Объяснить строки кода

#include <iostream>
#include <ctime>
#include <iomanip>
using namespace std;
const int N = 10;
const int M = 10;
 
void fill(int arr[N][M], int arr_for_fill[N], int n, int m, int a, int b) {
    for (int i = 0; i < n; i++) {
        for (int j = 0; j < m; j++) {
            arr[j][i] = arr_for_fill[i];
        }
    }
}
 
void write_first(int& n, int& m) {
    while (true) {
        cout << "Write n and m" << endl;
        cin >> n >> m;
        if (n > N || m > M) {
            cout << "Number what you write is too high, n <= 10 and m <= 10, try again" << endl;
            continue;
        }
        else {
            return;
        }
    }
}
 
void write_second(int& a, int& b) {
    while (true) {
        cout << "Write a and b to fill array " << endl;
        cin >> a >> b;
        if (a >= b) {
            cout << "a >= b, a need to be smaller than b, try again" << endl;
            continue;
        }
        else {
            return;
        }
    }
}
 
 
int main() {
    srand(time(0));
    int arr[N][M];
    int n, m, a, b;
    write_first(n, m);
    write_second(a, b);
    int arr_for_fill[N];
    for (int i = 0; i < n; i++) {
        arr_for_fill[i] = rand() % (b - a + 1) + a;
    }
    fill(arr, arr_for_fill, n, m, a, b);
    cout << endl;
    cout << "n = " << n << " m = " << m << endl;
    cout << "Gap was [" << a << ", " << b << "]" << endl;
    cout << "Matrix: " << endl;
    for (int i = 0; i < n; i++) {
        for (int j = 0; j < m; j++) {
            cout << setw(5) << arr[i][j];
        }
        cout << endl;
    }
}