C# Online Compiler | .NET Fiddle

using System;
using System.Diagnostics;
using System.Collections.Generic;

public class Program {
	public static void Main() {
		Random r = new Random();
		for (int i = 0; i < 10000; i++) {
			var rndBase = r.Next(2, 62);
			var encoded = NumberToBase(i, rndBase);
			var decoded = NumberFromBase(encoded, rndBase);
			if (i != decoded) {
				Console.WriteLine("i: {0} enc: {1} dec: {2}", i, encoded, decoded);
			}
		}
		Console.WriteLine("Completed no errors");
	}

	// Define other methods and classes here
	private const string BASE_DIGITS = "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz";
	/// <summary>
	/// Convert a base 10 number to a different base.
	/// </summary>
	/// <param name = "number">Number to convert</param>
	/// <param name = "toBase">Base to use</param>
	/// <returns>String</returns>
	public static string NumberToBase(long number, int toBase) {
		Debug.Assert(toBase >= 2 && toBase <= BASE_DIGITS.Length);
		if (number == 0) return "0";
		if (number < 0) throw new ArgumentOutOfRangeException("number", number, "Number cannot be negative");
		
		var baseChars = BASE_DIGITS.ToCharArray();
		var result = new Stack<char>();
		while (number != 0) {
			result.Push(baseChars[number % toBase]);
			number /= toBase;
		}

		return new string (result.ToArray());
	}

	/// <summary>
	/// Convert a string in a different base to a base 10 number
	/// </summary>
	/// <param name = "number">Number to convert</param>
	/// <param name = "fromBase">Base to convert from</param>
	/// <returns>Int64</returns>
	public static long NumberFromBase(string number, int fromBase) {
		Debug.Assert(fromBase >= 2 && fromBase <= BASE_DIGITS.Length);
		long result = 0;
		long multiplier = 1;
		for (var i = number.Length - 1; i >= 0; i--) {
			result += BASE_DIGITS.IndexOf(number[i]) * multiplier;
			multiplier *= fromBase;
		}

		return result;
	}
}

 
using System;
using System.Diagnostics;
using System.Collections.Generic;
​
public class Program {
    public static void Main() {
        Random r = new Random();
        for (int i = 0; i < 10000; i++) {
            var rndBase = r.Next(2, 62);
            var encoded = NumberToBase(i, rndBase);
            var decoded = NumberFromBase(encoded, rndBase);
            if (i != decoded) {
                Console.WriteLine("i: {0} enc: {1} dec: {2}", i, encoded, decoded);
            }
        }
        Console.WriteLine("Completed no errors");
    }
​
    // Define other methods and classes here
    private const string BASE_DIGITS = "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz";
    /// <summary>
    /// Convert a base 10 number to a different base.
    /// </summary>
    /// <param name = "number">Number to convert</param>