Ascending Number Triangle in C#

Beginner
⏱️ 5 min read
📚 Updated: Aug 2025
🎯 2 Code Examples
Nested Loops
Ascending number triangle output (1, 12, 123, 1234, 12345) in C# programming

What You’ll Learn

How to print an ascending number triangle in C# using nested for loops. Each row starts at 1 and prints up to the current row index: 1, 12, 123, and so on.

This pattern is a simple way to understand how the outer loop controls the number of rows and the inner loop controls how many digits appear on each row.

⭐ Pattern Output

For rows = 5, the pattern looks like this:

Output
1
12
123
1234
12345
1

Complete C# Program

The outer loop counts from 1 to rows. The inner loop prints numbers from 1 to the current row index.

C#
using System;

namespace MyApp
{
    class Program
    {
        static void Main(string[] args)
        {
            int rows = 5;
            int i, j;

            for (i = 1; i <= rows; i++)
            {
                for (j = 1; j <= i; j++)
                {
                    Console.Write(j);
                }
                Console.WriteLine();
            }
        }
    }
}

🧠 How It Works

1

Set the number of rows

int rows = 5; sets the height of the triangle.

Setup
2

Outer loop (row control)

for (i = 1; i <= rows; i++) decides which row you are printing.

Row control
3

Inner loop (print 1..i)

for (j = 1; j <= i; j++) prints the digits for the current row.

Number printing
4

New line

Console.WriteLine() moves to the next row after printing each line.

Line break
=

Ascending number triangle

Total prints are 1+2+…+n = n(n+1)/2, so time complexity is O(n²) for n rows.

2

Variation — User Input Version

Let the user choose the number of rows at runtime:

C#
using System;

namespace MyApp
{
    class Program
    {
        static void Main(string[] args)
        {
            Console.Write("Enter the number of rows: ");
            int rows = Convert.ToInt32(Console.ReadLine());

            for (int i = 1; i <= rows; i++)
            {
                for (int j = 1; j <= i; j++)
                {
                    Console.Write(j);
                }
                Console.WriteLine();
            }
        }
    }
}

💡 Tips for Enhancement

Try These

  • Validate input with int.TryParse before converting
  • Add spacing with Console.Write(j + " ")
  • Right-align the triangle by printing leading spaces before each row
  • Print the row number repeatedly to create repeating-number patterns

Avoid

  • Forgetting Console.WriteLine() after each row
  • Using Convert.ToInt32 without handling invalid input
  • Putting the newline inside the inner loop (breaks the row)

Key Takeaways

1

The outer loop runs rows from 1 to rows.

2

The inner loop prints from 1 to the current row index i.

3

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

4

The same loop idea helps build pyramids, Floyd’s triangle, and many other patterns.

❓ Frequently Asked Questions

Because the first time through the outer loop, i = 1, so the inner loop prints j from 1 to 1.
Count the outer loop down from rows to 1: for (i = rows; i >= 1; i--). Keep the inner loop printing 1..i.
O(n²) for n rows since total prints are n(n+1)/2.

Explore More C# Number Patterns!

Try inversions, alignments, and repeating digits to level up your nested-loop skills.

All Number Patterns →
Did you know?

The total number of printed digits grows like a triangular number. If you print n rows, the total count is 1+2+…+n = 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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