Shrinking Repeating Number Pattern in C++

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 C++ 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 C++ 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.

cout vs newline

Same line / next line

Repeated digits use cout << i; end each row with cout << "\n".

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 C++ 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 cout << i, then cout << "\n" 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

cout << i in the inner loop; cout << "\n" after.

Series Foundation

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

In short: for each row i from 1 to rows, repeat cout << i for j from i to rows, then call cout << "\n".

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.

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

Inputs & Outputs

ItemTypeDescription
rowsintNumber of triangle lines to print (typically ≥ 1).
Printed outputtextEach 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

ApproachIdeaBest for
Nested loopsOuter digit + inner repeatsLearning and interviews
string(rows - i + 1, char('0' + i))Build the full repeated row in one callCompact C++ style once loops are understood
Cheat Sheet

⚡ Quick Reference

GoalPattern
Walk each rowfor (i = 1; i <= rows; i++)
Repeat digit ifor (j = i; j <= rows; j++) cout << i;
End the rowcout << "\n";
One-line row shortcutstring(rows - i + 1, char('0' + i)) repeated per row
Program 11 variantfor (j = 1; j <= i; j++) cout << i (inverted triangle)
Compare

📋 cout vs newline vs string shortcut

Same pattern — different ways to emit characters.

cout << i
same line

Prints a digit without moving to the next line

cout << "\n"
new line

Ends the current row after all digits are printed

string row
whole row

Builds digit i repeated rows - i + 1 times in one string

Learning tip
loops first

Master nested loops before the string shortcut

Context

When This Pattern Shows Up

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

  1. First lab exercise

    Most C++ pattern series start here before pyramids and diamonds.

  2. Nested-loop warm-up

    Outer/inner bound practice with an immediate visual check.

  3. Stream I/O practice

    Combine loops with cin for a flexible row count.

  4. Gateway to variants

    Compare Program 9 (1, 22, 333, …) and Program 11 (55555, 4444, …) next.

  5. 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.

Try 5, 7, or 10. Larger values still work up to 20.

Live result
Press "Draw pattern".
Hands-On

Examples Gallery

Three complete C++ programs — fixed row count, cin input, and a string row 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.

C++
#include <iostream>
using namespace std;

int main() {
    int rows = 5;
    int i, j;

    for (i = 1; i <= rows; ++i) {
        for (j = i; j <= rows; ++j) {
            cout << i;
        }
        cout << "\n";
    }

    return 0;
}

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. cout << "\n" 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 cin >> rows (check cin.fail() in real apps).

C++
#include <iostream>
using namespace std;

int main() {
    int rows;
    int i, j;

    cout << "Enter the number of rows: ";
    cin >> rows;

    for (i = 1; i <= rows; ++i) {
        for (j = i; j <= rows; ++j) {
            cout << i;
        }
        cout << "\n";
    }

    return 0;
}

How It Works

Same nested-loop core as Example 1; only the source of rows changes. Non-numeric input sets cin’s fail bit if you ignore errors — always validate in safer labs.

⚡ Shortcut Style

Same shape using a string constructor instead of an inner repeat loop.

Example 3 — string(rows - i + 1, char('0' + i))

Build each row with string(rows - i + 1, char('0' + i)), then print with cout.

C++
#include <iostream>
#include <string>
using namespace std;

int main() {
    int rows = 5;

    for (int i = 1; i <= rows; ++i) {
        cout << string(rows - i + 1, char('0' + i)) << "\n";
    }

    return 0;
}

How It Works

string(rows - i + 1, char('0' + i)) creates a row of digit i repeated exactly rows - i + 1 times when i is 1..9. Same shape as Example 1 without an inner repeat loop — a handy C++ shortcut once the bounds make sense.

🧠 How the Algorithm Prints Rows

1

Set up

#include <iostream> brings in cout / cin. Set rows (fixed or from input).

