#include <iostream>

// THIS IS CHALLENGING
//
// Given four integers, determine the second-largest value.
//
// For this exercise, "second-largest" does NOT mean the
// second-largest distinct value. Instead, imagine sorting
// the four values from largest to smallest. The
// second-largest value is simply the second value in that
// sorted list.
//
// For example:
//
//     Values          Sorted          Second-largest
//
//     1  1  2  2     2  2  1  1          2
//     1  1  2  3     3  2  1  1          2
//     5  4  1  3     5  4  3  1          4
//     2  5  2  2     5  2  2  2          2
//     1  1  3  1     3  1  1  1          1
//     7  7  7  7     7  7  7  7          7
//     8  8  3  1     8  8  3  1          8
//
// Notice in particular that if the largest value appears
// more than once, the largest and second-largest values
// may be equal.
//
// Write a program that asks the user for four integers and
// prints the second-largest value.
//
// Do not sort the four values. Instead, keep track of the
// largest and second-largest values seen so far.

// Function declarations
int main();

// Function definitions
int main() {
    int a{};
    int b{};
    int c{};
    int d{};

    std::cout << "Enter an integer: ";
    std::cin >> a;

    std::cout << "Enter a second integer: ";
    std::cin >> b;

    std::cout << "Enter a third integer: ";
    std::cin >> c;

    std::cout << "Enter a fourth integer: ";
    std::cin >> d;

    // Determine the second-largest value.

    std::cout << "The second-largest value is "
              << a << std::endl;

    return 0;
}









































// Hint:
//
// Begin with the first two integers.
//
// Determine which is the largest and which is the
// second-largest. Store these in two variables:
//
//     largest
//     second
//
// At this point, these variables should satisfy
//
//     largest >= second.
//
// Now consider the third integer.
//
// There are three possibilities:
//
//     1. It is at least as large as 'largest'.
//
//     2. It is smaller than 'largest' but larger
//        than 'second'.
//
//     3. It is no larger than 'second'.
//
// In which of these cases must 'largest' or 'second'
// be changed?
//
// Once you have correctly processed the third integer,
// repeat the same procedure for the fourth integer.









































// A useful way to think about the algorithm is to
// maintain the following statement:
//
//     'largest' is the largest value seen so far,
//     and 'second' is the second-largest value seen
//     so far.
//
// After processing each new value, this statement
// should still be true.
//
// Such a statement is called an invariant.









































// Here is one solution:

/*
int main() {
    int a{};
    int b{};
    int c{};
    int d{};

    int largest{};
    int second{};

    std::cout << "Enter an integer: ";
    std::cin >> a;

    std::cout << "Enter a second integer: ";
    std::cin >> b;

    // Initialize 'largest' and 'second' using the first
    // two values.

    if ( a >= b ) {
        largest = a;
        second = b;
    } else {
        largest = b;
        second = a;
    }

    // We now know that 'largest' and 'second' are the
    // largest and second-largest of the first two values.

    std::cout << "Enter a third integer: ";
    std::cin >> c;

    if ( c >= largest ) {
        // The old largest becomes the second-largest,
        // and 'c' becomes the new largest.

        second = largest;
        largest = c;
    } else if ( c > second ) {
        // The largest remains unchanged, but 'c'
        // becomes the new second-largest.

        second = c;
    }

    // If neither condition was true, then
    //
    //     c <= second,
    //
    // so neither value needs to change.

    std::cout << "Enter a fourth integer: ";
    std::cin >> d;

    if ( d >= largest ) {
        // The old largest becomes the second-largest,
        // and 'd' becomes the new largest.

        second = largest;
        largest = d;
    } else if ( d > second ) {
        // The largest remains unchanged, but 'd'
        // becomes the new second-largest.

        second = d;
    }

    // If neither condition was true, then
    //
    //     d <= second,
    //
    // so neither value needs to change.

    std::cout << "The second-largest value is "
              << second << std::endl;

    return 0;
}
*/