C++ Exercises: Prints the word and a list of the corresponding page numbers

#include <iostream>
#include <vector>
#include <algorithm> // Required for sort()
using namespace std;

// Define a pair alias for string and int
typedef pair<string, int> P;

int main()
{
    string str;
    int page, ctr = 0;
    vector<P> v_data; // Vector of pairs to store string and int pairs

    // Input loop: Read string and integer pairs until the end of input
    while (cin >> str >> page) {
        v_data.push_back(P(str, page)); // Store the pair (string, int) in the vector
        ctr++;
    }

    // Sort the vector of pairs based on string (lexicographical order)
    sort(v_data.begin(), v_data.end());

    // Loop through the sorted vector of pairs
    for (int i = 0; i < ctr; i++) {
        if (i == 0) {
            cout << v_data[i].first << endl; // Print the first string
            cout << v_data[i].second; // Print the first associated integer
            continue;
        }

        // Check if the current string is the same as the previous string
        if (v_data[i].first == v_data[i - 1].first && v_data[i].second != v_data[i - 1].second) {
            cout << ' ' << v_data[i].second; // If the strings match but integers don't, print the current integer
            continue;
        } else {
            cout << endl; // Print a newline when the strings differ
        }

        cout << v_data[i].first << endl; // Print the current string
        cout << v_data[i].second; // Print the associated integer
    }

    puts(""); // Print a newline at the end
    return 0;
}