c++ check substring

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

int main() {
    string str = "Hello, world!";
    string sub = "world";

    size_t found = str.find(sub);
    if (found != string::npos) {
        cout << "Subtring found at position: " << found << endl;
    } else {
        cout << "Substring not found" << endl;
    }

    return 0;
}