How to create an array inside another array?

I need to know how to make a list of lists, something like in python and dictionaries, where they gave you an entry and returned the values. In other examples, something like creating a list of students and each student having their average A and their average B. (Student -- [average A , average B]. With that data then, based on user input, print the value and either averageA or averageB. An input like:
input:
Student: Pedro

Output:
AverageA: 15
AverageB: 17

From my program I tried doing this but it only gives me an error.

#include <iostream>
#include <iomanip>
using namespace std;

void azar(int planetas[]){

}
int main(){
    int planetas; int Mercurio[2] = {0.5, 0.3};
    int** sistema = new int*[planetas]; 
    for(int i = 0; i < 4; i++){
        for(int j = 0; j < 4; j++){
            sistema[i][j] = Mercurio;
            cout << sistema[i][j];
        }
    }
}