Question

how can I Check if a string contains another string?

Answer 1

Why iterate when you can use LINQ? I think you’re asking to get all the strings that are substrings of other strings in the array (please correct me if I’m wrong):

var result = strings.Where(s => strings.Any(s2 => s2.Contains(s)));

Update

After your update, the question seems much easier than original. If you just want to find out if a string contains another string, just use the Contains method:

var s = "Hello World!";
var subString = "Hello";

var isContained = s.Contains(subString);

Or if you want to do a case insensitive search, you have to do things a little differently:

var s = "Hello World!";
var subString = "hello";

var isContained = s.IndexOf(subString, 
    StringComparison.InvariantCultureIgnoreCase) > 0;