Sorting a vector in C++ | Board Infinity

A vector in C++ is similar to dynamic arrays which are capable of resizing itself if required. The C++ stl provides us sort() inbuilt function to sort a vector

Sorting a vector in ascending order

The following syntax sorts a vector in ascending order:

Syntax

sort(vector.begin(), vector.end())

The above syntax sorts a vector in ascending order. Let us consider the following program,

Source Code

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

int main() {

// Create a vector
vector<int> myVector = {10,30,40,20};

// Push back 90 at the end of the vector
myVector.push_back(90);

// Push back 80 at the end of the vector
myVector.push_back(80);

// Sort the vector
sort(myVector.begin(), myVector.end());

for(auto it = myVector.begin() ; it != myVector.end() ; it++)
{
cout << (*it) << ' ';
}

return 0;
}

Output

Output Description

As you can see, the vector has been sorted in ascending order.

Sorting a vector in descending order

The sort() function accepts a third argument that sorts the vector in descending order. Its syntax is given below,

Syntax

sort(myVector.begin(), myVector.end(), greater<int>())

Let us consider the following program:

Source Code

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

int main() {

// Create a vector
vector<int> myVector = {10,30,40,20};

// Push back 90 at the end of the vector
myVector.push_back(90);

// Push back 80 at the end of the vector
myVector.push_back(80);

// Sort the vector
sort(myVector.begin(), myVector.end(), greater<int>());

cout << "myVector: { ";
for(auto it = myVector.begin() ; it != myVector.end() ; it++)
{
cout << (*it) << ' ';
}

cout << "}";

return 0;
}

Output:

Output Description

As you can see in the output, the vector has been sorted in descending order.

Sorting a vector in a particular order

The sort() function also accepts a compare function using which we can sort a vector in any particular order. Its syntax is given below,
Syntax

sort(myVector.begin(), myVector.end(), compare)

The compare function should have bool return type and has the following structure:

bool compare(argument1, argument2)
{
if(condition)
return true/false;

return true/false;

}

Now let us consider the program that sorts a vector of pairs on the basis of first element:

Source Code

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

// Create compare() function
bool compare(pair<int, int> &a, pair<int, int> &b)
{
// Compare on the basis of first value
if(a.first < b.first)
return true;
return false;
}

int main() {

// Create a vector of pairs
vector<pair<int,int>> myVector = {{10,20}, {30, 40}, {20,40}, {20,60}};

// Sort the vector
// on the basis of first value
sort(myVector.begin(), myVector.end(), compare);

// Print vector elements
cout << "myVector: { ";
for(auto it = myVector.begin() ; it != myVector.end() ; it++)
{
cout << '{' << it -> first << ',' << it -> second << '}' << " ";
}

cout << "}";

return 0;
}

write your code here: Coding Playground

Output

Output description

As you can see in the output, elements have been sorted on the basis of first element of pairs in the vector

Conclusion

In this article, we discussed how can sort a vector in C++. In the end we also illustrated how we can sort a vector on the basis of a particular condition by passing a compare function to the sort() function. We believe that this article has surely helped you to enhance your knowledge.