P.1: The index result of a `std::find`-like loop needs to be initialized to -1.

CppCoreGuidelines.md

@@ -370,7 +370,7 @@ The second version leaves the reader guessing and opens more possibilities for u
         string val;
         cin >> val;
         // ...
-        int index = 0;            // bad
+        int index = -1;            // bad
         for (int i = 0; i < v.size(); ++i)
             if (v[i] == val) {
                 index = i;