C++count_if
功能描述:
按条件统计元素个数
函数原型:
count_if(iterator beg, iterator end, _Pred);
//按条件统计元素出现次数
//beg开始迭代器
//end结束迭代器
//_Pred谓词
代码示例:
#include<iostream>
#include<string>
#include<algorithm>
#include<vector>
using namespace std;
//常用查找算法 count_if
class Greater20
{
public:
bool operator()(int val)
{
return val > 20;
}
};
//统计内置数据类型
void test01()
{
vector<int>v;
v.push_back(10);
v.push_back(40);
v.push_back(30);
v.push_back(20);
v.push_back(40);
v.push_back(20);
int num= count_if(v.begin(), v.end(), Greater20());
cout << "大于20的元素个数为:" <<num<< endl;
}
class Person
{
public:
Person(string name,int age)
{
this->m_Name = name;
this->m_Age = age;
}
string m_Name;
int m_Age;
};
class AgeGreater20
{
public:
bool operator()(const Person &p)
{
return p.m_Age > 20;
}
};
void test02()
{
vector<Person>v;
Person p1("刘备", 35);
Person p2("关羽", 35);
Person p3("张飞", 35);
Person p4("赵云", 40);
Person p5("曹操", 20);
v.push_back(p1);
v.push_back(p2);
v.push_back(p3);
v.push_back(p4);
v.push_back(p5);
//统计 大于
int num= count_if(v.begin(), v.end(), AgeGreater20());
cout << "大于20岁的人员个数为:" << num << endl;
}
int main()
{
test01();
test02();
system("pause");
return 0;
}
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C++count_if
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