4-28打卡c++ string容器

#include<iostream>
#include<string>
using namespace std;
//assign
void test01()
{
    string str1;
    //截取三个字符
    str1.assign("hello,world", 3);
    //从第三个字符开始截取4个字符
    str1.assign("hello,world", 3, 4);
    cout << str1;
    cout << endl;
    //同理append也是如此
    cout << str1.append("hello,world", 5) << endl;
    cout << str1.append("hello,world", 4, 5);
}
//repalce find rfind
void test02()
{
    string str1 = "hello";
    //从第一个字符开始替换两个字符，同时插入一个字符串
    str1.replace(1, 2, "22222");
    cout << str1 << endl;
    str1 = "hello,world";
    //返回元素下标位置，找不到返回-1
    int pos = str1.find("l");
    cout << "pos=" << pos << endl;
    pos = str1.rfind('l');
    cout << "pos=" << pos << endl;
    cout << str1.rfind("wo");
}
//compare,insert size []
void test03()
{
    //compare比较字符串的ASCII值之和相等返回0，大于返回1，小于返回-1
    string str1 = "hello";
    string str2 = "hello";
    int res = str1.compare(str2);
    cout << res << endl;
    //insert插入,从下表为4的元素前插入
    str1.insert(4, "5555");
    cout << str1 << endl;
    //size返回字符串元素个数 []取出str1中的元素
    for (int i = 0; i < str1.size(); i++)
    {
        cout << str1[i];
    }
    cout << endl;
    
}
//erase substr
void test04()
{
    string str1 = "hello,world";
    //从下标为5的元素开始删除n个元素
    str1.erase(5, 2);
    cout << str1 << endl;
    string str2=str1.substr(0, 5);
    //从下标为0的元素开始返回5个字符
    cout << str2 << endl;
}

int main()
{
    /*test01();*/
    /*test02();*/
    /*test03();*/
    test04();
    return 0;
}