Substring algorithm

Question

Can someone explain to me how to solve the substring problem iteratively?

The problem: given two strings S=S₁S₂S

Answer 1

Is a O(n*m) algorithm, where n and m are the size of each string. In C# it would be something similar to:

   public static bool IsSubtring(char[] strBigger, char[] strSmall)
        {
            int startBigger = 0;
            while (startBigger <= strBigger.Length - strSmall.Length)
            {
                int i = startBigger, j = 0;

                while (j < strSmall.Length && strSmall[j] == strBigger[i])
                {
                    i++;
                    j++;
                }

                if (j == strSmall.Length)
                    return true;
                startBigger++;
            }

            return false;
        }