Length of a String without using in-built methods (like Length)

Sometime we have to get length of string but we don't have to use in-built method like Length in c#.

Let's make a method to get length of string

public int LengthOfString(string _strkey)
        {
            int _length = 0;
            bool isTrue = false;
            do
            {
                try
                {
                    char _char = _strkey[_length];
                    _length++;
                }
                catch (IndexOutOfRangeException)
                {
                    isTrue = true;
                }
            }
            while (!isTrue);
            {
                return _length;
            }

        }