main.c

#include <stdio.h>
#include <stdlib.h>

/* Memory can be allocated and disallocated dynamically. This allows the
   creation of dynamically sized arrays. The most important functions here
   are 'malloc', 'calloc' and 'free'. */

int main(int argc, char* argv[])
{
    int* a;     /* A (statically allocated) pointer for our array. */
    int n = 5;  /* The size of the array. */

    /* The easiest case using 'malloc': */
    a = (int*)malloc(n * sizeof(int));      /* Dynamically allocate memory. */
                                            /* Malloc needs the size of the memory to be allocated in bytes. It is advisable
                                                to calculate this using sizeof. The return value is of type void*, which is
                                                why it needs to be type casted down to (int*). */
    a[0] = 1;                               /* Now you can use 'a' just like any other array. */
    printf("%i \n", a[0]);
    printf("%i \n", a[1]);                  /* Produces unpredictable output. Never do that. */
    free(a);                                /* Disallocate your memory at the end to avoid memory leaks. */

    /* The easiest case using 'calloc': */
    a = (int*)calloc(n, sizeof(int));       /* Dynamically allocate memory and initialize. */
    printf("%i \n", a[0]);                  /* Gives 0, because 'calloc' initializes the array with 0. */
    free(a);                                /* Disallocate your memory to avoid memory leaks. */

    /* You can create a 2D array as an array of arrays. Here, we create an
       array with m rows and n columns. */
    int** b;
    int m = 2;
    int i;
    b = (int**)malloc(m * sizeof(int*));        /* Memory for the row pointers. */
    for (i = 0; i < m; i++)
        b[i] = (int*)malloc(n * sizeof(int));   /* Memory for the columns. */

    /* Access to a 2D array is like accessing an array of arrays: */
    b[0][1] = 7;                                /* Access row at index 0, column at index 1. */
    printf("%i\n", b[0][1]);

    for (i = 0; i < m; i++)                     /* Don't forget to free all column arrays in the end. */
        free(b[i]);
    free(b);                                    /* Finally free row array. */

    /* You can create arrays of arbitrary dimension in a similar fashion. */

    return 0;
}