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c++从入门到放弃.md

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  • Windows10下载MinGW
  • 点击页面中的x86_64-8.1.0-release-posix-seh-rt_v6-rev0.7z 进行下载
  • 下载完成后把 bin 目录放入系统环境变量即可在终端使用 c++ 命令进行编译 .cpp 源代码

Hello World

  • MyFirstApp
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#include <iostream>

int main(){
    std::cout << "Hello World! \n"; // this will output to the console hello world
    system("pause>0");
}
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# 编译
g++ .\MyFirstApp.cpp

# 运行
.\a.exe

  • 换行 \n 或 << endl;

  • 编译命令 g++ [source file] -o [output filename]

Variables

  • 命名
    • 构成: 下划线, 字母(区分大小写), 数字(不可数字开头)
    • 一般用小驼峰命名法

Data types

类型 定义 size(bytes) 说明
整数 int 4 -2147483648 to 2147483647
字符 char 1 单引号为字符 ‘a’
字符串 string 双引号为字符串 “character”
布尔 bool 1 true / false
浮点数 float 4
大浮点数 double 8

Data type overflow

  • 变量的值超过其内存空间, 类似钟表指针, 13 点 = 1 点 (INT_MAX + 1 = INT_MIN)

ASCII table

  • asign characters to number (it’s for American)
  • ASCII extends: utf-(1-16) (for others)
  • 字符转换为ASCII数字 (int)'a' 和 int('a') 两种写法

Condition Statement

语法

if(){}elif(){}else(){}

  • 注: 如果 {} 内只有一行代码, 可以不写 {}
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#include <iostream>
using namespace std;

int main(int argc, char const *argv[])
{
    //User enters side lengths of a triangle (a, b, c)
    //Program should write out whethre that triangle is
    //equilateral, isosceles or scalene
    float a, b, c;
    cout << "a, b, c: ";
    cin >> a >> b >> c;
    
    if (a == b && b == c)
        cout << "Equilateral triangle";
    else
    {
        if (a != b && a != c && b != c)
            cout << "Scalene triangle";
        else
            cout << "Isosceles triangle";
    }

    return 0;
}

Operators

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#include <iostream>
using namespace std;

int main(int argc, char const *argv[])
{
    // 执行优先级 从上到下
    // + - * / %
    cout << 1 + 1 << endl;
    cout << 5 / 2 << endl;  // 2
    cout << 5.0 / 2 << endl;  // 2.5

    // ++, --
    int counter = 7;
    counter++;
    cout << counter << endl;
    counter--;
    cout << counter << endl;

    int counter2 = 7;
    cout << counter2++ << endl;  // 7
    cout << counter2 << endl;  // 8
    cout << ++counter2 << endl;  // 9

    system("cls"); // clear console

    // <, >, <=, >=, ==, !=
    int a = 5, b = 5;
    // cout << (a > b) << endl;  // 0 for false (1 for true)

    // &&, ||, !
    int c = 8, d = 9;
    // cout << !(c == 5 && b == 9);

    // 优先级
    cout << (c == 8 && d == 4 + 5);  // 1

    // =, +=, -=, *=, /=, %=
    int x = 5;
    x += 7;  //same as: x = x + 7
    cout << x << endl;

    return 0;
}

三目

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#include <iostream>
using namespace std;

int main(int argc, char const *argv[])
{
    int hostUserNum, guestUserNum;
    cout << "HOST: ";
    cin >> hostUserNum;
    system("cls");
    cout << "Guest: ";
    cin >> guestUserNum;

    (hostUserNum == guestUserNum)? cout << "Correct!": cout << "Failed!";

    return 0;
}

switch case

注意每个case后面必需接break退出, 因为程序只判断一次case条件, 进入一次后, 其他的case不会再判断, 会运行下面的所有case.

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#include <iostream>
using namespace std;

int main(int argc, char const *argv[])
{
    float num1, num2;
    char operation;
    cout << "Caculator" << endl;
    cin >> num1 >> operation >> num2;

    switch (operation)
    {
    case '-':cout << num1 << operation << num2 << "=" << num1 - num2;
break;
    case '+':cout << num1 << operation << num2 << "=" << num1 + num2; break;
    case '*':cout << num1 << operation << num2 << "=" << num1 * num2; break;
    case '/':cout << num1 << operation << num2 << "=" << num1 / num2; break;
    case '%':
        bool isNum1Int, isNum2Int;
        isNum1Int = (int(num1) == num1);
        isNum2Int = (int(num2) == num2);

        if (isNum1Int && isNum2Int)
            cout << num1 << operation << num2 << "=" << int(num1) % int(num2);
        else
            cout << "Not valid!";

    break;
    
    default:cout << "Not valid opeation!"; break;
    }

    return 0;
}