3.5 Case-Insensitive String Comparison

You want to perform case-insensitive string comparison on two strings.

Technique

Use the overloaded Compare method in the System.String class which accepts a Boolean value, ignoreCase , as the last parameter. This parameter specifies whether the comparison should be case insensitive ( true ) or case sensitive ( false ). To compare single characters , convert them to uppercase or lowercase, using ToUpper or ToLower , and then perform the comparison.

Comments

Validating user input requires a lot of forethought into the possible values a user can enter. Making sure you cover the range of possible values can be a daunting task, and you might ultimately run into human-computer interaction issues by severely limiting what a user can enter. Case-sensitivity issues increase the possible range of values, leading to greater security with respect to such things as passwords, but this security is usually at the expense of a user 's frustration when she forgets whether a character is capitalized. As with many other programming problems, you must weigh the pros and cons.

To perform a case-insensitive comparison, you can use one of the many overloaded Compare methods within the System.String class. The methods that allow you to ignore case issues use a Boolean value as the last parameter in the method. This parameter is named ignoreCase , and when you set it to true , you make a case-insensitive comparison, as demonstrated in Listing 3.6.

Listing 3.6 Performing a Case-Insensitive String Comparison

 using System; namespace _5_CaseComparison {     class Class1     {         [STAThread]         static void Main(string[] args)         {             string str1 = "This Is A String.";             string str2 = "This is a string.";             Console.WriteLine( "Case sensitive comparison of" +                " str1 and str2 = {0}",  String.Compare( str1, str2 ));             Console.WriteLine( "Case insensitive comparison of" +                 " str1 and str2 = {0}", String.Compare( str1, str2, true ));         }     } }