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C++：string 1

backend 2025/5/9 8:20:30

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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