C++ algorithm count_if() function
Example
Count how many times a number greater than 5 appears in a vector:
bool greater_than_5(int value) {
return value > 5;
}
int main() {
vector<int> numbers = {1, 7, 3, 5, 9, 2};
int amount = count_if(numbers.begin(), numbers.end(), greater_than_5);
cout << "There are " << amount << " values greater than 5.";
return 0;
}Definition and Usage
The count_if() function tests each element in a data range and counts the number of elements that match a specified condition.
The range of data is specified by iterators.
The condition is specified by a function that takes the value of an element as an argument and returns a boolean value which is 1 if the condition is matched and 0 if the condition is not matched.
Syntax
count_if(iterator start, iterator end, function condition);Parameter Values
| Parameter | Description |
|---|---|
| start | Required. An iterator pointing to the start of the data range being test. |
| end | Required. An iterator pointing to the end of the data range being test. Elements up to this position will be test, but the element at this position will not be included. |
| condition | Required. A function that takes the value of an element in the data range as an argument and returns a boolean value. |
Technical Details
| Returns: | An integer representing the number of elements in the data range that matched the condition. |
|---|
Related Pages
Read more about data structures in our Data Structures Tutorial.
Read more about iterators in our Iterators Tutorial.
Read more about algorithms in our Algorithms Tutorial.
Read more about booleans in our Booleans Tutorial.
