Task8.cpp

#include <iostream>
#include <string>
using namespace std;

int findSubstring(string sub, string mainString) {
    if (sub.empty() || mainString.empty()) { // if the substring or main string is empty, we return -1
        cout << "The substring or main string is missing ";
        return -1;
    }

    int start = -1;  // will hold the starting index of the match if found
    int matchIndex = 0;  // tracks progress through the substring

    for (int i = 0; i < mainString.length(); i++) {
        if (mainString[i] == sub[matchIndex]) {// if current characters match, move to next character of substring
            if (matchIndex == 0) { // record potential starting index of the match
                start = i;
            }
            matchIndex++;

            if (matchIndex == sub.length()) {// if full substring matched, return the starting index
                return start;
            }
        } else { // mismatch: reset the substring index
            if (matchIndex > 0) {
                i = i - matchIndex;
            }
            matchIndex = 0;
            start = -1;
        }
    }

    return -1; // substring not found
}

int main() {
    string substring = "dib"; 
    string t1 = "dibilical"; // test case 1
    string t2 = "icaldib";   // test case 2
    string t3 = "testString"; // test case 3
    string t4 = "dildil";    // substring partially matches 

    cout << "Test case 1: " << findSubstring(substring, t1) << endl;
    cout << "Test case 2: " << findSubstring(substring, t2) << endl;
    cout << "Test case 3: " << findSubstring(substring, t3) << endl;
    cout << "Test case 4: " << findSubstring(substring, t4) << endl;
    cout << "Test case 5: " << findSubstring("", t4) << endl;
    cout << "Test case 6: " << findSubstring(substring, "") << endl;
    return 0;
}