【原】比较string对象及其+操作 79

#include<iostream>

using namespace std;

#include<string>

int main()

{

 //string 的empty和size操作

string s1;

if (s1.empty())

{

cout << "空的" << endl;//空的

}

else

{

cout << "不是空的" << endl;

}

string s2("12345");

cout << "s2的位数：" << s2.size() << endl; //s2的位数：5

auto a = s2.size();//a=5;,a.size()返回的是无符号数，

int b = -10;

if (a > b)//int 和 无符号 相比较，int 转换为无符号

{

cout << "a>b" << endl;

}

else

{

cout<< "a<b" << endl;

}

//  a<b

//sring的==  >  <

//string 的+

string a1 = "aga";

string a2 = "agrq";

string a3 = a1 + a2;

cout << "a3: " << endl;

string a4 = "sagrwa" + a3;

cout << "a4:" << a3 << endl;

//string a5 = "sgws" + "sgwgger";//报错 string +,左右必有一个string,不能全是字面值

system("pause");

}