Using .Net, how can I determine if a type is a Numeric ValueType?

But here's an example:

Dim desiredType as Type
if IsNumeric(desiredType) then ...

EDIT: I only know the Type, not the Value as a string.

Ok, so unfortunately I have to cycle through the TypeCode.

But this is a nice way to do it:

 if ((desiredType.IsArray))
      return 0;

 switch (Type.GetTypeCode(desiredType))
 {
      case 3:
      case 6:
      case 7:
      case 9:
      case 11:
      case 13:
      case 14:
      case 15:
          return 1;
 }
 ;return 0;

A few years late here, but here's my solution (you can choose whether to include boolean). Solves for the Nullable case. XUnit test included

/// <summary>
/// Determines if a type is numeric.  Nullable numeric types are considered numeric.
/// </summary>
/// <remarks>
/// Boolean is not considered numeric.
/// </remarks>
public static bool IsNumericType( Type type )
{
    if (type == null)
    {
        return false;
    }

    switch (Type.GetTypeCode(type))
    {
        case TypeCode.Byte:
        case TypeCode.Decimal:
        case TypeCode.Double:
        case TypeCode.Int16:
        case TypeCode.Int32:
        case TypeCode.Int64:
        case TypeCode.SByte:
        case TypeCode.Single:
        case TypeCode.UInt16:
        case TypeCode.UInt32:
        case TypeCode.UInt64:
            return true;
        case TypeCode.Object:
            if ( type.IsGenericType && type.GetGenericTypeDefinition() == typeof(Nullable<>))
            {
               return IsNumericType(Nullable.GetUnderlyingType(type));
            }
            return false;
    }
    return false;
}



/// <summary>
/// Tests the IsNumericType method.
/// </summary>
[Fact]
public void IsNumericTypeTest()
{
    // Non-numeric types
    Assert.False(TypeHelper.IsNumericType(null));
    Assert.False(TypeHelper.IsNumericType(typeof(object)));
    Assert.False(TypeHelper.IsNumericType(typeof(DBNull)));
    Assert.False(TypeHelper.IsNumericType(typeof(bool)));
    Assert.False(TypeHelper.IsNumericType(typeof(char)));
    Assert.False(TypeHelper.IsNumericType(typeof(DateTime)));
    Assert.False(TypeHelper.IsNumericType(typeof(string)));

    // Arrays of numeric and non-numeric types
    Assert.False(TypeHelper.IsNumericType(typeof(object[])));
    Assert.False(TypeHelper.IsNumericType(typeof(DBNull[])));
    Assert.False(TypeHelper.IsNumericType(typeof(bool[])));
    Assert.False(TypeHelper.IsNumericType(typeof(char[])));
    Assert.False(TypeHelper.IsNumericType(typeof(DateTime[])));
    Assert.False(TypeHelper.IsNumericType(typeof(string[])));
    Assert.False(TypeHelper.IsNumericType(typeof(byte[])));
    Assert.False(TypeHelper.IsNumericType(typeof(decimal[])));
    Assert.False(TypeHelper.IsNumericType(typeof(double[])));
    Assert.False(TypeHelper.IsNumericType(typeof(short[])));
    Assert.False(TypeHelper.IsNumericType(typeof(int[])));
    Assert.False(TypeHelper.IsNumericType(typeof(long[])));
    Assert.False(TypeHelper.IsNumericType(typeof(sbyte[])));
    Assert.False(TypeHelper.IsNumericType(typeof(float[])));
    Assert.False(TypeHelper.IsNumericType(typeof(ushort[])));
    Assert.False(TypeHelper.IsNumericType(typeof(uint[])));
    Assert.False(TypeHelper.IsNumericType(typeof(ulong[])));

