Essential C++学习笔记及源代码(第1章 C++编程基础)

第1章是本书的基本知识和入门重点。
本章介绍了C++的基础编程知识，其中包括：
1、一些基础数据类型：布尔型(bool)、字符型(char)、整型(int)以及浮点型(float和double)。
2、算术运算符、关系运算符以及逻辑运算符，用以操作上述基础数据类型。这些运算符包括加(+)、减(-)、乘(*)、除(/)、相等运算符(==)、小于等于运算符(<=)以及赋值运算符(=)，也包含比较特殊的递增运算符(++)、条件运算符(?:)以及复合赋值运算符例如+=等。
3、条件分支以及循环控制语句，if和while循环可用来改变程序的控制流程。
4、一些复合数据类型，例如指针以及数组。指针可以让我们间接使用一个已存在的对象，数组则用来定义一组具有相同数据类型的元素。
5、一套标准的、通用的抽象化库，例如字符串(string)以及向量(vector)。
作者使用了一个小程序帮助读者们很好地掌握C++的基础知识，笔者在此处归纳总结并进行分析，再附上课后编程练习解答使得更好地掌握已学知识，注意建立工程文件后再运行小程序，若是对您有用的话请点赞或分享提供给它人。

//ch1_main.cpp

#include <iostream>
#include <string>
#include "ch1.h"
using namespace std;int main()
{user_profile up; //声明一个玩家对象;if (greet_user(&up)) //问候玩家并选择是否开始游戏;{play_game(&up);          //游戏主菜单;display_statistics(&up); //显示玩家猜测次数和猜测正确率;}return 0;
}

//-----------------------------------------------------------;

