Question

I have installed the .NET Framework 4.5 but I can only use .NET Framework 4.0 in my project, which doesn’t support BigInteger. Do I need Visual Studio 2012 for 4.5 or is Visual Studio 2010 fine for 4.5?

Answer 1

As others have noted, BigInteger was introduced in .NET 4.0, not .NET 4.5. Through our exchange in the comments, it appears that you had not referenced System.Numerics.dll in your project.

VS project references tell the C# compiler which assemblies define the types that will be used in the C# code being compiled. The default Visual Studio project templates do not include references to the entire .NET framework. Several more specialized assemblies, such as System.Numerics, are omitted; if you want to use them, you have to add the reference yourself.

People frequently confuse the using directive (using System.Numerics;) with the reference itself. The using directive only helps the compiler with resolving type names; it concerns a namespace. For the compiler to find the types themselves, you need a reference, which identifies an assembly.

That information should help clarify the error message “The type or namespace name ‘Numerics’ does not exist in the namespace ‘System’ (are you missing an assembly reference?)”. This means that the compiler has examined all the referenced assemblies, and it has found no type or namespace called System.Numerics.

To add an assembly reference in VS 2010:

1. Open the solution explorer
2. Expand the node for the project in question
3. Right-click the References node
4. Choose “Add Reference…”. A dialogue box opens.
5. Open the “.NET” tab
6. Locate “System.Numerics” in the Component Name list
7. Click the “OK” button.