How can I check if a string contains a character in C#?

Question

Is there a function I can apply to a string that will return true of false if a string contains a character.

I have strings with one or more character options such as:

var abc = "s"; var def = "aB"; var ghi = "Sj"; 

What I would like to do for example is have a function that would return true or false if the above contained a lower or upper case "s".

if (def.Somefunction("s") == true) { } 

Also in C# do I need to check if something is true like this or could I just remove the "== true" ?

Answer 1

You can use the extension method .Contains() from the namespace System.Linq:

using System.Linq;      ...      if (abc.ToLower().Contains('s')) { } 

And also, to check if a boolean expression is true, you don't need == true

Since the Contains method is an extension method, my solution might be confusing. Here are two versions that don't require you to add using System.Linq;:

if (abc.ToLower().IndexOf('s') != -1) { }  // or:  if (abc.IndexOf("s", StringComparison.CurrentCultureIgnoreCase) != -1) { } 

Update

If you want to, you can write your own extensions method for easier reuse:

public static class MyStringExtensions {     public static bool ContainsAnyCaseInvariant(this string haystack, char needle)     {         return haystack.IndexOf(needle, StringComparison.InvariantCultureIgnoreCase) != -1;     }          public static bool ContainsAnyCase(this string haystack, char needle)     {         return haystack.IndexOf(needle, StringComparison.CurrentCultureIgnoreCase) != -1;     } } 

Then you can call them like this:

if (def.ContainsAnyCaseInvariant('s')) { } // or if (def.ContainsAnyCase('s')) { } 

In most cases when dealing with user data, you actually want to use CurrentCultureIgnoreCase (or the ContainsAnyCase extension method), because that way you let the system handle upper/lowercase issues, which depend on the language. When dealing with computational issues, like names of HTML tags and so on, you want to use the invariant culture.

For example: In Turkish, the uppercase letter I in lowercase is ı (without a dot), and not i (with a dot).