C :: Adding Two Matrix Using Malloc

This is my code without malloc. I need to change the array size so there is no max size for each matrix. I must dynamically allocate space for all arrays used. So I need to use malloc to create my arrays. So I cant use int A[rows][cols].

Code:

/* This program asks the user for 2 matrices called A and B, as integers, and displays their sum, C. The max dimension of each matrix is 100. */
#include<stdio.h>
// Construct function
void construct()
{
int m, n, i, j;// Variables
int first[100][100], second[100][100], sum[100][100];// Matrices variables

[Code]...

Im having a hard time understanding/using malloc. Should first, second, and sum be single pointers or double? How do I scan the matrix correctly? And how do I add them properly? Do I have to change my for loops?

Code:

/* This program asks the user for 2 matrices called A and B, as integers, and displays their sum, C. The max dimension of each matrix is 100. */
#include <stdio.h>
#include <stdlib.h>
// Construct function
void construct()

[Code]...