Concatenating

There are a couple of ways you can concatenate strings.

System.String.ConCat

string sName; 
sName = System.String.Concat("firstname", "lastname"); 

+ and += (with double quotes)

string sName; 
sName = "firstname" + "lastname" 
sName = sName + "somethingelse" 
sName += "somethingelse 

& and &= (with double quotes)

string myString; 
myString = "firstname" & "lastname" 

This can be used to amend a string to itself plus something else

sName = sName & "something else" 
sName &= "something else" 

System.String.Join

Concatenates all the elements of a string array using a given separator

String.Join(seperator as string, 
      value() as string) as string 
String.Join(seperator as string, 
       value() as string, _ 
      startindex as Integer, _ 
     count as Integer) as string 

StringBuilder

Everytime you concatenate a string a new address in memory is allocated
The existing string is copied to a new location with the newly string added
When you use StringBuilder the same position in memory is used

StringBuilder oStringBuilder = new StringBuilder(); 
foreach (var value in mystring) 
{ 
   oStringBuilder.Append(value) 
} 

Important

In VB.Net you can also use the plus (+) sign as a concatenation operator but this should be avoided as it is also used for adding numeric values.