3 integers from greatest to least

Question

I am beginner to C++ and I using \"Programming: Principles and Practice Using C++ (Second Edition). The question asked: \"Write a program that prompts the user to enter three in

Answer 1

std::sort (as suggested by Richard) is one solution, though IMHO such heavy gun isn't necessary for a data set of 3 elements. For 3 variables, the sorting can be unrolled (as the OP tried) and the various available sorting algorithms probably differ that much (concerning the order of comparisons and swaps) or won't bring any improvement concerning this little sample.

Thus, I made an unrolled sort (re-sembling what I believe would be bubble sort):

#include <iostream>

void sort(int &a, int &b, int &c)
{
  if (a < b) std::swap(a, b);
  if (b < c) std::swap(b, c);
  if (a < b) std::swap(a, b);
}

int main()
{
  // any permutation of { 1, 2, 3 } (i.e. any possible order)
  int tests[][3] = {
    { 1, 2, 3 },
    { 1, 3, 2 },
    { 2, 1, 3 },
    { 2, 3, 1 },
    { 3, 1, 2 },
    { 3, 2, 1 }
  };
  // apply sort() to every test set
  for (int *test : tests) {
    int a = test[0], b = test[1], c = test[2];
    std::cout << "a: " << a << " b: " << b << " c: " << c << " sorted: ";
    sort(a, b, c);
    std::cout << "a: " << a << " b: " << b << " c: " << c << '\n';
  }
  // done
  return 0;
}

Output:

a: 1 b: 2 c: 3 sorted: a: 3 b: 2 c: 1
a: 1 b: 3 c: 2 sorted: a: 3 b: 2 c: 1
a: 2 b: 1 c: 3 sorted: a: 3 b: 2 c: 1
a: 2 b: 3 c: 1 sorted: a: 3 b: 2 c: 1
a: 3 b: 1 c: 2 sorted: a: 3 b: 2 c: 1
a: 3 b: 2 c: 1 sorted: a: 3 b: 2 c: 1

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