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

// malloc(…) allocates memory (i.e., reserves space) on the HEAP for 
// whatever you want to store.  Unlike arrays on the stack, you specify
// the "buffer size" (i.e., amount of memory) at runtime (i.e., with a 
// variable while the program is running).
// 
// malloc(«number of bytes») → returns the address of the first byte in
//                             the newly allocated buffer (your new space).
//
// Use this form:
// «TYPE»* «VARIABLE» = malloc(«num of elements» * sizeof(*«VARIABLE»));
// ∙ Do not use a cast.
// ∙ Do not use sizeof(«TYPE»).  Use sizeof(*«VARIABLE») instead.
//                               Use sizeof(*«VARIABLE») instead.
//                               Use sizeof(*«VARIABLE») instead.
//                               … because *«VARIABLE» is of type «TYPE»

// With malloc(…) you can decide your needs at runtime.
//                space does not go away after the function returns.
// You MUST free(…) the space using free(«address»).
// free(…) must be called EXACTLY once for each call to malloc(…).

int main(int argc, char* argv[]) {
    int* a_n = malloc(sizeof(*a_n));
    // Allocate space for one int on the HEAP.
    
    *a_n = 20;

    // "LOCATION A"

    printf("*a_n = %d\n", *a_n);        // log_int(*a_n)
    printf(" a_n = %p\n", (void*)a_n);  // log_addr(a_n)

    free(a_n);

    return EXIT_SUCCESS;
}
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