练习题：
这个题的思路是从前往后，从后往前同时找，不是字母的话就继续，是的话就交换。
代码：
#define _CRT_SECURE_NO_WARNINGS 1
#include <iostream>
#include <string>
using namespace std;
//1、4个默认成员函数
void test_string1()
{
string s1;
string s2("hello");
string s3("hello", 2);
string s4(s2);
string s5(s2, 1, 2);
string s6(s2, 1);
string s7(10, 'a');
s1 = s7;
cout << s1 << endl;
cout << s2 << endl;
cout << s3 << endl;
cout << s4 << endl;
cout << s5 << endl;
cout << s6 << endl;
cout << s7 << endl;
}
//遍历
void test_string2()
{
string s1("hello");
s1 += ' ';
s1 += "world";
cout << s1 << endl;
//读 推荐用这种方式
for (size_t i = 0; i < s1.size(); i++)
{
cout << s1[i] << " ";
}
//写
for (size_t i = 0; i < s1.size(); i++)
{
s1[i] += 1;
}
cout << endl;
//读
for (size_t i = 0; i < s1.size(); i++)
{
cout << s1[i] << " ";
}
cout << endl;
//迭代器
//写
string::iterator it = s1.begin();
while (it != s1.end())
{
*it -= 1;
++it;
}
//读
it = s1.begin();
while (it != s1.end())
{
cout << *it << " ";
++it;
}
cout << endl;
//范围for
//C++11 -> 原理是被替换成迭代器
for (auto ch : s1)
{
cout << ch << " ";
}
cout << endl;
}
int string2int(const string& str)
{
int val = 0;
string::const_iterator it = str.begin();
while (it != str.end())
{
//*it = 'a';//const 迭代器不能修改
val *= 10;
val += *it-'0';
++it;
}
return val;
}
void test_string3()
{
string s1("hello world!");
//倒着往前遍历
string::reverse_iterator rit = s1.rbegin();
//读
while (rit != s1.rend())
{
cout << *rit << " ";
++rit;
}
cout << endl;
string nums("12345");
cout << string2int(nums) << endl;
//方向：正向和反向
//属性：普通和const
}
void test_string4()
{
string s1("hello world!");
string s2("hello");
cout << s1.size() << endl;
cout << s2.size() << endl;
cout << s1.length() << endl;
cout << s2.length() << endl;
cout << s1.capacity() << endl;
cout << s2.capacity() << endl;
s1 += "hehe";
cout << s1.capacity() << endl;
s1.clear();//只是清除了内容，并不将capacity置0
cout << s1 << endl;
cout << s1.capacity() << endl;
}
void test_string5()
{
string s;
//s.reserve(100);
//s.resize(100, 'x');
size_t sz = s.size();
cout << "making s grow:\n";
for (int i = 0; i < 100; i++)
{
s.push_back('c');
if (sz != s.capacity())
{
sz = s.capacity();
cout << "capacity changed:" << sz << endl;
}
}
}
void test_string6()
{
//string s;
//s.push_back('x');
//s.append("x");
//s += '1';
//s += "hello";
//cout << s << endl;
string s;
s += '1';
s += "3456";
cout << s << endl;
s.insert(s.begin(), '0');
cout << s << endl;
s.insert(2, "2");
cout << s << endl;
s.erase(2, 3);
cout << s << endl;
s.erase(2, 10);
cout << s << endl;
}
int main()
{
//test_string1();
//test_string2();
//test_string3();
//test_string4();
//test_string5();
test_string6();
return 0;
}
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