معادل توابع Mid و IsNumeric

[saghari]

با سلام
معادل توابع زیر (توی VB هستد) در C# چیه


Public Shared Function Mid( _
ByVal str As String, _
ByVal Start As Integer, _
Optional ByVal Length As Integer _
) As String


و
Public Function IsNumeric(ByVal Expression As Object) As Boolean

با تشکر

[mohammad diba]

سلام تابع mid


string a = "djskdjskds",b,c;
b=a.Substring(1, 4);
c = a.Substring(1);

[mohammad diba]

تابع isnumber


string a = "12"; bool b;
int k;
b = Int32.TryParse(1, out k);