BigInteger Class in C#

The BigInteger class in C# is designed to handle arbitrarily large integers that exceed the limits of standard integer types. It is part of the System.Numerics namespace and provides support for mathematical operations on very large numbers without overflow.

Unlike built-in integer types like int or long, BigInteger can represent integers of any size, limited only by available memory. This makes it ideal for cryptographic calculations, mathematical computations, and scenarios requiring precise arithmetic with large numbers.

Syntax

The BigInteger structure declaration −

[SerializableAttribute]
public struct BigInteger : IFormattable, IComparable, IComparable<BigInteger>, IEquatable<BigInteger>

Creating a BigInteger instance −

BigInteger num = new BigInteger(value);
BigInteger num = BigInteger.Parse("12345678901234567890");

BigInteger Constructors

Creating BigInteger Instances

Example

using System;
using System.Numerics;

class Program {
   public static void Main() {
      // Creating BigInteger from different data types
      BigInteger num1 = new BigInteger(123456789);
      BigInteger num2 = new BigInteger(double.MaxValue);
      BigInteger num3 = BigInteger.Parse("98765432109876543210");
      
      Console.WriteLine("From int: " + num1);
      Console.WriteLine("From double.MaxValue: " + num2);
      Console.WriteLine("From string: " + num3);
      
      // Creating very large number using multiplication
      BigInteger largeNum = BigInteger.Multiply(Int64.MaxValue, Int64.MaxValue);
      Console.WriteLine("Large number: " + largeNum);
   }
}

The output of the above code is −

From int: 123456789
From double.MaxValue: 179769313486231570814527423731704356798070567525844996598917476803157260780028538760589558632766878171540458953514382464234321326889464182768467546703537516986049910576551282076245490090389328944075868508455133942304583236903222948165808559332123348274797826204144723168738177180919299881250404026184124858368
From string: 98765432109876543210
Large number: 85070591730234615847396907784232501249

BigInteger Operations

Example

using System;
using System.Numerics;

class Program {
   public static void Main() {
      BigInteger a = BigInteger.Parse("123456789012345678901234567890");
      BigInteger b = BigInteger.Parse("987654321098765432109876543210");
      
      // Arithmetic operations
      Console.WriteLine("Addition: " + BigInteger.Add(a, b));
      Console.WriteLine("Subtraction: " + BigInteger.Subtract(b, a));
      Console.WriteLine("Multiplication: " + BigInteger.Multiply(a, 2));
      Console.WriteLine("Division: " + BigInteger.Divide(b, 10));
      
      // Power operation
      BigInteger power = BigInteger.Pow(2, 100);
      Console.WriteLine("2^100: " + power);
   }
}

The output of the above code is −

Addition: 1111111110111111111011111111100
Subtraction: 864197532086419753208641975320
Multiplication: 246913578024691357802469135780
Division: 98765432109876543210987654321
2^100: 1267650600228229401496703205376

BigInteger vs Standard Integer Types

Conclusion

The BigInteger class in C# provides unlimited precision integer arithmetic, making it essential for applications requiring calculations with very large numbers. While it offers flexibility and prevents overflow, it comes with performance trade-offs compared to standard integer types, so use it when precision with large numbers is more important than speed.