#include <bits/stdc++.h>

using namespace std;

int main() {
    printf("hello world\n");
    //两种方式是等价
    cout << "a" << 1 << "b" << endl;
    printf("%s%d%s\n","a",1,"b");

    //将数字转为字符串
    ostringstream stream;
    stream << 1; //n为要转字符串的整数
    string s = stream.str();
    printf("a%sb\n", s.c_str());
    //转义
    printf("%s","%s");
    return 0;
}