How can I do this elegantly with C# and .NET 3.5/4?
For example, a number can be between 1 and 100.
I know a simple if would suffice; but the keyword to this question is elegance. It's for my toy project not for production.
This questions wasn't about speed, but about code beauty. Stop talking about efficiency and such; remember you're preaching to the choir.
There are a lot of options:
int x = 30;
if (Enumerable.Range(1,100).Contains(x))
//true
if (x >= 1 && x <= 100)
//true
Also, check out this SO post for regex options.