how to check if any letter of a string in c# code example

Example 1: c# check if string is only letters and numbers

if (textVar.All(c => Char.IsLetterOrDigit(c))) {
    // String contains only letters & numbers
}

Example 2: c# check if string contains value

string s1 = "The quick brown fox jumps over the lazy dog";
string s2 = "fox";
bool b = s1.Contains(s2);
Console.WriteLine("'{0}' is in the string '{1}': {2}",
                s2, s1, b);
if (b) {
    int index = s1.IndexOf(s2);
    if (index >= 0)
        Console.WriteLine("'{0} begins at character position {1}",
                      s2, index + 1);
}
// This example displays the following output:
//    'fox' is in the string 'The quick brown fox jumps over the lazy dog': True
//    'fox begins at character position 17