    // numeric types
    Assert.True(TypeHelper.IsNumericType(typeof(byte)));
    Assert.True(TypeHelper.IsNumericType(typeof(decimal)));
    Assert.True(TypeHelper.IsNumericType(typeof(double)));
    Assert.True(TypeHelper.IsNumericType(typeof(short)));
    Assert.True(TypeHelper.IsNumericType(typeof(int)));
    Assert.True(TypeHelper.IsNumericType(typeof(long)));
    Assert.True(TypeHelper.IsNumericType(typeof(sbyte)));
    Assert.True(TypeHelper.IsNumericType(typeof(float)));
    Assert.True(TypeHelper.IsNumericType(typeof(ushort)));
    Assert.True(TypeHelper.IsNumericType(typeof(uint)));
    Assert.True(TypeHelper.IsNumericType(typeof(ulong)));

    // Nullable non-numeric types
    Assert.False(TypeHelper.IsNumericType(typeof(bool?)));
    Assert.False(TypeHelper.IsNumericType(typeof(char?)));
    Assert.False(TypeHelper.IsNumericType(typeof(DateTime?)));

    // Nullable numeric types
    Assert.True(TypeHelper.IsNumericType(typeof(byte?)));
    Assert.True(TypeHelper.IsNumericType(typeof(decimal?)));
    Assert.True(TypeHelper.IsNumericType(typeof(double?)));
    Assert.True(TypeHelper.IsNumericType(typeof(short?)));
    Assert.True(TypeHelper.IsNumericType(typeof(int?)));
    Assert.True(TypeHelper.IsNumericType(typeof(long?)));
    Assert.True(TypeHelper.IsNumericType(typeof(sbyte?)));
    Assert.True(TypeHelper.IsNumericType(typeof(float?)));
    Assert.True(TypeHelper.IsNumericType(typeof(ushort?)));
    Assert.True(TypeHelper.IsNumericType(typeof(uint?)));
    Assert.True(TypeHelper.IsNumericType(typeof(ulong?)));

    // Testing with GetType because of handling with non-numerics. See:
    // http://msdn.microsoft.com/en-us/library/ms366789.aspx

    // Using GetType - non-numeric
    Assert.False(TypeHelper.IsNumericType((new object()).GetType()));
    Assert.False(TypeHelper.IsNumericType(DBNull.Value.GetType()));
    Assert.False(TypeHelper.IsNumericType(true.GetType()));
    Assert.False(TypeHelper.IsNumericType('a'.GetType()));
    Assert.False(TypeHelper.IsNumericType((new DateTime(2009, 1, 1)).GetType()));
    Assert.False(TypeHelper.IsNumericType(string.Empty.GetType()));

    // Using GetType - numeric types
    // ReSharper disable RedundantCast
    Assert.True(TypeHelper.IsNumericType((new byte()).GetType()));
    Assert.True(TypeHelper.IsNumericType(43.2m.GetType()));
    Assert.True(TypeHelper.IsNumericType(43.2d.GetType()));
    Assert.True(TypeHelper.IsNumericType(((short)2).GetType()));
    Assert.True(TypeHelper.IsNumericType(((int)2).GetType()));
    Assert.True(TypeHelper.IsNumericType(((long)2).GetType()));
    Assert.True(TypeHelper.IsNumericType(((sbyte)2).GetType()));
    Assert.True(TypeHelper.IsNumericType(2f.GetType()));
    Assert.True(TypeHelper.IsNumericType(((ushort)2).GetType()));
    Assert.True(TypeHelper.IsNumericType(((uint)2).GetType()));
    Assert.True(TypeHelper.IsNumericType(((ulong)2).GetType()));
    // ReSharper restore RedundantCast

    // Using GetType - nullable non-numeric types
    bool? nullableBool = true;
    Assert.False(TypeHelper.IsNumericType(nullableBool.GetType()));
    char? nullableChar = ' ';
    Assert.False(TypeHelper.IsNumericType(nullableChar.GetType()));
    DateTime? nullableDateTime = new DateTime(2009, 1, 1);
    Assert.False(TypeHelper.IsNumericType(nullableDateTime.GetType()));

