One-line row shortcut	`str_repeat((string) $i, $rows - $i + 1)` repeated per row
Program 11 variant	`for ($j = 1; $j <= $i; $j++) echo $i;` (Program 9 ascending repeats)

Compare

📋 echo vs str_repeat vs PHP_EOL

Same pattern — different ways to emit characters.

echo $i

same line

Prints a digit without moving to the next line

echo PHP_EOL;

new line

Ends the current row after all digits are printed

str_repeat((string) $i, $rows - $i + 1)

one digit

Writes digit i when i is 1..9 — no format string

Learning tip

loops first

Master nested loops before the str_repeat shortcut

Context

When This Pattern Shows Up

Reach for this pattern when teaching how inner-loop bounds control row width.

First lab exercise
Most PHP pattern series start here before pyramids and diamonds.
Nested-loop warm-up
Outer/inner bound practice with an immediate visual check.
Console I/O practice
Combine loops with fgets(STDIN) for a flexible row count.
Gateway to variants
Compare Program 9 (1, 22, 333, …) and Program 11 (55555, 4444, …) next.
Not a UI layout tool
This is a console teaching pattern — not how you build modern app screens.

Key benefit: one small program that locks in nested loops, output sequencing, and O(n²) thinking.

Interactive

🔮 Live Preview

Choose a row count between 1 and 20 and draw the shrinking repeating number pattern in the browser.

Hands-On

Examples Gallery

Three complete PHP programs — fixed row count, CLI input, and a str_repeat shortcut. Click View Output to reveal sample console results.

📚 Getting Started

Print five rows of the shrinking repeating number pattern with nested loops.

Example 1 — Fixed `rows = 5`

Hard-coded height — outer picks digit, inner runs from i to rows.

PHP

<?php
$rows = 5;

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

How It Works

When i = 1, the inner loop runs from 1 to 5 and prints 11111. When i = 2, it prints 2222, and so on until i = rows prints a single 5. echo PHP_EOL; after the inner loop starts the next row.

📈 Practical Variant

Let the user choose the height at runtime.

Example 2 — User Input Version

Read the row count with (int) trim(fgets(STDIN)) (check is_numeric() in real apps).

PHP

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

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

How It Works

Same nested-loop core as Example 1; only the source of rows changes. Non-numeric input casts to 0 without validation — check is_numeric(trim($line)) in safer labs.

⚡ Shortcut Style

Same shape without an explicit inner repeat loop.

Example 3 — `str_repeat((string) $i, $rows - $i + 1)`

Build each row with str_repeat((string) $i, $rows - $i + 1), then end with echo PHP_EOL;.

PHP

<?php
$rows = 5;

for ($i = 1; $i <= $rows; $i++) {
    echo str_repeat((string) $i, $rows - $i + 1) . PHP_EOL;
}

How It Works

str_repeat((string) $i, $rows - $i + 1) creates a string of repeated digit i. Great once you understand the nested-loop idea; keep the two-loop version for exams that ask you to show both bounds.

🧠 How the Algorithm Prints Rows

Set up

Set $rows = 5; and use fgets(STDIN) when reading input from the terminal.

Setup

Outer loop (rows)

for ($i = 1; $i <= $rows; $i++) picks the digit; the inner loop prints it $rows - $i + 1 times.

Row

Inner loop (repeats)

for ($j = $i; $j <= $rows; $j++) repeats digit $i with echo $i; as the row shrinks.

Repeats

New line

echo PHP_EOL; ends the row so the next outer iteration starts fresh.

Break

Pattern complete

Total digit prints: 1+2+…+n = n(n+1)/2 — O(n²) time, O(1) extra memory.

Trace

🔎 Worked Walkthrough — `rows = 4`

Trace each outer-loop value of i and count how many times the inner loop prints digit i.

`i`	Inner `j` range	Repeats	Printed row
`1`	`1..4`	4	`1111`
`2`	`2..4`	3	`222`
`3`	`3..4`	2	`33`
`4`	`4..4`	1	`4`

Total digit prints: 1 + 2 + 3 + 4 = 10 = 4×5/2.

Use Cases

Where this tiny pattern (and its loop structure) shows up beyond the homework prompt.

1. Teaching Nested Loops

Clearest visual proof that outer and inner bounds interact.

Example: change j <= i and watch the shape change.

2. Pattern Series Base

Foundation for inverted, pyramid, diamond, and hollow variants.

Example: change inner bound to j <= i for growing repeats (Program 9).

3. Console Formatting Drills

Practice echo vs PHP_EOL without complex math.

Example: put echo PHP_EOL; inside the inner loop by mistake.

4. Character Substitution

Swap digits for letters, stars, or spaced output once the loop works.

Example: use echo $i . " "; for spaced repeated digits on each row.

5. Complexity Intuition

Triangular totals make O(n²) concrete for beginners.

Example: count printed digits for n = 10 still → 55.

6. Input Validation Labs

Pair the pattern with fgets(STDIN) and positive-row checks.

