Sort an array in descending order in C++

This post will discuss how to sort an array in descending order in C++.

To sort an array in reverse/decreasing order, you can use the std::sort algorithm provided by STL. It sorts the elements of a container in the range pointed by the specified iterators using a comparator. The default comparator used is std::less<>, which sorts the container in ascending order using operator<. We can use std::greater<> to sort in descending order, which delegates the call to operator>.

#include <iostream>

#include <algorithm>

int main()

{

int arr[] = { 3, 5, 2, 4, 7 };

std::sort(std::begin(arr), std::end(arr), std::greater<>());

// pass the template argument <int> to `std::greater` before C++14;

// otherwise, the code won't compile

for (int const &i: arr) {

std::cout << i << ' ';

}

return 0;

}

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Output:

7 5 4 3 2

We can also pass a custom comparator to the sort function. The custom comparator should be a binary predicate that compares its two arguments and return a bool that determines whether the first argument goes before the second argument in the sorted array. We can pass the custom comparator to the sort() function in many ways:

1. We can use an instance of a class implementing the () operator as a comparison function.

#include <iostream>

#include <algorithm>

struct comp {

bool operator()(int const &i, int const &j) const {

return i > j;

}

};

int main()

{

int arr[] = { 3, 5, 2, 4, 7 };

std::sort(std::begin(arr), std::end(arr), comp());

// code to print the array

return 0;

}

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Output:

7 5 4 3 2

2. We can also use a binary function that accepts two elements as arguments and returns true if the first argument is less than the second argument.

#include <iostream>

#include <algorithm>

int comp(int const &i, int const &j) {

return i > j;

}

int main()

{

int arr[] = { 3, 5, 2, 4, 7 };

std::sort(std::begin(arr), std::end(arr), comp);

// code to print the array

return 0;

}

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Output:

7 5 4 3 2

3. With C++11, we can even pass a lambda to the std::sort function to define the ordering.

#include <iostream>

#include <algorithm>

int main()

{

int arr[] = { 3, 5, 2, 4, 7 };

std::sort(std::begin(arr), std::end(arr),

[](auto const &i, auto const &j) {

return i > j;

});

// code to print the array

return 0;

}

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Output:

7 5 4 3 2

That’s all about sorting an array in descending order in C++.