How can C#'s string.IndexOf perform so fast, 10 times faster than ordinary for loop find?

Question

I have a very long string (60MB in size) in which I need to find how many pairs of \'<\' and \'>\' are in there.

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I have first tried my own way:

Answer 1

Using a switch statement instead of an if test speeds things up a little also. This code occasionally beats the indexof code on my machine.

        int count = 0;
        bool open = false;
        for (int j = 0; j < testStr.Length; j++)
        {  
            switch (testStr[j])
            {
                case '<':
                    open = true;
                    break;
                case '>':
                    if (open)
                       count++;

                    open = false;
                    break;         
            }
        }