count_if按条件统计元素个数

#include<iostream>
using namespace std;
#include<deque>
#include<algorithm>
#include<string>
bool a(int val)
{
	return val % 2 == 0;
}
void test01()
{
	deque<int> d;
	d.push_front(6);
	d.push_front(5);
	d.push_front(4);
	d.push_front(3);
	d.push_front(2);
	d.push_front(1);
	cout << count_if(d.begin(), d.end(), a) << endl;
}
int main()
{
	test01();
	system("pause");
	return 0;
}

#include<iostream>
using namespace std;
#include<deque>
#include<algorithm>
#include<string>
class person {
public:
	string name;
	int age;
	person(string n, int a) :name(n), age(a) {}
};
//仿函数
class compare {
public:
 //const可写可不写，最好写上
	bool operator()(const person &p)
	{
		return p.age > 40;
	}
};
void test01()
{
	//count_if
	person p1("孙悟空", 180);
	person p2("沙僧", 60);
	person p3("猪八戒", 80);
	person p4("白骨精", 18);
	person p5("牛魔王", 40);
	deque<person> m = { p1,p2,p3,p4,p5 };
	person p6("二郎神", 30);
	cout << count_if(m.begin(), m.end(), compare());
}
int main()
{
	test01();
	system("pause");
	return 0;
}