Example: reject rows <= 0 and re-prompt.

Pro Tip: when an interviewer asks for patterns, explain the outer/inner roles first — then write the loops. The story matters as much as the code.

Advantages

Why this pattern earns a permanent spot in beginner C courses.

1. Instant Visual Feedback
Wrong bounds show up immediately as a broken staircase.
2. Minimal Concepts
Only loops and console output — no arrays or math libraries.
3. Easy to Extend
Invert, center, hollow, or change the fill character with small edits.
4. O(1) Extra Memory
Streaming output needs no storage beyond loop counters.

Pro Tip: learn the nested-loop version first; treat str_repeat((string) $i, $rows - $i + 1) as a polish shortcut afterward.

Usage Tips

Small habits that keep number-pattern code clean.

1. Name Bounds Clearly
Use rows (or n) and keep i/j for row/column — or rename to row/col.
2. Validate CLI input
Avoid crashes when the user types letters instead of a number.
3. Keep echo PHP_EOL; Outside
Only call echo PHP_EOL; after the inner loop finishes the row.
4. Start at i, Not 1
for ($j = $i; $j <= $rows; $j++) with echo $i; is the key to shrinking width.
5. Dry-Run One Small n
Trace rows = 3 on paper before coding larger demos.

Pro Tip: if the output is a vertical list of single digits per line, you almost certainly put echo PHP_EOL; inside the inner loop.

Common Pitfalls

Mistakes that commonly break shrinking repeating number patterns.

1. echo PHP_EOL; Inside the Inner Loop
Each repeated digit lands on its own line — you get a column, not a triangle.
→ Use echo $i for repeats; echo PHP_EOL; only after the inner loop.
2. Wrong Inner Bound
j <= i grows repeats; j = 1 with wrong bound prints a rectangle.
→ For this shape, keep for ($j = $i; $j <= $rows; $j++).
3. Forgetting the Row Break
Omitting echo PHP_EOL; glues every repeat onto one endless line.
→ Always end the row after the inner loop.
4. Unchecked CLI input
Letters or empty input throw undefined rows.
→ Check is_numeric(trim($line)) and re-prompt on failure.
5. Off-by-One on 0-Based Loops
Switching to i = 0 without adjusting the inner bound prints an empty first row or wrong counts.
→ If 0-based, print i with wrong inner bound (e.g. j <= i + 1).

Edge Cases

Check these inputs before calling the solution done.

rows = 1

Single digit

Output is just 1 on one line.

rows = 0

Empty pattern

Outer loop never runs — print nothing or show a message.

Negative

`rows < 0`

Treat as invalid; re-prompt instead of silent empty output.

Large n

Many rows

Output grows as n²/2 characters — fine for labs, noisy for huge n.

Bad input

Non-numeric CLI input

Unchecked CLI leaves rows unset — call is_numeric(trim($line)) first.

Fill char

Inner bound j = 1 by mistake

Use j = i so row width shrinks as i grows.

Drill

🎯 Practice Problems

Try these variations to lock in the pattern.

1. Growing repeating pattern

Inner loop j from 1 to i (see Program 9)
Prints 1, 22, 333, …

2. Inverted repeating triangle

Outer loop from rows down to 1
Continue with Program 11

3. Safe input loop

Check is_numeric() until $rows >= 1
Then draw the pattern

4. Spaced output

Use echo $i between repeated digits
Harder follow-up after this page

Important

Notes

Triangular count. Total digit prints for n rows is n(n+1)/2 — hence O(n²) time.
echo $i; stays on the line; echo PHP_EOL; advances — mix them carefully.
Validate rows > 0 for interactive programs; rows = 1 should print a single 1.
This page is left-aligned. Centered pyramids need leading spaces — covered later in the series.

Quick Takeaway: outer loop picks the digit, inner loop runs from i to rows, then break the line — that is the whole pattern.

Analysis

⏱️ Time and Space Complexity

Program	Time	Extra space
Nested loops (Examples 1–2)	`O(rows²)`	`O(1)`
`str_repeat((string) $i, $rows - $i + 1)` (Example 3)	`O(rows²)`	`O(rows)` per row string (temporary)

Wrap Up

🎉 Conclusion

The shrinking repeating number pattern is a compact nested-loop exercise: digit increases each row while repeat count shrinks. Master the classic two-loop version, then optionally shorten rows with str_repeat((string) $i, $rows - $i + 1).

Practice the three examples above, then continue to Program 13 for the alternating zigzag number triangle.

Row i repeats digit i exactly rows - i + 1 times — keep echo $i for each copy and echo PHP_EOL; for the break.

View Examples Gallery Continue to Program 13

Pro Tips

💡 Best Practices

✅ Do

Explain outer picks digit, inner start at i before coding
Use echo $i for repeats and echo PHP_EOL; after each row
Validate rows ≥ 1 for interactive programs
Check is_numeric() before using $rows
State O(n²) time when asked about complexity

❌ Don’t

Call echo PHP_EOL; inside the inner repeat loop
Use j = 1 when you meant Program 9 instead
Skip the newline after each row
Ignore bad console input in user-facing demos
Skip the rows = 1 edge case

Summary

Key Takeaways

Knowledge Unlocked

Five things to remember about this shrinking pattern

Print the pattern the beginner-friendly way.

