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#include <stdio.h>
#include <stdlib.h>
#include <stdbool.h>
#include <assert.h>
#define print_int_expr_and_value(n)  printf("%s == %d\n", (#n), (n))
#define print_address_expr_and_value(a) printf("%s == %p\n", (#a), (void*)(a))
// WRONG swap_wrong(…)

void swap_wrong(int** a_a_lhs, int** a_a_rhs) {
    // Relative to memory form:  a_a_lhs == 228     a_a_rhs == 236
    int* a_lhs = *a_a_lhs;  // a_a_lhs is an int**      *a_a_lhs is an int*
    int* a_rhs = *a_a_rhs;
    // Relative to memory form:     a_lhs == 220      a_a_rhs == 224
    // Relative to memory form:  *a_a_lhs == 220     *a_a_rhs == 224
    *a_a_lhs = a_rhs;  // "Store a_rhs at (address) a_a_lhs."  // This affects a_n1 not n1.
    *a_a_rhs = a_lhs;  // "Store a_lhs at (address) a_a_rhs."  // This affects a_n2 not n2.
    // Relative to memory form:  a_lhs == 220     a_a_rhs == 224  (no change)
    // Relative to memory form:  *a_a_lhs == 224     *a_a_rhs == 220
}

int main(int argc, char* argv[]) {
    int n1 =   3;
    int n2 = 100;
    print_int_expr_and_value(n1);
    print_int_expr_and_value(n2);

    int* a_n1 = &n1;  // These got swapped.
    assert(*a_n1 == n1);  // obvious
    int* a_n2 = &n2;
    assert(*a_n2 == n2);  // obvious

    print_address_expr_and_value(a_n1);
    print_address_expr_and_value(a_n2);

    swap_wrong(&a_n1, &a_n2);
    assert(*a_n1 == n1);  // shouldn't this obvious????  ... yet this time it fails.
    assert(*a_n2 == n2);  // "

    print_int_expr_and_value(n1);
    print_int_expr_and_value(n2);
    print_address_expr_and_value(a_n1);
    print_address_expr_and_value(a_n2);
    print_int_expr_and_value(*a_n1);
    print_int_expr_and_value(*a_n2);

    /* printf("\nCalled swap_wrong(…)\n"); */

    /* print_int_expr_and_value(n1); */
    /* print_int_expr_and_value(n2); */
    return EXIT_SUCCESS;
}
/* vim: set tabstop=4 shiftwidth=4 fileencoding=utf-8 noexpandtab: */

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