//-----------------------------------------------------------;
//ch1.cpp

#include "ch1.h"pvec Fibonacci_gen_elems(int pos) //生成一个Fibonacci数列;
{static vector<unsigned> _elems;if (!check_integrity(pos)){return 0;}if (_elems.empty()){_elems.push_back(1);_elems.push_back(1);}if (_elems.size() < pos){int ix = _elems.size();int n_2 = _elems[ix - 2];int n_1 = _elems[ix - 1];for (int elem; ix < pos; ++ix){elem = n_2 + n_1;_elems.push_back(elem);n_2 = n_1;n_1 = elem;}}return &_elems;
}pvec Pell_gen_elems(int pos) //生成一个Pell数列;
{static vector<unsigned> _elems;if (!check_integrity(pos)){return 0;}if (_elems.empty()){_elems.push_back(1);_elems.push_back(2);}if (_elems.size() < pos){int ix = _elems.size();int n_2 = _elems[ix - 2];int n_1 = _elems[ix - 1];for (int elem; ix < pos; ++ix){elem = n_2 + 2 * n_1;_elems.push_back(elem);n_2 = n_1;n_1 = elem;}}return &_elems;
}pvec Lucas_gen_elems(int pos) //生成一个Lucas数列;
{static vector<unsigned> _elems;if (!check_integrity(pos)){return 0;}if (_elems.empty()){_elems.push_back(1);_elems.push_back(3);}if (_elems.size() < pos){int ix = _elems.size();int n_2 = _elems[ix - 2];int n_1 = _elems[ix - 1];for (int elem; ix < pos; ++ix){elem = n_2 + n_1;_elems.push_back(elem);n_2 = n_1;n_1 = elem;}}return &_elems;
}pvec Triangular_gen_elems(int pos) //生成一个Triangular数列;
{static vector<unsigned> _elems;if (!check_integrity(pos)){return 0;}if (_elems.size() < pos){int ix = _elems.size() ? _elems.size() + 1 : 1;for (; ix <= pos; ++ix){_elems.push_back(ix * (ix + 1) / 2);}}return &_elems;
}pvec Square_gen_elems(int pos) //生成一个Square数列;
{static vector<unsigned> _elems;if (!check_integrity(pos)){return 0;}if (_elems.size() < pos){int ix = _elems.size() ? _elems.size() + 1 : 1;for (; ix <= pos; ++ix){_elems.push_back(ix * ix);}}return &_elems;
}pvec Pentagonal_gen_elems(int pos) //生成一个Pentagonal数列;
{static vector<unsigned> _elems;if (!check_integrity(pos)){return 0;}if (_elems.size() < pos){int ix = _elems.size() ? _elems.size() + 1 : 1;for (; ix <= pos; ++ix){_elems.push_back(ix * (3 * ix - 1) / 2);}}return &_elems;
}//使用一个函数指针数组来访问在每个函数中产生的静态数列;
pfunc gen_elems[] =
{0,Fibonacci_gen_elems,Pell_gen_elems,Lucas_gen_elems,Triangular_gen_elems,Square_gen_elems,Pentagonal_gen_elems
};//生成数列的种类;
const char *name_seq[] =
{"Invalid Sequence","Fibonacci", "Pell", "Lucas","Triangular", "Square", "Pentagonal"
};//游戏等级;
int level_size[] = {8, 8, 32, 128, 512};//一些反馈信息;
const char *wrong_msg[] =
{"Oops! Nice guess but not quite it.","Hmm. Sorry. Wrong again.","Ah, this is harder than it looks, isn't it?","It must be getting pretty frustrating by now!"
};//显示玩家在游戏中的猜测信息;
void display_statistics(user_profile *puser)
{cout << "Game Statistics for " << puser->name << "\n\t";cout << "# guesses: " << puser->guesses << "\n\t";cout << "# correct: " << puser->correct << "\n\t";cout << "% correct: ";cout << (static_cast<float>(puser->correct) / static_cast<float>(puser->guesses)) * 100 << endl;return;
}//初始化玩家信息和游戏信息;
bool greet_user(user_profile *puser)
{cout << "Hi. What's your name? ";string nm;cin >> nm;if (nm.empty() || nm[0] == ' '){cout << "ok. I guess you don't want to play. See ya!\n";return false;}cout << "Hi, " << nm;cout << " Would you like to play Guess the Sequence? (y/n) ";char ch;cin >> ch;if (ch != 'y' && ch != 'Y'){cout << "ok. I'm sorry you don't want to play.\n";return false;}cout << "\n\n";cout << "Hey, that's great, " << nm << ".\n";cout << "We'll start in just a moment.\nIt\'s simple, really!\n";cout << "I will print out two elements of a sequence\n";cout << "You just answer with the element value that comes next!\n\n";cout << "Oh, by the way, do you consider yourself a\n\t";cout << "beginner     -- enter 1\n\t";cout << "intermediate -- enter 2\n\t";cout << "advanced     -- enter 3\n\t";cout << "guru         -- enter 4\n\t" << endl;int level;cin >> level;if (level < 1 || level > 4){level = 4;}init_user(puser, nm, level); //初始化游戏各项信息;return true;
}//打印当前数列中的所有元素;
void print_seq(user_profile *puser)
{for (int i = 0; i < puser->cur_seq_vec->size(); ++i){cout << (*puser->cur_seq_vec)[i] << ' ';}cout << endl;return;
}void display_seq(user_profile *puser)
{pvec p = seq_vec(puser);cout << "The first two elements of the series are: ";cout << (*p)[puser->pos - 3] << ", " << (*p)[puser->pos - 2]; //显示倒数第3个和倒数第2个数;cout << "\nWhat is the next element? ";return;
}void set_up_index(user_profile *puser)
{static string wherefrom("set_up_index");//在数列等级数组中随机获取一个位置;puser->pos = rand() % (level_size[puser->level]);if (puser->pos < 3) //显示数列最后3个数, 位置不对的话就加3防止出错;{puser->pos += 3;}set_seq_vec(puser, (*gen_elems[puser->cur_seq])(puser->pos));trace(wherefrom, "new position: ", puser->pos);return;
}void reset_seq(user_profile *puser)
{static string wherefrom("reset_seq");int new_seq = gen_seq_id(puser->level); //设置游戏猜测序列的种类;if (new_seq == puser->cur_seq){new_seq = new_seq < ns_cnt ? new_seq + 1 : 1;}puser->cur_seq = static_cast<num_sequence>(new_seq); //设置玩家当前猜测序列的种类;set_up_index(puser);print_seq(puser);trace(wherefrom, "new sequence: ", name_seq[puser->cur_seq]);return;
}void init_user(user_profile *puser, const string &nm, int level)
{static string wherefrom("init_user");puser->name = nm;puser->guesses = 0;puser->correct = 0;puser->level = level;reset_seq(puser);                            //设置游戏参数;trace(wherefrom, nm, puser->cur_seq, level); //打印追踪信息;return;
}bool correct_guess(user_profile *puser, int guess)
{pvec p = seq_vec(puser);if (guess == (*p)[puser->pos - 1]){return true;}return false;
}void play_game(user_profile *puser)
{bool next_seq = true;bool go_for_it = true;bool got_it = false;int num_tries;while (next_seq == true){num_tries = 0;display_seq(puser);while ((got_it == false) && (go_for_it == true)){unsigned int usr_guess;cin >> usr_guess;if (correct_guess(puser, usr_guess)) //玩家猜对了;{bump_correct(puser);got_it = true;cout << "Hey, most excellent! \n\t";cout << usr_guess << " is element # ";cout << puser->pos << " of the ";cout << name_seq[puser->cur_seq] << " sequence.\n"; //打印当前数列的部分信息;}else{bump_guess(puser);cout << wrong_msg[num_tries < ns_wrong_msg ? num_tries : ns_wrong_msg - 1]; //打印一条反馈信息;cout << " Would you like to try again? (y/n) ";char usr_rsp;cin >> usr_rsp;if (usr_rsp == 'N' || usr_rsp == 'n'){go_for_it = false;}else{++num_tries;cout << "Your next guess? ";}}}cout << "Want to try another sequence? (y/n) ";char try_again;cin >> try_again;if (try_again == 'N' || try_again == 'n'){next_seq = false;}else{got_it = false;reset_seq(puser); //再次尝试游戏则重置游戏信息;}}return;
}