Core concepts

△ 01

Rule

Row i repeats digit i (rows-i+1) times

Definition

↻ 02

Outer loop

Picks the digit each row

Code

1 03

Inner loop

Runs from i to rows

Code

↵ 04

echo PHP_EOL;

Ends each row

I/O

O 05

Complexity

O(n²) time

Analysis

❓ Frequently Asked Questions

Why does the row length shrink each time?

The inner loop runs from j = i to rows. As i increases (1, 2, 3, …), the inner loop runs fewer times, so each row prints fewer copies of the row digit.

Why does the first row have five 1s?

On the first row, i = 1 and the inner loop runs from 1 to rows, so it prints 1 exactly rows times — five 1s when rows = 5.

What is the difference between echo and PHP_EOL?

echo stays on the same line. echo PHP_EOL ends the current line. Repeated digits use echo $i; the row break uses echo PHP_EOL after the inner loop.

How do I print 1, 22, 333, … instead?

Use the inner loop as 1..i instead of i..rows so the repeat count grows (see Program 9).

How is this different from Program 11?

Program 11 counts the outer loop down and repeats digit i exactly i times (55555, 4444, 333, 22, 1). Program 12 counts up and uses for ($j = $i; $j <= $rows; $j++) so digit i repeats rows - i + 1 times (11111, 2222, 333, 44, 5).

What is the time complexity?

O(n²) where n is the number of rows. Total echo calls equal n+(n-1)+…+1 = n(n+1)/2.

Can I use str_repeat instead of an inner loop?

Yes. echo str_repeat((string)$i, $rows - $i + 1) . PHP_EOL prints a full row in one call. Nested loops are better for learning; str_repeat is a handy shortcut once the bounds make sense.

How should I read the row count safely?

Use trim(fgets(STDIN)) and check is_numeric($input) before casting to int so bad input does not produce unexpected results.

What happens if rows is 0 or negative?

The outer loop never runs, so nothing is printed. Validate and prompt again if you want a clear user message.

Did you Know? 🔊

Row digit i repeats rows − i + 1 times. The outer loop counts up from 1, while the inner loop runs from i to rows, so each row shrinks — still O(n²) total prints.

Continue to Program 13

Next up — alternating ascending/descending rows in Program 13.

Program 13 tutorial →

About the author

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 11 — Inverted Repeating Number Triangle PHP Number Pattern 13 — Alternating Rows

Shrinking Repeating Number Pattern in PHP

What You’ll Learn

Shape Rule

Outer Loop

Inner Loop

echo vs PHP_EOL

Live Preview

O(n²)

Introduction

Why it matters?

Row = Repeat Count

Two Nested Loops

Print Then Break

Series Foundation

📝 Problem & Approach

Inputs & Outputs

Minimal workflow

Approach comparison

⚡ Quick Reference

📋 echo vs str_repeat vs PHP_EOL

When This Pattern Shows Up

First lab exercise

Nested-loop warm-up

Console I/O practice

Gateway to variants

Not a UI layout tool

🔮 Live Preview

Examples Gallery

📚 Getting Started

Example 1 — Fixed rows = 5

How It Works

📈 Practical Variant

Example 2 — User Input Version

How It Works

⚡ Shortcut Style

Example 3 — str_repeat((string) $i, $rows - $i + 1)

How It Works

🧠 How the Algorithm Prints Rows

Set up

Outer loop (rows)

Inner loop (repeats)

New line

Pattern complete

🔎 Worked Walkthrough — rows = 4

Use Cases

1. Teaching Nested Loops

2. Pattern Series Base

3. Console Formatting Drills

4. Character Substitution

5. Complexity Intuition

6. Input Validation Labs

Advantages

1. Instant Visual Feedback

2. Minimal Concepts

3. Easy to Extend

4. O(1) Extra Memory

Usage Tips

1. Name Bounds Clearly

2. Validate CLI input

3. Keep echo PHP_EOL; Outside

4. Start at i, Not 1

5. Dry-Run One Small n

Common Pitfalls

1. echo PHP_EOL; Inside the Inner Loop

2. Wrong Inner Bound

3. Forgetting the Row Break

4. Unchecked CLI input

5. Off-by-One on 0-Based Loops

Edge Cases

Single digit

Empty pattern

rows < 0

Many rows

Non-numeric CLI input

Inner bound j = 1 by mistake

🎯 Practice Problems

1. Growing repeating pattern

2. Inverted repeating triangle

3. Safe input loop

4. Spaced output

Example 1 — Fixed `rows = 5`

Example 3 — `str_repeat((string) $i, $rows - $i + 1)`

🔎 Worked Walkthrough — `rows = 4`

`rows < 0`