Decreasing Length Sequential Number Pattern in C++

Beginner
⏱️ 6 min read
📚 Updated: Aug 2025
🎯 2 Code Examples
Formatting (setw)
Decreasing length sequential number pattern output (1..15) in C++ programming

What You’ll Learn

How to print a decreasing-length triangle of consecutive integers in C++.

The first row prints 5 numbers, the next prints 4, then 3, then 2, then 1—resulting in values from 1 to 15.

⭐ Pattern Output

For rows = 5, the pattern looks like this:

Output
  1  2  3  4  5
  6  7  8  9
 10 11 12
 13 14
 15
1

Complete C++ Program

A counter k prints consecutive numbers. The inner loop length shrinks each row.

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

int main() {
    int rows = 5;
    int i, j;
    int k = 1;

    for (i = 1; i <= rows; i++) {
        for (j = rows; j >= i; j--) {
            cout << setw(3) << k++;
        }
        cout << "\n";
    }

    return 0;
}

🧠 How It Works

1

Initialize the counter

k = 1 is the next number to print.

Setup
2

Outer loop controls rows

for (i = 1; i <= rows; i++) prints one line per iteration.

Row control
3

Inner loop shrinks each row

for (j = rows; j >= i; j--) runs rows - i + 1 times, so the row length decreases by 1 each line.

Length control
4

setw(3) formats output

setw(3) reserves 3 characters so values align as columns.

Formatting
=

Decreasing sequential triangle

Total printed numbers are n(n+1)/2, so work is O(n²) for n rows.

2

Variation — User Input Version

Let the user choose the number of rows using cin:

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

int main() {
    int rows;
    int i, j;
    int k = 1;

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

    for (i = 1; i <= rows; i++) {
        for (j = rows; j >= i; j--) {
            cout << setw(3) << k++;
        }
        cout << "\n";
    }

    return 0;
}

💡 Tips for Enhancement

Try These

  • Increase the setw() width for larger outputs (e.g., setw(4))
  • Start from a different initial number (set k to something else)
  • Print the increasing-length version by changing the inner loop bounds
  • Center-align the triangle by adding leading spaces per row
  • Replace numbers with characters to create alphabet triangles

Avoid

  • Forgetting to include <iomanip> when using setw()
  • Using endl inside loops (it flushes output and slows printing)
  • Hard-coding the row count everywhere (store it in one variable)
  • Reinitializing k inside the outer loop (that would restart numbering each row)

Key Takeaways

1

A counter k prints consecutive integers across all rows.

2

The inner loop length is rows - i + 1, so each row is shorter.

3

setw(3) ensures aligned columns for neat output.

4

Total printed numbers follow n(n+1)/2, so time is O(n²).

❓ Frequently Asked Questions

Because the inner loop condition is j >= i. When i increases, the loop runs one fewer time.
Yes. Move int k = 1; inside the outer loop. That will print 1..rowLength on every row instead of continuing the sequence.
Increase the field width: use setw(4) or more depending on the maximum value you plan to print.
O(n²) for n rows: total prints are 1+2+…+n.

Explore More C++ Number Patterns!

Try varying the inner loop bounds to create shrinking, growing, or centered number triangles.

All Number Patterns →
Did you know?

Patterns that count sequentially across rows often use a single counter like k. That one variable can turn many loop shapes into interesting number designs.

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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