Substring algorithm

Question

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

The problem: given two strings S=S₁S₂S

Answer 1

if (T == string.Empty) return true;
for (int i = 0; i <= S.Length - T.Length; i++) {
    for (int j = 0; j < T.Length; j++) {
        if (S[i + j] == T[j]) {
            if (j == (T.Length - 1)) return true;
        }
        else break;
    }
}
return false;