C++不定数据长度输入问题

#include <iostream>
#include <vector>
using std::vector;
using std::string;
using std::cin;
using std::cout;

int LCS(string s1, string s2) {
    int res = 0;
    int a = 0;
    int b = 0;
    for (int i = 0, j = 0; i < s1.size() && j < s2.size(); i++, j++) {
        if (s1[i] == s2[j])
            res++;
        else
            break;
    }
    return res;
}

int main() {
    int n;
    cin >> n;
    vector<string> s;
    string tmp;
    for (int i = 0; i < n; i++) {
        cin >> tmp;
        s.push_back(tmp);
    }
    vector<vector<int>> num;
    int temp;
    int index = 0;
    ////////////////////输入num，num是二维数组，每一组数据有2个（空格分开）；但是不知道一共有多数组数据从键盘输入////////////////////
   
    while (cin.get()){
        cin >> temp;
        num[index][0] = int(temp);
        cin >> temp;
        num[index][1] = int(temp);
        //num[index][1].push_back(temp);
    }

    for (int i = 0; i < num.size(); i++) {
        int a = num[i][0];
        int b = num[i][1];
        int res = LCS(s[a], s[b]);
        cout << res;
    }
   
}