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

int main(int argc, char** argv) {
    int* a_n = malloc(sizeof *a_n);  // equivalent to malloc(4) but always use expression.
    // malloc(…) takes a number of bytes to allocate.
    // ... and returns an address (void*) on the heap.
    //  - In C, you can assign a void* to an ▒▒* and vice versa (as long as one is void*).
    //  - The memory will be continguous (all together)
    //  -  ... and NOT initialized to anything in particular.
    
    *a_n = 5;                      // "store 5 at address a_n"
    printf("*a_n == %d\n", *a_n);  // "print the value at address a_n."
                                   //
    free(a_n);
    // free(…) takes a memory address
    //  - Address must be an address previously returned by malloc(…).
    //  - That address will be on the heap.
    //  - You must call free exactly once for every call to malloc.

    return EXIT_SUCCESS;
}

    
    // WRONG:  int* a_n = malloc(sizeof(int));
    //
    // sizeof *a_n  ⇔  sizeof(*a_n)  ⇔  sizeof(int)
    // sizeof is an operator not a function or macro
    // sizeof takes an expression or a type... always use an expression if possible
    //
    // WRONG:  int* a_n = (int*) malloc(sizeof(…));
    //
    // Do not use typecasts unless you can articular why it is necessary and safe.
    // The cases where a typecast is necessary and safe are few and far between.

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