concatinate string

you can use Concat Method to Concat two value as given below

ListBox1.Items.Add(String.Concat(TextBox1.Text, TextBox2.Text))

String.concat function is used to creates the string representaion of Specified object

For Concatenate strings use this[^]

You can use String.Concat as Ravi said because it's just 2 strings, for massive concatenation I recommend StringBuilder

use the Concat() method to concatenate strings

http://msdn.microsoft.com/en-us/library/system.string.concat%28VS.71%29.aspx[^]