//-----------------------------------------------------------;

//-----------------------------------------------------------;
//ch1.h

#ifndef CH1_H_
#define CH1_H_
#include <iostream>
#include <vector>
#include <string>
#include <cstdlib>
using namespace std;typedef const vector<unsigned> *(*pfunc)(int); //声明一个函数指针指向返回值为const vector<unsigned> *参数列表为int的函数;
typedef const vector<unsigned> *pvec;          //声明一个指向const vector<unsigned>对象的指针;enum num_sequence //定义一些元素序列的值;
{ns_unk,ns_fib,ns_pell,ns_lucas,ns_tri,ns_sq,ns_pent,ns_cnt = 6,ns_wrong_msg = 4
};struct user_profile
{string name;          //玩家名字;int guesses;          //玩家猜测次数;int correct;          //玩家猜测正确次数;int level;            //玩家游戏等级;num_sequence cur_seq; //玩家猜测数列的类型;pvec cur_seq_vec;     //存储玩家当前猜测数列的元素;int pos;              //存储玩家当前猜测数列的随机一个元素位置;
};extern pfunc gen_elems[];
extern const char *name_seq[];
extern const char *wrong_msg[];
extern int level_size[];extern bool greet_user(user_profile *);
extern void play_game(user_profile *);
extern void display_statistics(user_profile *);extern pvec Fibonacci_gen_elems(int);
extern pvec Pell_gen_elems(int);
extern pvec Lucas_gen_elems(int);
extern pvec Triangular_gen_elems(int);
extern pvec Square_gen_elems(int);
extern pvec Pentagonal_gen_elems(int);extern void set_seq(user_profile *, int);
extern const char *seq_id(user_profile *);
extern void init_user(user_profile *puser, const string &nm, int level);
extern bool correct_guess(user_profile *puser, int guess);inline void set_seq_vec(user_profile *pu, pvec p) { pu->cur_seq_vec = p; } //设置玩家当前所猜数列, 赋予一个新数列;
inline pvec seq_vec(user_profile *pu) { return pu->cur_seq_vec; }          //获取玩家当前所猜数列的地址;inline string
user_name(user_profile *puser)
{return puser->name; //获取玩家名字;
}inline num_sequence
seq(user_profile *puser)
{return puser->cur_seq; //获取玩家当前猜测的数列类型;
}inline void
bump_guess(user_profile *puser)
{++puser->guesses; //递增猜测次数;
}inline void
bump_correct(user_profile *puser)
{bump_guess(puser);++puser->correct; //递增猜测次数和猜测正确次数;
}inline num_sequence
gen_seq_id(unsigned ui)
{srand(ui++);return static_cast<num_sequence>((rand() % ns_cnt) + 1); //随机选择一个数列进行游戏猜测;
}/*重载打印追踪信息的一系列函数显示当前游戏情况;
*/
inline void trace(const string &where, const string &msg, const string &data)
{cerr << where << " " << msg << " " << data << endl;
}inline void trace(const string &where, const string &msg, int val)
{cerr << where << " " << msg << " " << val << endl;
}inline void trace(const string &where, const string &msg, int val, int val2)
{cerr << where << " " << msg << " " << val << ' ' << val2 << endl;
}inline void trace(const string &where, int val1, int val2)
{cerr << where << " " << val1 << " " << val2 << endl;
}inline bool
check_integrity(int pos) //检查元素索引是否正确;
{const int max_elems = 512;if (pos <= 0 || pos > max_elems){cerr << "!! invalid position: " << pos;cerr << " Cannot honor request\n";return false;}return true;
}inline num_sequence check_sequence(int id) //检查数列索引是否正确;
{if (id <= 0 || id > ns_cnt){cerr << "!! invalid sequence value: " << id;cerr << " Choosing one at random\n";id = (id % ns_cnt) + 1;}return static_cast<num_sequence>(id);
}#endif

//-----------------------------------------------------------;

