Description : : Returns the number of elements in the range [first, last) satisfying specific criteria(counts the elements that are equal to value).
Example :
std::vector<int> v{ 1, 2, 3, 4, 4, 3, 7, 8, 9, 10 };
// determine how many integers in a std::vector match a target value.
int target1 = 3;
int num_items1 = std::count(v.begin(), v.end(), target1);
std::cout << "number: " << target1 << " count: " << num_items1 << '\n';