title: Mono.Math.BigInteger is inaccessible due to its protection level
body: <p>So I'm working on a program in C# using ideone and I'm working with Mono for the first time. I'm trying to use the BigInteger class (Mono.Math.BigInteger) but I keep getting errors. Here's me code below. What is going on and how do I fix it? Thanks.    </p>
  
  <pre><code>using System;
  using Mono.Math;
  
  public class TFIB
  {       
      public static int Main()
      {       
          const int FIB_SEQUENCE_SIZE = 300;
          BigInteger[] FibonacciSequence = new BigInteger[FIB_SEQUENCE_SIZE];
  
          // Calculate Fibonacci Sequence
          FibonacciSequence[0] = 0;
          FibonacciSequence[1] = 1;
  
          for (int i = 2; i &lt; FIB_SEQUENCE_SIZE; i++)
          {
              FibonacciSequence[i] = FibonacciSequence[i - 1] + FibonacciSequence[i - 2];
          }
  
          while (true)
          {
              string[] tokenInput = Console.ReadLine().Split(' ');
              Mono.Math.BigInteger lowerBound = Mono.Math.BigInteger.Parse(tokenInput[0]);
              BigInteger upperBound = BigInteger.Parse(tokenInput[1]);
              if (lowerBound == 0 &amp;&amp; upperBound == 0)
              {
                  break;  // ending sequence found
              }
              else
              {
                  // find the number of fibonacci sequences
                  int numbersInRange = 0;
  
                  for (int i = 0; i &lt; FIB_SEQUENCE_SIZE; i++)
                  {
                      if (FibonacciSequence[i] &gt;= lowerBound)
                      {
                          if (FibonacciSequence[i] &lt;= upperBound)
                          {
                              numbersInRange++;
                          }
                          else
                          {
                              continue;   // there is nothing more to find
                          }
                      }
                  }
  
                  Console.WriteLine(numbersInRange);
              }
          }
  
          return 0;
      }
  }
  </code></pre>
  
  <p>These are the errors I'm getting:</p>
  
  <p>prog.cs(9,13): error CS0122: <code>Mono.Math.BigInteger' is inaccessible due to its protection level
  /usr/lib/mono/2.0/mscorlib.dll (Location of the symbol related to previous error)
  prog.cs(9,23): error CS0122:</code>Mono.Math.BigInteger[]' is inaccessible due to its protection level
  /usr/lib/mono/2.0/mscorlib.dll (Location of the symbol related to previous error)
  prog.cs(23,27): error CS0122: <code>Mono.Math.BigInteger' is inaccessible due to its protection level
  /usr/lib/mono/2.0/mscorlib.dll (Location of the symbol related to previous error)
  prog.cs(24,17): error CS0122:</code>Mono.Math.BigInteger' is inaccessible due to its protection level
  /usr/lib/mono/2.0/mscorlib.dll (Location of the symbol related to previous error)
  Compilation failed: 4 error(s), 0 warnings</p>