#include<bits/stdc++.h>
using namespace std;
int main() {
	string s;
	cin >> s;
	cout << s << endl;
	cout << s.size() << endl;//4
	cout << s[0] << endl;//'e'
	return 0;
}

#include<bits/stdc++.h>
using namespace std;
int main() {
	int n;
	cin >> n;
	string s;
	getchar();
	getline(cin,s);
	cout << n << endl;
	cout << s << endl;
	return 0;
}

查找find函数

#include<bits/stdc++.h>
using namespace std;
int main() {
	string s="hello world";
	if(s.find("llo") != string::npos){
		cout << "Yes";
		cout << s.find("llo")<<endl;;// 找到的下标 
	}else{
		cout << "No";
	}
	int k = s.find("lolo");
	cout << k << endl;//k:-1;
	if(k!=-1){
		cout << k << endl;
	}
	
	s="hello world";
	k = s.find("llo",3);//从下标3开始找"llo" 
	
	s="abcabababc";
	k = s.rfind("ab");//k:7,从右边找到左边 
	return 0;
}

插入insert

#include<bits/stdc++.h>
using namespace std;
int main() {
	string s="hello world";
	s.insert(3,"abc");//在下标3前面插入"abc" 
	cout << s << endl;
	
	s="hello world";
	s = s+"abc";
	cout << s << endl; //hello worldabc
	
	s = "abc"+"efg";//错误： 两个字符串常量不能相加 
	return 0;
}

删除erase

#include<bits/stdc++.h>
using namespace std;
int main() {
	string s="hello world";
	s.erase(2,3);//从下标2开始删除3个字符 
	cout << s << endl; // he world
	return 0;
}

更换更改replace

#include<bits/stdc++.h>
using namespace std;
int main() {
	string s=;
	s.replace(1,4,"i") ;//从下标1开始的后面4个字符修改成"i" 
	cout << s << endl;//"hi world"
	return 0;
}

截取substr

#include<bits/stdc++.h>
using namespace std;
int main() {
	string s="hello world";
	string ts;
	ts = s.substr(2,6);//从下标2开始截取6字符（llo wo） 
	cout << s << endl; // hello world
	cout << ts << endl;// llo wo
	return 0;
}