Setup
2

Outer loop (rows)

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

Row
3

Inner loop (repeats)

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

Repeats
4

New line

cout << "\n" 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.

iInner j rangeRepeatsPrinted row
11..441111
22..43222
33..4233
44..414

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. Stream Formatting Drills

Practice cout vs row newline without complex math.

Example: put cout << "\n" inside the inner loop by mistake.

4. Character Substitution

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

Example: print 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 cin 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. 1. Instant Visual Feedback

    Wrong bounds show up immediately as a broken staircase.

  2. 2. Minimal Concepts

    Only loops and console output — no arrays or math libraries.

  3. 3. Easy to Extend

    Invert, center, hollow, or change the fill character with small edits.

  4. 4. O(1) Extra Memory

    Streaming output needs no storage beyond loop counters.

Pro Tip: learn the nested-loop version first; treat string(rows - i + 1, char('0' + i)) as a polish shortcut afterward.

Usage Tips

Small habits that keep number-pattern code clean.

  1. 1. Name Bounds Clearly

    Use rows (or n) and keep i/j for row/column — or rename to row/col.

  2. 2. Prefer cin

    Avoid crashes when the user types letters instead of a number.

  3. 3. Keep cout << "\n" Outside

    Only call cout << "\n" after the inner loop finishes the row.

  4. 4. Start at i, Not 1

    for (j = i; j <= rows; j++) with cout << i is the key to shrinking width.

  5. 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 cout << "\n" inside the inner loop.

Common Pitfalls

Mistakes that commonly break shrinking repeating number patterns.

  1. 1. cout << "\n" Inside the Inner Loop

    Each repeated digit lands on its own line — you get a column, not a triangle.

    → Use cout << i for repeats; cout << "\n" only after the inner loop.

  2. 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. 3. Forgetting the Row Break

    Omitting cout << "\n" glues every repeat onto one endless line.

    → Always end the row after the inner loop.

  4. 4. Unchecked cin

    Letters or empty input leave rows unset if you ignore cin errors.

    → Check cin.fail() after cin >> rows and re-prompt on failure.

  5. 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 cin input

Unchecked cin leaves rows unset — check cin.fail().

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

  • Use cin until rows >= 1
  • Then draw the pattern

4. Spaced output

  • Use cout << 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.
  • cout << i stays on the line; cout << "\n" advances — use both deliberately.
  • 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

ProgramTimeExtra space
Nested loops (Examples 1–2)O(rows²)O(1)
string(rows - i + 1, char('0' + i)) (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 string(rows - i + 1, char('0' + i)).

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 cout << i for each copy and cout << "\n" 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 cout << i for repeats and cout << "\n" after each row
  • Validate rows ≥ 1 for interactive programs
  • Check cin.fail() before using rows
  • State O(n²) time when asked about complexity

❌ Don’t

  • Call cout << "\n" 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.

5
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

cout << "\n"

Ends each row

I/O
O 05

Complexity

O(n²) time

Analysis
🎯 You’re ready to print a shrinking repeating number pattern in C++
Review Quick Reference →

❓ Frequently Asked Questions

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.
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.
cout << i stays on the same line. cout << "\n" ends the current line. Repeated digits use cout << i; the row break uses cout << "\n" after the inner loop.
Use the inner loop as 1..i instead of i..rows so the repeat count grows (see Program 9).
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).
O(n²) where n is the number of rows. Total cout digit outputs equal n+(n-1)+…+1 = n(n+1)/2.
Yes. cout << string(rows - i + 1, char('0' + i)) << "\n" prints a full row in one call. Nested loops are better for learning; the string constructor is a handy shortcut later.
After cin >> rows, check cin.fail() or use if (!(cin >> rows)) to handle bad input. Unchecked cin leaves rows unset on failure.
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
Mari Selvan M P 🔗

Developer, cloud engineer, and technical writer

  • Experience 12 years building web and cloud systems
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