//-----------------------------------------------------------;
//Practise1.1.cpp

#include <iostream>
#include <string>
using namespace std;int main()
{string user_name;cout << "Please enter your first name: ";cin >> user_name;cout << "\nHello, " << user_name << " ... and goodbye!\n";return 0;
}

//-----------------------------------------------------------;

Practise1.2中注释掉#include <string>导致程序未找到对象string产生错误；注释掉using namespace std;后程序找不到所有包含在命名空间std中的类，产生错误。

Practise1.3中将main改为my_main后操作系统找不到程序的入口点main函数产生错误，因为一个C++程序必定要有一个main函数。

//-----------------------------------------------------------;
//Practise1.4.cpp

#include <iostream>
#include <string>
using namespace std;int main()
{string firstname, lastname;cout << "Please enter your first name and last name: ";cin >> firstname >> lastname;cout << "\nHello, " << firstname << " " << lastname << " ... and goodbye!\n";return 0;
}

//-----------------------------------------------------------;

//-----------------------------------------------------------;
//Practise1.5.cpp

#include <iostream>
#include <cstring>
#include <string>
#include <iomanip>
using namespace std;void solve_by_string()
{string user_name;cout << "Please enter your name: ";cin >> user_name;switch (user_name.size()){case 0:{cout << "Ah, the user with no name. ";cout << "Well, ok, hi, user with no name\n";break;}case 1:{cout << "A 1-character name? Hmm, have you read Kafka?: ";cout << "hello, " << user_name << endl;break;}default:{cout << "Hello, " << user_name;cout << " -- happy to make your acquaintance!\n";break;}}return;
}void solve_by_cstyle()
{const int maxn = 128;char user_name[maxn];cout << "Please enter your name: ";cin >> setw(maxn) >> user_name; //限制输入的字符数目;switch (strlen(user_name)){case maxn - 1:{cout << "That is a very big name, indeed -- ";cout << "we may have needed to shorten it!\n";cout << "In any case,\n";}default:{cout << "Hello, " << user_name;cout << " -- happy to make your acquaintance!\n";break;}}return;
}int main()
{cout << "Output contents by string" << endl;solve_by_string();cout << "Output contents by cstyle" << endl;solve_by_cstyle();return 0;
}

//-----------------------------------------------------------;

//-----------------------------------------------------------;
//Practise1.6.cpp

#include <iostream>
#include <vector>
using namespace std;void solve_by_vector()
{int i, t, n;int sum = 0;vector<int> vt;cout << "Please enter a number for number of elements: ";cin >> n;cout << "Enter " << n << " numbers:" << endl;for (i = 0; i < n; ++i){cin >> t;vt.push_back(t);}for (i = 0; i < vt.size(); ++i){sum += vt[i];}cout << "Sum of " << n << " elements: " << sum;cout << ". Average: " << static_cast<double>(sum) / n << "(Vector)\n";return;
}void solve_by_array()
{const int maxn = 100;int sum = 0;int i, n, a[maxn];cout << "Please enter a number for number of elements(0 < n <= 100): ";cin >> n;if (n <= 0 || n > 100){cout << "Uncorrect number! n will be assigned " << maxn << ".\n";n = maxn;}cout << "Enter " << n << " numbers:" << endl;for (i = 0; i < n; ++i){cin >> a[i];}for (i = 0; i < n; ++i){sum += a[i];}cout << "Sum of " << n << " elements: " << sum;cout << ". Average: " << static_cast<double>(sum) / n << "(Array)\n";return;
}int main()
{solve_by_vector();solve_by_array();return 0;
}

//-----------------------------------------------------------;

//-----------------------------------------------------------;
//Practise1.7.cpp

/*
在源文件Practise1.7.cpp所在目录下创建一个文本文件text.txt
内容如下:
we were her pride of ten she named us:
Phoenix, the Prodigal, Benjamin,
and perspicacious, pacific Suzanne.
*/#include <iostream>
#include <cstdlib>
#include <fstream>
#include <vector>
#include <string>
#include <algorithm>
using namespace std;int main()
{ifstream infile("text.txt");if (!infile){cout << "Don't exist words.txt!\n";exit(EXIT_FAILURE);}ofstream outfile("sorted_text.txt");if (!outfile){cout << "Don't exist sorted_words.txt!\n";exit(EXIT_FAILURE);}string word;vector<string> text;while (infile >> word){text.push_back(word);}cout << "Original text:\n";for (int i = 0; i < text.size(); ++i){cout << text[i] << ' ';}sort(text.begin(), text.end());cout << "\nSorted text:\n";for (int i = 0; i < text.size(); ++i){cout << text[i] << ' ';outfile << text[i] << ' ';}outfile << endl;return 0;
}

//-----------------------------------------------------------------

Practise1.8可以参考书上的P210和211页。

//--------------------2021年6月17日 -------------------------

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