User Input in 2-D array of dynamic size in C++

Question

I am trying to create a 2-D vector that as column 0 it would have integers and column 1 would have vectors.

For example:

column[0]  column[1]
2          {2}
5          {1,2,0}
12         {4,7,9,0,0,1,6,0,0}
3          {6}

column 0 would be user input while column 1 I will calculate it on my own - I don't mind if it has dummy vectors for now and after the user exits then it would print the 2-D vector. What I tried is:

int main() {
    unsigned int input;
    vector<vector<unsigned int>> v;
    while (cin >> input) // enter non int to exit
        for(int i=0; i<input;i++){
            vector<int> factorial; //calc in a separate function - dummy vector for now
            for (int j=0; j<factorial.size(); j++){
                v[i].push_back(input); //set column 0 as input
                v[i][j].push_back(factorial); //set column 1 as the vector containing the factorial of input
            }
        }
 return 0;
}

Answer 1

Seems like you need to use class:

#include <iostream>
#include <vector>

using namespace std;

template<class T1, class T2>
class Columns{
public:
    vector<T1> input;
    vector<T2> output;
};

int main(){
    Columns<int, int> columns; //Or, if you need to have vector in "output": \
                                 Columns<int, vector<int>> columns;
    //Usage:
    columns.input.push_back(2);
    columns.output.push_back(2);
    return 0;
}

---

But, if you need more shortest implementations, you can use map:

#include <iostream>
#include <vector>
#include <map>

using namespace std;

int main(){
    map<int, vector<int>> result;
    for(int i = 0; i < 10; i++)
        result[i] = factorial(i); //Where factorial() is function that returns vector
    for(auto res: result){
        cout << "Input: " << res.first << "; Result: {";
        for(auto res2: res.second)
            cout << res2 << "; ";
        cout << "};" << endl;
    }
}

So in "map" case, output should be like this:

Input: 0; Result: {Numbers here};
...
Input: 9; Result: {Numbers here};

---

Otherwise, you can just use 2 different arrays or vectors:

Maybe, it's the best option for you now.

#include <iostream>
#include <vector>

using namespace std;

template<class T>
vector<T> FactorialNumbers(T input){
    vector<T> result;
    for((input < 0) ? return result : input = input; input != 0; input--)
        result.push_back(input);
    return result;
}

int main() {
    vector<int> input;
    vector<vector<int>> output;

    int usrInput = 0;
    while(cin >> usrInput){
        input.push_back(usrInput);
        output.push_back(FactorialNumbers(usrInput));
    }
}

And if you work with int only, you can change FactorialNumbers like this:

int FactorialNumbers(int input){
    vector<int> result;
    for((input < 0) ? return result : input = input; input != 0; input--)
        result.push_back(input);
    return result;
}

---

You can also try: vector<pair<int, std::vector<int>>>