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count() in C++ STL - GeeksforGeeks

Last Updated : 27 Nov, 2024

In C++, the count() is a built-in function used to find the number of occurrences of an element in the given range. This range can be any STL container or an array. In this article, we will learn about the count() function in C++.

Let’s take a quick look at a simple example that uses count() method:

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

int main() {
    vector<int> v = {2, 3, 2, 1, 5, 4, 2};

    // Count the occurrence of 2
    cout << count(v.begin(), v.end(), 2);
    return 0;
}

This article covers the syntax, usage, and common examples of count() function in C++:

The count() function is defined inside the <algorithm> header file.

count(first, last, val);

• first: Iterator to the first element of the range.
• last: Iterator to the element just after the last element of the range.
• val: Value to be counted.

• If the value found, it returns the number of its occurrences.
• Otherwise, it returns 0.

The following examples demonstrates the use of count() function for different purposes:

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

int main() {
    vector<string> v = {"Hi", "Geeks", 
                        "GeeksforGeeks", 
                        "Geeks"};

    // Count the occurrence of "Geeks"
    cout << count(v.begin(), v.end(), "Geeks");
  
    return 0;
}

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

int main() {
    multiset<int> m= {1, 1, 2, 3, 2, 2, 2, 1};
	
    // Counting the frequency of 2 
    cout << count(m.begin(), m.end(), 2);
  
    return 0;
}

Note: Unique value containers such as set, maps, etc. can only return either 1 or 0 from the count function.

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

int main() {
    vector<int> v = {2, 3, 2, 1, 5, 4, 2};
  	int val = 7;
  
  	// Count the occurrence of 7
  	int c = count(v.begin(), v.end(), val);

    // Check if the element exists
    if (c)
      	cout << c;
    else
      	cout << val << " Not Exists";
  
    return 0;
}

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