C++: What is the difference between std::count and std::count_if?

1std::vector<int> v = {1, 2, 2, 3, 2, 4};
2int c = std::count(v.begin(), v.end(), 2);
3// c = 3

1// Count even numbers
2int c = std::count_if(v.begin(), v.end(),
3    [](int x) { return x % 2 == 0; }
4);
5// c = 4 (2, 2, 2, 4)