Question

I could do this in C#..

int number = 2; string str = 'Hello ' + number + ' world'; 

..and str ends up as ‘Hello 2 world’.

In VB.NET i could do this..

Dim number As Integer = 2 Dim str As String = 'Hello ' + number + ' world' 

..but I get an InvalidCastException ‘Conversion from string ‘Hello ‘ to type ‘Double’ is not valid.’

I am aware that I should use .ToString() in both cases, but whats going on here with the code as it is?

Answer 1

In VB I believe the string concatenation operator is & rather than + so try this:

Dim number As Integer = 2 Dim str As String = 'Hello ' & number & ' world' 

Basically when VB sees + I suspect it tries do numeric addition or use the addition operator defined in a type (or no doubt other more complicated things, based on options…) Note that System.String doesn’t define an addition operator – it’s all hidden in the compiler by calls to String.Concat. (This allows much more efficient concatenation of multiple strings.)