2.1 关系运算符

==, !=
>, >=
<, <=

2.2 条件语句

02.score_rater.cpp

#include <iostream>
using namespace std;int main()
{if (true){cout << "This is always displayed.\n\n";}if (false)cout << "This is never displayed.\n\n";int score = 1000;if (score){cout << "At least you didn't score zero.\n\n";}if (score >= 250)cout << "You scored 250 or more. Decent.\n\n";if (score >= 500){cout << "You scored 500 or more. Nice.\n\n";if (score >= 1000)cout << "You scored 1000 or more. Impressive!\n";}return 0;
}

02.score_rater2.cpp

#include <iostream>
using namespace std;int main()
{int score;cout << "Enter your score: ";cin >> score;if (score >= 1000)cout << "You scored 1000 or more. Impressive!\n";elsecout << "You scored less than 1000.\n";return 0;
}

02.score_rater3.cpp

#include <iostream>
using namespace std;int main()
{int score;cout << "Enter your score: ";cin >> score;if (score >= 1000){cout << "You scored 1000 or more. Impressive!\n";}else if (score >= 500){cout << "You scored 500 or more. Nice.\n";}else if (score >= 250){cout << "You scored 250 or more. Decent.\n";}else{cout << "You scored less than 250. Nothing to brag about.\n";}return 0;
}

2.5 switch语句

只用于比较int型（或可当作int型处理的值，char型或枚举型）。

02.menu_chooser.cpp

#include <iostream>
using namespace std;int main()
{cout << "Difficulty Levels\n\n";cout << "1 - Easy\n";cout << "2 - Normal\n";cout << "3 - Hard\n\n";int choice;cout << "Choice: ";cin >> choice;switch (choice){default:cout << "You made an illegal choice.\n";break;case 1:cout << "You picked Easy.\n";break;case 2:cout << "You picked Normal.\n";break;case 3:cout << "You picked Hard.\n";break;}return 0;
}

2.6 while循环

02.play_again.cpp

#include <iostream>
using namespace std;int main()
{char again = 'y';while (again == 'y'){cout << "\n**Played an exciting game**";cout << "\nDo you want to play again? (y/n): ";cin >> again;}cout << "\nOkay, bye.";return 0;
}

2.7 do循环

02.play_again2.cpp

#include <iostream>
using namespace std;int main()
{char again;do{cout << "\n**Played an exciting game**";cout << "\nDo you want to play again? (y/n): ";cin >> again;} while (again == 'y');cout << "\nOkay, bye.";return 0;
}

2.8 break和continue语句

02.finicky_counter.cpp

#include <iostream>
using namespace std;int main()
{int count = 0;while (true){count += 1;// end loop if count is greater than 10if (count > 10){break;}// skip the number 5if (count == 5){continue;}cout << count << endl;}return 0;
}

2.9 逻辑运算符

!
&&
||
注意优先级和短路现象

02.designers_network.cpp

#include <iostream>
#include <string>
using namespace std;int main()
{string username;string password;bool success;cout << "\tGame Designer's Network\n";do{cout << "\nUsername: ";cin >> username;cout << "Password: ";cin >> password;if (username == "S.Meier" && password == "civilization"){cout << "\nHey, Sid.";success = true;}else if (username == "S.Miyamoto" && password == "mariobros"){cout << "\nWhat's up, Shigeru?";success = true;}else if (username == "W.Wright" && password == "thesims"){cout << "\nHow goes it, Will?";success = true;}else if (username == "guest" || password == "guest"){cout << "\nWelcome, guest.";success = true;}else{cout << "\nYour login failed.";success = false;}} while (!success);return 0;
}

2.10 随机数

02.die_roller.cpp

#include <iostream>
#include <cstdlib>
#include <ctime>
using namespace std;int main()
{srand(static_cast<unsigned int>(time(0))); // seed random number generator based on current timeint randomNumber = rand(); // generate random numberint die = (randomNumber % 6) + 1; // get a number between 1 and 6cout << "You rolled a " << die << endl;return 0;
}

2.12 Guess My Number游戏

02.guess_my_number.cpp

#include <iostream>
#include <cstdlib>
#include <ctime>
using namespace std;int main()
{srand(static_cast<unsigned int>(time(0))); // seed random number generatorint secretNumber = rand() % 100 + 1; // 生成随机数int tries = 0;int guess;cout << "\tWelcome to Guess My Number\n\n";do{cout << "Enter a guess: ";cin >> guess; // 获取用户猜测++tries;	  // 增加猜测次数// 告知猜测情况if (guess > secretNumber){cout << "Too high!\n\n";}else if (guess < secretNumber){cout << "Too low!\n\n";}else{cout << "\nThat's it! You got it in " << tries << " guesses!\n";}} while (guess != secretNumber); // 是否猜对return 0;
}