# C++ STL sort function to sort an array or vector

In this article we are going to learn how we can use STL sort function to sort array or vector in C++?
Submitted by Radib Kar, on December 02, 2018

## STL sot function

C++ STL has a default sort function which sort an array or vector in increasing order. Normally it uses quick sort which has a worst case time complexity of O(n^2) and average of O(nlogn).

To sort an array:

Let the array be a[n] that mean the length of the array is n. To sort the array we need to write sort(a,a+n);

To sort a vector:

```    vector<int> a; //a vector of integer type
```

To sort the vector in increasing order we need to write

```    sort(a.begin(),a.end());
```

## C++ implementation of sort function to sort an array or vector

```#include <bits/stdc++.h>
using namespace std;

int main ()
{
//sorting an array
cout<<"............sorting an array............"<<endl;
//array defined
int arr[10] = { 34, 67, 54, 2, 4, 78, 63, 90, 12, 26 };

cout << "before sorting......." << endl;
for (int i = 0; i < 10; i++)
cout << arr[i] << " ";
cout << endl;

cout << "after sorting.........." << endl;
sort (arr, arr + 10);		//using STL sort function
for (int i = 0; i < 10; i++)
cout << arr[i] << " ";
cout<<endl;

//sorting a vector
cout<<"............sorting a vector............"<<endl;
vector<int> a;
a.push_back(6);
a.push_back(5);
a.push_back(12);
a.push_back(25);
a.push_back(1);
a.push_back(87);
a.push_back(34);
a.push_back(16);
cout << "before sorting......." << endl;

for(auto it=a.begin();it!=a.end();it++){
cout<<*it<<" ";
}
cout<<endl;

sort(a.begin(),a.end());//using STL sort function
cout << "after sorting......." << endl;

for(auto it=a.begin();it!=a.end();it++){
cout<<*it<<" ";
}
cout<<endl;

return 0;
}
```

Output

```............sorting an array............
before sorting.......
34 67 54 2 4 78 63 90 12 26
after sorting..........
2 4 12 26 34 54 63 67 78 90
............sorting a vector............
before sorting.......
6 5 12 25 1 87 34 16
after sorting.......
1 5 6 12 16 25 34 87
```

Preparation