How to find substring from string without using indexof method in C#?

Question

I want to find the position of a substring in a string if present without using any string method including indexof. I tried so much times but failed. Will anybody tell me h

Answer 1

        string mainString = Console.ReadLine();
        string subString = Console.ReadLine();
        for (int i = 0; i <= mainString.Length - subString.Length; i++)
        {
            bool match = true;
            for (int j = 0; j < subString.Length && mainString[i + j] != subString[j]; j++)
            {
                match = false;
            }
            if (match)
                Console.WriteLine(i);
        }