count
功能描述：
- 统计元素个数,返回一个整形变量
函数原型：
-
count(iterator beg, iterator end, value);// 统计元素出现次数
// beg 开始迭代器
// end 结束迭代器
// value 统计的元素
底层对比方法：
#include<iostream>
using namespace std;
#include<algorithm>
#include<functional>
#include<vector>
#include<string>
// 遍历函数
void Myprint1(int n) {
cout << n << " ";
}
// 查找内置数据类型
void test01() {
vector<int> v1;
v1.push_back(10);
v1.push_back(201);
v1.push_back(3);
v1.push_back(6);
v1.push_back(58);
v1.push_back(79);
v1.push_back(6);
v1.push_back(6);
v1.push_back(6);
cout << "针对内置数据类型" << endl;
cout << "容器v1里的元素如下：" << endl;
for_each(v1.begin(), v1.end(), Myprint1);
cout << endl << endl;
// 统计元素6出现的次数
int num1 = count(v1.begin(), v1.end(), 6);
if (num1 == 0) {
cout << "容器v1里没有6这个元素！" << endl << endl;
}
else
{
cout << "容器v1里6出现" << num1 <<"次"<< endl << endl;
}
cout << endl << endl;
// 统计元素8出现的次数
int num2 = count(v1.begin(), v1.end(), 8);
if (num2 == 0) {
cout << "容器v1里没有8这个元素！" << endl << endl;
}
else
{
cout << "容器v1里8出现" << num2 << "次" << endl << endl;
}
cout << endl << endl;
}
// 查找自定义数据类型
class Person {
public:
Person(string name, int age) :m_Age(age), m_Name(name) {}
int m_Age;
string m_Name;
// 重载==
// 不然怎么比较两个对象是否相等呢
bool operator==(const Person& p)
{
if (this->m_Name == p.m_Name && this->m_Age == p.m_Age)
{
return true;
}
return false;
}
};
void Myprint2(Person p) {
cout << "姓名：" << p.m_Name << " "
<< "年龄：" << p.m_Age << endl;
}
void test02() {
cout << "针对自定义数据类型" << endl;
vector<Person> v2;
//创建数据
Person p1("aaa", 10);
Person p2("bbb", 20);
Person p3("ccc", 30);
Person p4("ddd", 40);
Person p5("fff", 50);
Person p6("ggg", 60);
v2.push_back(p1);
v2.push_back(p2);
v2.push_back(p3);
v2.push_back(p4);
v2.push_back(p3);
v2.push_back(p3);
v2.push_back(p3);
v2.push_back(p3);
v2.push_back(p3);
v2.push_back(p3); v2.push_back(p3); v2.push_back(p3);
v2.push_back(p3);
cout << "容器v2里的元素如下:" << endl;
for_each(v2.begin(), v2.end(), Myprint2); cout << endl << endl;
int num2 = count(v2.begin(), v2.end(), p3);
if (num2 == 0) {
cout << "容器v2里没有p3这个对象！" << endl << endl;
}
else
{
cout << "容器v2里p3出现" << num2 << "次" << endl;
cout << "p3的姓名为：" << p3.m_Name << " "
<< "p3的年龄为：" << p3.m_Age << endl << endl;
}
cout << endl << endl;
int num3 = count(v2.begin(), v2.end(), p6);
if (num3 == 0) {
cout << "容器v2里没有p6这个对象！" << endl << endl;
}
else
{
cout << "容器v2里p6出现" << num2 << "次" << endl;
cout << "p6的姓名为：" << p3.m_Name << " "
<< "p6的年龄为：" << p3.m_Age << endl << endl;
}
cout << endl << endl;
}
int main() {
test01();
test02();
return 0;
}
总结： 统计自定义数据类型时候，需要配合重载 operator==
2.2.6 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。在什么情况下才统计元素个数
#include<iostream>
using namespace std;
#include<vector>
#include<algorithm>
void Myprint1(int n) {
cout << n << " ";
}
bool Mycompare1(int a, int b) {
return a > b;
}
void test01()
{
cout << "针对内置数据类型" << endl;
vector<int> v1;
v1.push_back(10);
v1.push_back(201);
v1.push_back(3);
v1.push_back(6);
v1.push_back(58);
v1.push_back(79);
v1.push_back(6);
v1.push_back(6);
v1.push_back(6);
cout << "v1里的元素如下：" << endl;
for_each(v1.begin(), v1.end(), Myprint1); cout << endl << endl;
reverse(v1.begin(), v1.end());
cout << "v1反转后，v1里的元素如下：" << endl;
for_each(v1.begin(), v1.end(), Myprint1); cout << endl << endl;
}
// 针对自定义数据类型
class Person {
public:
Person(string name, int age) :m_Name(name), m_Age(age) {
}
int m_Age;
string m_Name;
};
class Mycompare2 {
public:
bool operator()(Person p1, Person p2) {
return p1.m_Age < p2.m_Age;
}
};
class Mycompare3 {
public:
bool operator()(Person p1,Person p2) {
return p1.m_Age=p2.m_Age;
}
};
void Myprint2(Person p) {
cout << "姓名：" << p.m_Name << " "
<< "年龄：" << p.m_Age << endl;
}
void test02() {
cout << "针对自定义数据类型" << endl;
vector<Person> v2;
//创建数据
Person p1("aaa", 10);
Person p2("bbb", 5);
Person p3("ccc", 60);
Person p4("ddd", 30);
Person p5("fff", 3);
Person p6("fff", 200);
Person p7("fff", 105);
v2.push_back(p1);
v2.push_back(p2);
v2.push_back(p3);
v2.push_back(p4);
v2.push_back(p5);
v2.push_back(p6);
v2.push_back(p7);
cout << "v2里的元素如下：" << endl;
for_each(v2.begin(), v2.end(), Myprint2); cout << endl << endl;
reverse(v2.begin(), v2.end());
cout << "v2反转后，里面的元素如下：" << endl;
for_each(v2.begin(), v2.end(), Myprint2); cout << endl << endl;
}
int main() {
test01();
cout << endl << endl << endl;
test02();
cout << endl << endl << endl;
system("pause");
return 0;
}
