#include <iostream>

/****************************************************
 * This program demonstrates what may happen when
 * you access entries outside the bounds of an array.
 *
 * IMPORTANT:
 *
 * Accessing an array outside its bounds results in
 * undefined behavior. Nothing demonstrated by this
 * program is guaranteed by C++.
 *
 * In one particular execution of this program, the
 * compiler happened to allocate memory approximately
 * as follows:
 *
 * 0x7ff...0dc     n          <- initially 91
 * 0x7ff...0e0     array[0]
 * 0x7ff...0e4     array[1]
 * 0x7ff...0e8     array[2]
 * 0x7ff...0ec     array[3]
 * 0x7ff...0f0     array[4]
 * 0x7ff...0f4     array[5]
 * 0x7ff...0f8     array[6]
 * 0x7ff...0fc     array[7]
 * 0x7ff...100     array[8]
 * 0x7ff...104     array[9]
 * 0x7ff...108     m          <- initially 42
 *
 * With this particular arrangement, it appeared that
 *
 *     array[-1]
 *
 * accessed the memory occupied by n, while
 *
 *     array[10]
 *
 * accessed the memory occupied by m.
 *
 * Again, this is not guaranteed. A different compiler,
 * different compiler options, or even another execution
 * of the same program may produce different results.
 *
 * The only valid indices for array are 0 through 9.
 ****************************************************/

int main() {
    std::cout << "Initializing 'm' with the value 42..."
              << std::endl;
    int m{ 42 };

    int array[10];

    std::cout << "Initializing 'n' with the value 91..."
              << std::endl;
    int n{ 91 };

    std::cout << "   m = " << m << std::endl;
    std::cout << "   n = " << n << std::endl;

    std::cout << std::endl;

    std::cout << "      &m = " << &m     << std::endl;
    std::cout << "   array = " <<  array << std::endl;
    std::cout << "      &n = " << &n     << std::endl;

    std::cout << std::endl;

    std::cout << "Assigning array[k] the value k"
              << std::endl;
    std::cout << "for k = -1, 0, 1, ..., 10."
              << std::endl;

    // WARNING:
    //
    // The assignments for k == -1 and k == 10
    // access memory outside the array and therefore
    // result in undefined behavior.
    for ( int k{ -1 }; k <= 10; ++k ) {
        array[k] = k;
    }

    std::cout << std::endl;

    std::cout << "   m = " << m << std::endl;
    std::cout << "   n = " << n << std::endl;

    std::cout << std::endl;

    std::cout << "Assigning 'm' the value 150..."
              << std::endl;
    m = 150;

    std::cout << "Assigning 'n' the value 250..."
              << std::endl;
    n = 250;

    std::cout << std::endl;

    // WARNING:
    //
    // Similarly, reading array[-1] and array[10]
    // results in undefined behavior.
    for ( int k{ -1 }; k <= 10; ++k ) {
        std::cout << "   array[" << k << "] = "
                  << array[k] << std::endl;
    }

    return 0;
}