int a = 10, b = 20;

Console.WriteLine(a == b);  // False
Console.WriteLine(a != b);  // True
Console.WriteLine(a > b);   // False
Console.WriteLine(a < b);   // True
Console.WriteLine(a >= 10); // True
Console.WriteLine(b <= 20); // True

string s1 = "Hello";
string s2 = "hello";

// 区分大小写
bool result1 = s1 == s2;           // False

// 不区分大小写
bool result2 = string.Equals(s1, s2, StringComparison.OrdinalIgnoreCase); // True

// Compare 方法：返回 0 表示相等，<0 表示 s1 < s2，>0 表示 s1 > s2
int result3 = string.Compare(s1, s2); // 不等于 0（H 的 ASCII 值小于 h）

// 值相等（调用 Equals 方法）
object obj1 = "hello";
object obj2 = "hello";
Console.WriteLine(obj1 == obj2);      // True（字符串重载了 ==）

// 引用相等（是否是同一个对象）
object obj3 = new object();
object obj4 = new object();
Console.WriteLine(obj3 == obj4);      // False
Console.WriteLine(ReferenceEquals(obj3, obj4)); // False

// 自定义类
class Person
{
    public string Name { get; set; }
    public override bool Equals(object obj) => obj is Person p && p.Name == Name;
    public static bool operator ==(Person a, Person b) => a?.Equals(b) ?? b is null;
    public static bool operator !=(Person a, Person b) => !(a == b);
}

int? x = null;
int? y = 5;

Console.WriteLine(x == null);  // True
Console.WriteLine(x == y);     // False（有一个为 null 则返回 False）
Console.WriteLine(x != y);     // True

int value = 50;

// 范围判断
bool inRange = value is >= 1 and <= 100;  // True

// 类型判断
object obj = "hello";
if (obj is string s && s.Length > 3) { }

// 空检查
string str = null;
if (str is not null) { }

bool a = true, b = false;

// &&：左边为 false 时，右边不执行
bool result1 = b && SomeMethod();  // SomeMethod 不会执行

// ||：左边为 true 时，右边不执行
bool result2 = a || SomeMethod();  // SomeMethod 不会执行

// & 和 |：两边都会执行（不短路）
bool result3 = b & SomeMethod();   // SomeMethod 会执行
bool result4 = a | SomeMethod();   // SomeMethod 会执行

bool a = true, b = false;

Console.WriteLine(a && b);   // False
Console.WriteLine(a || b);   // True
Console.WriteLine(!a);       // False
Console.WriteLine(a ^ b);    // True（异或）
Console.WriteLine(a ^ a);    // False

int age = 25;
bool hasId = true;

// 逻辑与：必须同时满足
if (age >= 18 && hasId)
{
    Console.WriteLine("可以进入");
}

// 逻辑或：满足一个即可
int score = 85;
if (score < 60 || score > 100)
{
    Console.WriteLine("成绩无效");
}

// 逻辑非
bool isClosed = false;
if (!isClosed)
{
    Console.WriteLine("门是开着的");
}

// 组合使用
int x = 50;
if (x > 0 && x < 100 && x != 50)
{
    Console.WriteLine("x 在 1-99 之间且不等于 50");
}

int age = 20;
string status = age >= 18 ? "成年人" : "未成年人";
// 嵌套
int score = 85;
string grade = score >= 90 ? "A" :
               score >= 80 ? "B" :
               score >= 60 ? "C" : "D";

// ?? 空合并
string name = null;
string displayName = name ?? "未知";  // "未知"

// ??= 空合并赋值
name ??= "默认值";

// ?. 空条件
string text = null;
int? length = text?.Length;  // null，不会抛异常

// 组合
string result = text?.Trim()?.ToUpper() ?? "空字符串";

// 建议用括号明确优先级
bool result = (a > 0 && b > 0) || (c > 0 && d > 0);

public class Money
{
    public decimal Amount { get; set; }

    // 重载比较运算符
    public static bool operator >(Money a, Money b) => a.Amount > b.Amount;
    public static bool operator <(Money a, Money b) => a.Amount < b.Amount;
    public static bool operator >=(Money a, Money b) => a.Amount >= b.Amount;
    public static bool operator <=(Money a, Money b) => a.Amount <= b.Amount;
    public static bool operator ==(Money a, Money b) => a.Amount == b.Amount;
    public static bool operator !=(Money a, Money b) => a.Amount != b.Amount;

    public override bool Equals(object obj) => obj is Money m && m.Amount == Amount;
    public override int GetHashCode() => Amount.GetHashCode();
}

// 使用
Money m1 = new Money { Amount = 100 };
Money m2 = new Money { Amount = 200 };
Console.WriteLine(m1 < m2);  // True