How to Sort an Array in C++?

Last Updated : 10 Oct, 2024

Sorting an array involves rearranging its elements in a specific order such as from smallest to largest element or from largest to smallest element, etc. In this article, we will learn how to sort an array in C++.

Example:

Input: arr ={5,4,1,2,3}
Output: 1 2 3 4 5
Explanation: arr is sorted in increasing order
Input: arr ={3,2,5,4,1}
Output: 5 4 3 2 1
Explanation: arr is sorted in decreasing order

Sort an Array using Library Function

C++ STL provides std::sort() method which is used to sort the array in any desired order. This function uses a combination of quicksort, insertion sort and heapsort algorithm. The default sorting order is ascending order, but we can also provide the custom comparator as the third parameter to sort in user defined order.

Syntax

std::sort(arr, arr + n);

where arr is the array to be sorted and n is the size of the array.

Code Implementation

C++

// C++ Program to how to sort an array using
// std::sort() function
#include <bits/stdc++.h>
using namespace std;

int main() {
    int arr[] = {5, 4, 1, 2, 3};

    // Calculate the size of the array
    int n = sizeof(arr) / sizeof(arr[0]);

    // Sort the array using std::sort()
    sort(arr, arr + n);

    for (auto i : arr)
        cout << i << " ";
    return 0;
}

Output

1 2 3 4 5

Time Complexity: O(n log n), where n is the size of the array.
Auxiliary Space: O(log n)

Table of Content

Other Method to sort an Array in C++

Using Bubble Sort
Using Selection Sort

Other Method to sort an Array in C++

To use other sorting algorithm apart from std::sort(), you have to manually implement it.

Using Bubble Sort

In Bubble Sort Algorithm, we repeatedly swap adjacent elements if they are in the wrong order. This process is repeated until the array is sorted.

C++

// C++ Program to sort an array using bubble sort
#include <bits/stdc++.h>
using namespace std;

// Function to perform bubble sort
void bubbleSort(int arr[], int n) {
    for (int i = 0; i < n - 1; i++) {
        for (int j = 0; j < n - i - 1; j++) {
          
            // Swap if the element found is
          	// greater than the next element
            if (arr[j] > arr[j + 1]) 
                swap(arr[j],arr[j+1]);
        }
    }
}

int main() {
    int arr[] = {5, 4, 3, 2, 1};
    int n = sizeof(arr) / sizeof(arr[0]);

    // Sort arr using bubble sort
    bubbleSort(arr, n);

    for (auto i : arr)
        cout << i << " ";

    return 0;
}

Output

1 2 3 4 5

Time Complexity: O(n²), where n is the size of the array.
Auxiliary Space: O(1)

Using Selection Sort

Selection sort is a simple sorting algorithm that repeatedly finds the minimum element from the unsorted part of the array and places it at its position in the sorted part of the array until the complete array is sorted.

C++

// C++ Program to sort an array using selection sort
#include <bits/stdc++.h>
using namespace std;

void selectionSort(int arr[], int n) {
    for (int i = 0; i < n - 1; i++) {
      
        // Assume current index as minimum element
        int min = i;

        // Find the minimum element in the remaining
        // unsorted array
        for (int j = i + 1; j < n; j++) {
            if (arr[j] < arr[min])
                min = j;
        }
        // If the new minimum element found, swap
      	/// it with current index
       if (min != i) {
            swap(arr[i],arr[min]);
        }
    }
}
int main() {
    int arr[] = {5, 4, 3, 2, 1};
    int n = sizeof(arr) / sizeof(arr[0]);
  
    // Sort arr using selection sort
    selectionSort(arr,n);
    
    for (auto i: arr)
        cout<<i<<" ";
    return 0;
}

Output

1 2 3 4 5

Time Complexity: O(n²), where n is the size of the array.
Auxiliary Space: O(1)