Alternating Binary Number Triangle (Starting with 1) in C#

Beginner
⏱️ 5 min read
📚 Updated: Aug 2025
🎯 2 Code Examples
Modulo Operator
Alternating binary number triangle output (1, 10, 101, 1010, 10101) in C# programming

What You’ll Learn

How to print an alternating binary number triangle in C# where each row starts with 1 and alternates: 1, 10, 101, 1010, 10101.

The trick is printing j % 2 while j counts from 1 upward on each row.

⭐ Pattern Output

For rows = 5, the pattern looks like this:

Output
1
10
101
1010
10101
1

Complete C# Program

The outer loop controls the number of rows. The inner loop prints j % 2 from j = 1 to j = i.

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 % 2);
                }
                Console.WriteLine();
            }
        }
    }
}

🧠 How It Works

1

Set the size

rows decides how many lines to print.

Setup
2

Outer loop (row length grows)

i increases from 1 to rows, so each row prints one extra digit.

Row control
3

Inner loop (print j%2)

As j goes 1, 2, 3, ... the expression j % 2 prints 1, 0, 1, 0, ...

Modulo
=

Alternating binary pattern

Total prints are triangular: n(n+1)/2, so time complexity is O(n²).

2

Variation — Start with 0

If you want rows to start with 0 instead of 1, flip the output:

C#
using System;

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

            for (int i = 1; i <= rows; i++)
            {
                for (int j = 1; j <= i; j++)
                {
                    Console.Write(1 - (j % 2));
                }
                Console.WriteLine();
            }
        }
    }
}

💡 Tips for Enhancement

Try These

  • Read rows from the console to scale the pattern
  • Alternate by row+column with (i + j) % 2
  • Add spaces between digits for readability

Avoid

  • Forgetting the newline after each row
  • Using string concatenation inside the loops

Key Takeaways

1

j % 2 alternates between 1 and 0 as j increments.

2

The outer loop controls how many digits each row prints.

3

This pattern is a quick exercise for modulo + nested loops.

4

Overall complexity is \(O(n^2)\) for \(n\) rows.

❓ Frequently Asked Questions

Because j runs 1 then 2 and j % 2 prints 1 then 0.
Yes. You can toggle a variable between 0 and 1 on each print, but modulo is the simplest for this pattern.
O(n²) for n rows since total prints are n(n+1)/2.

Explore More C# Number Patterns!

Try switching the loop direction or using row+column parity to create even more binary patterns.

All Number Patterns →
Did you know?

Alternating 0/1 patterns are closely related to parity checks, checkerboards, and XOR logic.

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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