C++_Tutorial

#include<bits/stdc++.h>
using namespace std;
typedef int feet;
typedef long long ll;
int main(){
    feet x = 5;
    ll y = 1e16 + 10;
    cout << x << endl;
    cout << y << endl;
    return 0;
}
//5
//10000000000000010

#include <bits/stdc++.h>
using namespace std;
enum Weekday {
    Sunday,          // 0
    Monday = 5,
    Tuesday,        // 6
    Wednesday,      // 7
    Thursday,
    Friday,
    Saturday
};

int main(){
    Weekday today = Wednesday;
    cout << today << endl;
    return 0;
}
// output: 7

#include <bits/stdc++.h>
using namespace std;
int main(){
    int x = 9;
    double y = static_cast<double>(x);
    cout << fixed << setprecision(6) << y * 1.0 << endl; // 设置精度保留6位小数
    return 0;
}
// 9.000000

#include<bits/stdc++.h>
using namespace std;
int main(){
    vector<int> nums = {-9, 1100, 43, 4, 300, 20};
    sort(nums.begin(), nums.end());
    //sort后数组为： -9 4 20 43 300 1100
    auto left = lower_bound(nums.begin(), nums.end(), 20);
    auto right = upper_bound(nums.begin(), nums.end(), 1000);
    cout <<"下标是:"<<static_cast<int>(left - nums.begin())<< " 数值是 ：" << *left << endl;
    cout <<"下标是:"<<static_cast<int>(right - nums.begin())<< " 数值是 ：" << *right << endl;
    //下标是:2 数值是 ：20
    //下标是:5 数值是 ：1100
    return 0;
}

#include <bits/stdc++.h>
using namespace std;
// 全局变量声明
int g = 99;

// 函数声明
int func();

int main()
{
    // 局部变量声明
    int g = 10;
    cout << g << endl;      // 10
    int kk = func();
    cout << kk << endl;     // 99
    return 0;
}

// 函数定义
int func()
{
    return g;
}

#include<bits/stdc++.h>
using namespace std;
int a = 100;
int main(){
    int a = 10;
    cout << a << endl;       // 10
    cout << ::a << endl;     // 100
    return 0;
}

#include<bits/stdc++.h>
using namespace std;
int var = -1;       // 全局变量初始化
int main(){
    ::var = 1;      // 全局变量重新赋值
    for(; ::var <= 10; ::var++){
        cout << "全局变量var =" << ::var << endl;
    }
    return 0;
}
//全局变量var =1
//全局变量var =2
//全局变量var =3
//全局变量var =4
//全局变量var =5
//全局变量var =6
//全局变量var =7
//全局变量var =8
//全局变量var =9
//全局变量var =10

#include<bits/stdc++.h>
using namespace std;
class Fruit{
public:
    static int price;
};

int Fruit::price = 100;

int main(){
    Fruit apple;
    Fruit banana;
    cout << apple.price << endl;     // 100
    cout << banana.price << endl;    // 100
    return 0;
}

#include<bits/stdc++.h>
using namespace std;

class Fruit{
public:
    int price;      // 非静态成员变量
    Fruit():price(0){} // 构造函数初始化 price
};

int main(){
    Fruit apple;
    apple.price = 100;
    Fruit banana;
    banana.price = 10;
    cout << apple.price << endl;   // 输出100
    cout << banana.price << endl;  // 输出10
    return 0;
}

#include<bits/stdc++.h>
using namespace std;
int x  = 0xFABCD;       // x 被初始化为十六进制数 0xFABCD，其十进制值为 1022189
int y = 256L;           // y 被初始化为长整型常量 256L，表示为十进制的 256
int z = 412415ul;       // z 被初始化为无符号长整型常量 412415ul，表示为十进制的 412415
const double pi = 3.1415926;
#define Length 100     // 宏定义中不应该以分号结尾
#define Width 0.8
int main(){
    cout << x << endl;
    cout << y << endl;
    cout << z << endl;
    cout << pi << endl;   // 默认情况下 cout 的输出精度是有限的。为了输出更多小数位数，可以使用 std::setprecision 设置输出精度
    cout << fixed << setprecision(10) << pi << endl;
    double area = Length * Width;
    cout << area << endl;
    return 0;
}

#include <iostream>
#include <cmath>
using namespace std;
int main ()
{
   // 数字定义
   short  s = 10;
   int    i = -1000;
   long   l = 100000;
   float  f = 230.47;
   double d = 200.374;
 
   // 数学运算
   cout << "sin(d) :" << sin(d) << endl;
   cout << "abs(i)  :" << abs(i) << endl;
   cout << "floor(d) :" << floor(d) << endl;
   cout << "sqrt(f) :" << sqrt(f) << endl;
   cout << "pow( d, 2) :" << pow(d, 2) << endl;
 
   return 0;
}
//sin(d) :-0.634939
//abs(i)  :1000
//floor(d) :200
//sqrt(f) :15.1812
//pow( d, 2) :40149.7