I have made program to check through my vector of string to find the corresponding int, which is all fine and well:

int main()
{
    vector<string> letters = {"zero", "one", "two", "three", "four", "five", "six", "seven", "eight", "nine"};
    vector<int> numbers = { 0, 1, 2, 3, 4, 5, 6, 7, 8, 9 };
    string spell;
    cout << "Enter a number spelled-out:\n";
    cin >> spell;
    for (int i = 0; i < letters.size(); ++i) {
        if (spell == letters[i])
            cout << numbers[i] << '\n';
    }
}

Here's the output:

Enter a number spelled-out:
seven
PPP::vector::[]
PPP::vector::[]
PPP::vector::[]
PPP::vector::[]
PPP::vector::[]
PPP::vector::[]
PPP::vector::[]
PPP::vector::[]
PPP::vector::[]
7
PPP::vector::[]
PPP::vector::[]

I wanted to know why is my program reiterating through the vector to check for the corresponding int and showing this in the output?

EDIT: I have discovered the problem. I was using a custom vector from that I got from a header that I was using from the internet. The vector might have something wrong with it. I think I might have allocated the error which might be in this section of code from the header file:

namespace PPP {

using Unicode = long;

// ------- first range checking -----
// primitive but most helpful to learners and portable

template<class T> concept Element = true;

PPP_EXPORT template <Element T>
    class Checked_vector : public std::vector<T> {  // trivially range-checked vector (no iterator checking)
    public:
        using std::vector<T>::vector;

        T& operator[](size_t i)
        {
            std::cerr << "PPP::vector::[]\n";
            return this->std::vector<T>::at(i);
        }

        const T& operator[](size_t i) const
        {
            std::cerr << "PPP::vector::[] const\n";
            return this->std::vector<T>::at(i);
        }
        //  ...
}; // range-checked vector