    // Using GetType - nullable numeric types
    byte? nullableByte = 12;
    Assert.True(TypeHelper.IsNumericType(nullableByte.GetType()));
    decimal? nullableDecimal = 12.2m;
    Assert.True(TypeHelper.IsNumericType(nullableDecimal.GetType()));
    double? nullableDouble = 12.32;
    Assert.True(TypeHelper.IsNumericType(nullableDouble.GetType()));
    short? nullableInt16 = 12;
    Assert.True(TypeHelper.IsNumericType(nullableInt16.GetType()));
    short? nullableInt32 = 12;
    Assert.True(TypeHelper.IsNumericType(nullableInt32.GetType()));
    short? nullableInt64 = 12;
    Assert.True(TypeHelper.IsNumericType(nullableInt64.GetType()));
    sbyte? nullableSByte = 12;
    Assert.True(TypeHelper.IsNumericType(nullableSByte.GetType()));
    float? nullableSingle = 3.2f;
    Assert.True(TypeHelper.IsNumericType(nullableSingle.GetType()));
    ushort? nullableUInt16 = 12;
    Assert.True(TypeHelper.IsNumericType(nullableUInt16.GetType()));
    ushort? nullableUInt32 = 12;
    Assert.True(TypeHelper.IsNumericType(nullableUInt32.GetType()));
    ushort? nullableUInt64 = 12;
    Assert.True(TypeHelper.IsNumericType(nullableUInt64.GetType()));
}

You can find out if a variable is numeric using the Type.GetTypeCode() method:

TypeCode typeCode = Type.GetTypeCode(desiredType);

if (typeCode == TypeCode.Double || typeCode == TypeCode.Integer || ...)
     return true;

You'll need to complete all the available numeric types in the "..." part ;)

More details here: TypeCode Enumeration

Great article here Exploring IsNumeric for C#.

Option 1:

Reference Microsoft.VisualBasic.dll, then do the following:

if (Microsoft.VisualBasic.Information.IsNumeric("5"))
{
 //Do Something
}

Option 2:

public static bool Isumeric (object Expression)
{
    bool f;
    ufloat64 a;
    long l;

    IConvertible iConvertible = null;
    if ( ((Expression is IConvertible)))
    {
       iConvertible = (IConvertible) Expression;
    }

    if (iConvertible == null)
{
   if ( ((Expression is char[])))
   {
       Expression = new String ((char[]) Expression);
       goto IL_002d; // hopefully inserted by optimizer
   }
   return 0;
}
IL_002d:
TypeCode typeCode = iConvertible.GetTypeCode ();
if ((typeCode == 18) || (typeCode == 4))
{
    string str = iConvertible.ToString (null);
   try
   {
        if ( (StringType.IsHexOrOctValue (str, l)))
   {
        f = true;
        return f;
   }
}
catch (Exception )
{
    f = false;
    return f;
};
return DoubleType.TryParse (str, a);
}
return Utils.IsNumericTypeCode (typeCode);
}

internal static bool IsNumericType (Type typ)
{
bool f;
TypeCode typeCode;
if ( (typ.IsArray))
{
    return 0;
}
switch (Type.GetTypeCode (typ))
{
case 3: 
case 6: 
case 7: 
case 9: 
case 11: 
case 13: 
case 14: 
case 15: 
   return 1;
};
return 0;
}

If you have a reference to an actual object, here's a simple solution for C# that's very straightforward:

    /// <summary>
    /// Determines whether the supplied object is a .NET numeric system type
    /// </summary>
    /// <param name="val">The object to test</param>
    /// <returns>true=Is numeric; false=Not numeric</returns>
    public static bool IsNumeric(ref object val)
    {
        if (val == null)
            return false;

        // Test for numeric type, returning true if match
        if 
            (
            val is double || val is float || val is int || val is long || val is decimal || 
            val is short || val is uint || val is ushort || val is ulong || val is byte || 
            val is sbyte
            )
            return true;

        // Not numeric
        return false;
    }