All the elements of an array's rows have sum = 1

#include <iostream>
#include <stdlib.h>
#include <ctime>
#include <math.h>
#include <vector>
#include <algorithm>

using namespace std;

int main()
{
    srand(time(NULL));
    // 1. Ask the user to give the array's  dimensions
    cout << "Give me the dimensions of an array (m and n must be >= 2).\n";
    int m,n;
    cout << "First, give me m = number of rows: ";
    cin >> m;
    while(m < 2){
        cout << "First, give me m = number of rows: ";
        cin >> m;
    }
    cout << "Now, give me n = number of columns: ";
    cin >> n;
    while(n < 2){
        cout << "Give me n = number of columns: ";
        cin >> n;
    }
    cout << endl << endl;

    // 2. Initialize the array's elements by giving them a first random value
    double matrix[m][n];
    for(int i=0; i<m; i++){
        for(int j=0; j<n; j++){
            // Firstly, each element will be an integer number from 0 to 99 (inclusive)
            matrix[i][j] = rand() % 100;
        }
    }

    // Now, I will show the elements of the array
    cout << "The array in the beginning is this one: " << endl;
    for(int i=0; i<m; i++){
        for(int j=0; j<n; j++){
            cout << matrix[i][j] << " ";
        }
        cout << endl;
    }
    cout << endl << endl;

    // 3. Now, I will create a vector with "m" values = the "m" sums of the "m" rows of the array
    vector <int> sums = vector <int> ();
    for(int i=0; i<m; i++){
        int sum = 0;
        for(int j=0; j<n; j++){
            sum += matrix[i][j];
        }
        sums.push_back(sum);
    }

    // 4. I divide every single element with its row's sum of elements
    for(int i=0; i<m; i++){
        for(int j=0; j<n; j++){
            matrix[i][j] /= sums[i];
        }
    }

    // Now, I will display the final array: each row has sum = 1
    cout << "The final array is this one: " << endl;
    for(int i=0; i<m; i++){
        for(int j=0; j<n; j++){
            cout << matrix[i][j] << " ";
        }
        cout << endl;
    }
    cout << endl << endl;

    // 5. Explaining
    cout << "Because: \n";
    for(int i=0; i<m; i++){
        for(int j=0; j<n; j++){
            if(j != n-1){
                cout << matrix[i][j] << " + ";
            }
            else{
                cout << matrix[i][j] << " = 1" << endl;
            }
        }
    }

    return 0;
}