What reusable code should every developer have in their toolbox? [closed]

Question

I'm trying to build up a library of reusable code to use from project to project. As I write code snippets and components, I'm trying to decide which libraries I will get the most use out of long term VS will I really use this again?

What code or components do you reuse that should every developer have?

I'm primarily interested in .net web and winforms.

Answer 1

Regular Expressions for verifying

• Valid Date
• Valid Number
• Between two Dates
• Zip
• Postal
• Age
• Number Range

Depending on the language as some have these features already