Check if a string start with any character in a list

If your character "list" is definitely going to be a char[], I would assume you're best off with:

return toCheck.IndexOfAny(columnChars) == 0;

Disclaimer: I haven't benchmarked this. But that method's just sitting there.

Turn the check around and see if the first character is in the allowable set.

 char[] columnChars = new char[] { 'A', 'B', 'C', 'D', 'E' };
 private bool startWithColumn(string toCheck)
 {
     return toCheck != null
                && toCheck.Length > 0
                && columnChars.Any( c => c == toCheck[0] );
 }

You can get the first character out of a string easily enough:

char c = toCheck[0];

And then check whether it's in the array:

return columnChars.Contains(c);

I needed something similar, but for strings:

I wanted to know if my string subject started with any of these strings:

var qualent3s = new string[] { "D", "M", "H", "JUK"};

The LINQ to do so is simple:

qualent3s.Any(x => subject.StartsWith(x))