Thread: Order numbers by size, is the solution optimal?

Hello...

I'm learning C++ from "Programming - Principles and Practice using C++", 2nd edition.

In chapter 3, an exercise wants me to:

Write a program that prompts the user to enter three integer values,
and then outputs the values in numerical sequence separated by commas.

So, if the user enters the values 10 4 6, the output should be 4, 6, 10.
If two values are the same, they should just be ordered together.

So, the input 4 5 4 should give 4, 4, 5.

Is the following solution optimal, or can it be written in a more simple way?

Code:

#include "std_lib_facilities.h"

int main()
{
    cout << "Enter three integers, separated by space: ";
    int a, b, c, temp1 = 0, temp2 = 0;
    cin >> a >> b >> c;

    while (a > b || b > c) {
        temp1 = c;
        temp2 = b;
        c = a;
        b = temp1;
        a = temp2;
    }
    cout << a << ", " << b << ", " << c << "\n";
    return 0;
}

UPDATE: My first solution has a bug, so here's the corrected solution,
written using only features I have learned in the first three chapters:

Code:

#include "std_lib_facilities.h"

int main()
{
    cout << "Enter three words, separated by space: ";
    string a, b, c, temp;
    cin >> a >> b >> c;

    if (a > b) {
        temp = a;
        a = b;
        b = temp;
    }
    if (b > c) {
        temp = b;
        b = c;
        c = temp;
    }
    if (a > b) {
        temp = a;
        a = b;
        b = temp;
    }

    cout << a << ", " << b << ", " << c << "\n";
    return 0;
}

Code:

#include <array>
#include <iostream>
#include <algorithm>

int main()
{
	std::array<int, 3> Ints;
	std::cout << "Enter three integers, separated by space: ";
	std::cin >> Ints[0] >> Ints[1] >> Ints[2];
	std::sort(Ints.begin(), Ints.end());
	std::cout << Ints[0] << ", " << Ints[1] << ", " << Ints[2] << "\n";
	return 0;
}

More general form (making it easy to scale for any N):

Code:

#include <array>
#include <iostream>
#include <algorithm>

int main()
{
	std::array<int, 3> Ints;
	std::cout << "Enter three integers, separated by space: ";
	for (size_t i = 0; i < Ints.size(); i++)
		std::cin >> Ints[i];
	std::sort(Ints.begin(), Ints.end());
	for (size_t i = 0; i < Ints.size() - 1; i++)
		std::cout << Ints[i] << ", ";
	std::cout << *(Ints.end() - 1) << "\n";
	return 0;
}

You could test for all 6 possible cases, which minimizes compares and moves depending on the case.

Code:

//
    if (a > b) {
        if(b > c){
            temp = a;   // reverse (swap a c)
            a = c;
            c = temp;
        } else if (a > c){
            temp = a;   // rotate left
            a = b;
            b = c;
            c = temp;
        } else {
            temp = a;   // swap a b
            a = b;
            b = temp;
        }
    } else if (b > c){
        if(a > c){
            temp = a;   // rotate right
            a = c;
            c = b;
            b = temp;
        } else {
            temp = b;   // swap b c
            b = c;
            c = temp;
        }
    }                   // do nothing

Originally Posted by rcgldr

...Once at 4 or more objects, it's better to implement some type of sort algorithm.

Or use one that's already available - std::sort.