Concat strings by & and + in VB.Net

You've probably got Option Strict turned on (which is a good thing), and the compiler is telling you that you can't add a string and an int. Try this:

t = s1 & i.ToString()

& and + are both concatenation operators but when you specify an integer while using +, vb.net tries to cast "Hello" into integer to do an addition. If you change "Hello" with "123", you will get the result 124.

• & is only used for string concatenation.
• + is overloaded to do both string concatenation and arithmetic addition.

The double purpose of + leads to confusion, exactly like that in your question. Especially when Option Strict is Off, because the compiler will add implicit casts on your strings and integers to try to make sense of your code.

My recommendations

• You should definitely turn Option Strict On, then the compiler will force you to add explicit casts where it thinks they are necessary.
• You should avoid using + for concatenation because of the ambiguity with arithmetic addition.

Both these recommendations are also in the Microsoft Press book Practical Guidelines And Best Practises for VB and C# (sections 1.16, 21.2)