Changing the case of characters within a String C# with Example

The System.String class supports a number of methods to convert between uppercase and lowercase characters 
in a string. 
System.String.ToLowerInvariant is used to return a String object converted to lowercase. 
System.String.ToUpperInvariant is used to return a String object converted to uppercase. 
Note: The reason to use the invariant versions of these methods is to prevent producing unexpected culture- 
specific letters. This is explained here in detail. 
Example: 
string s = "My String"; 
 

s = s.ToLowerInvariant(); //  "my  string" 
s = s.ToUpperInvariant(); // "MY STRING" 
Note that you can choose to specify a specific Culture when converting to lowercase and uppercase by using the 
String.ToLower(CultureInfo) and String.ToUpper(CultureInfo) methods accordingly.