关系运算符 #

一、关系运算符概述 #

关系运算符用于比较两个值，返回布尔结果（true或false）。

运算符	名称	示例
==	等于	a == b
!=	不等于	a != b
>	大于	a > b
<	小于	a < b
>=	大于等于	a >= b
<=	小于等于	a <= b

二、基本比较运算 #

2.1 等于运算符 #

csharp

int a = 10;
int b = 10;
bool isEqual = a == b;

string s1 = "Hello";
string s2 = "Hello";
bool sameString = s1 == s2;

bool sameReference = object.ReferenceEquals(s1, s2);

2.2 不等于运算符 #

csharp

int a = 10;
int b = 20;
bool notEqual = a != b;

string s1 = "Hello";
string s2 = "World";
bool different = s1 != s2;

2.3 大于小于运算符 #

csharp

int a = 10;
int b = 20;

bool greater = a > b;
bool less = a < b;
bool greaterOrEqual = a >= 10;
bool lessOrEqual = b <= 20;

三、数值比较 #

3.1 整数比较 #

csharp

int age = 25;

if (age >= 18)
{
    Console.WriteLine("成年人");
}

if (age < 60)
{
    Console.WriteLine("未退休");
}

3.2 浮点数比较 #

csharp

double a = 0.1 + 0.2;
double b = 0.3;

bool equal = a == b;

double epsilon = 1e-10;
bool approximatelyEqual = Math.Abs(a - b) < epsilon;

3.3 Decimal比较 #

csharp

decimal price1 = 99.99m;
decimal price2 = 99.99m;

bool samePrice = price1 == price2;

四、字符串比较 #

4.1 == 运算符 #

csharp

string s1 = "Hello";
string s2 = "Hello";
string s3 = "hello";

bool equal1 = s1 == s2;
bool equal2 = s1 == s3;

4.2 Equals方法 #

csharp

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

bool equal = s1.Equals(s2);
bool equalIgnoreCase = s1.Equals(s2, StringComparison.OrdinalIgnoreCase);

4.3 Compare方法 #

csharp

string s1 = "apple";
string s2 = "banana";

int result = string.Compare(s1, s2);

if (result < 0)
    Console.WriteLine("s1 < s2");
else if (result > 0)
    Console.WriteLine("s1 > s2");
else
    Console.WriteLine("s1 == s2");

4.4 StringComparison #

csharp

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

bool equal1 = string.Equals(s1, s2, StringComparison.Ordinal);
bool equal2 = string.Equals(s1, s2, StringComparison.OrdinalIgnoreCase);
bool equal3 = string.Equals(s1, s2, StringComparison.CurrentCulture);

五、引用类型比较 #

5.1 引用相等 #

csharp

public class Person
{
    public string Name { get; set; }
}

var p1 = new Person { Name = "张三" };
var p2 = new Person { Name = "张三" };
var p3 = p1;

bool sameRef1 = p1 == p2;
bool sameRef2 = p1 == p3;
bool sameRef3 = object.ReferenceEquals(p1, p2);

5.2 重写Equals #

csharp

public class Person : IEquatable<Person>
{
    public string Name { get; set; }
    public int Age { get; set; }
    
    public override bool Equals(object obj)
    {
        return Equals(obj as Person);
    }
    
    public bool Equals(Person other)
    {
        if (other is null) return false;
        return Name == other.Name && Age == other.Age;
    }
    
    public override int GetHashCode()
    {
        return HashCode.Combine(Name, Age);
    }
    
    public static bool operator ==(Person left, Person right)
    {
        if (left is null) return right is null;
        return left.Equals(right);
    }
    
    public static bool operator !=(Person left, Person right)
    {
        return !(left == right);
    }
}

六、可空类型比较 #

6.1 可空值类型 #

csharp

int? a = 10;
int? b = 10;
int? c = null;

bool equal1 = a == b;
bool equal2 = a == c;
bool equal3 = c == null;

6.2 可空引用类型 #

csharp

string? s1 = null;
string? s2 = null;

bool equal = s1 == s2;

七、is运算符 #

7.1 类型检查 #

csharp

object obj = "Hello";

if (obj is string)
{
    Console.WriteLine("是字符串");
}

if (obj is int)
{
    Console.WriteLine("是整数");
}

7.2 模式匹配 #

csharp

object obj = 42;

if (obj is int number)
{
    Console.WriteLine($"整数：{number}");
}

if (obj is string text)
{
    Console.WriteLine($"字符串：{text}");
}

7.3 类型模式 #

csharp

object value = 42;

string result = value switch
{
    int i => $"整数：{i}",
    double d => $"浮点数：{d}",
    string s => $"字符串：{s}",
    null => "null",
    _ => "其他类型"
};

八、条件表达式中的使用 #

8.1 if语句 #

csharp

int score = 85;

if (score >= 90)
{
    Console.WriteLine("优秀");
}
else if (score >= 80)
{
    Console.WriteLine("良好");
}
else if (score >= 60)
{
    Console.WriteLine("及格");
}
else
{
    Console.WriteLine("不及格");
}

8.2 三元运算符 #

csharp

int age = 20;
string status = age >= 18 ? "成年" : "未成年";

int number = -5;
int abs = number >= 0 ? number : -number;

8.3 while循环 #

csharp

int count = 0;
while (count < 10)
{
    Console.WriteLine(count);
    count++;
}

九、实战示例 #

9.1 范围检查 #

csharp

public static bool IsInRange(int value, int min, int max)
{
    return value >= min && value <= max;
}

public static bool IsValidAge(int age)
{
    return age >= 0 && age <= 150;
}

public static bool IsValidScore(int score)
{
    return score >= 0 && score <= 100;
}

9.2 字符串验证 #

csharp

public static bool IsValidEmail(string email)
{
    return email != null && email.Contains("@") && email.Contains(".");
}

public static bool IsValidPhoneNumber(string phone)
{
    return phone != null && phone.Length == 11 && phone.StartsWith("1");
}

9.3 对象比较 #

csharp

public class Range
{
    public int Min { get; }
    public int Max { get; }
    
    public Range(int min, int max)
    {
        Min = min;
        Max = max;
    }
    
    public bool Contains(int value)
    {
        return value >= Min && value <= Max;
    }
    
    public bool Overlaps(Range other)
    {
        return Min <= other.Max && Max >= other.Min;
    }
}

十、最佳实践 #

10.1 浮点数比较 #

csharp

public static bool ApproximatelyEqual(double a, double b, double epsilon = 1e-10)
{
    return Math.Abs(a - b) < epsilon;
}

10.2 字符串比较 #

csharp

public static bool EqualsIgnoreCase(string a, string b)
{
    return string.Equals(a, b, StringComparison.OrdinalIgnoreCase);
}

10.3 空值检查 #

csharp

public static bool IsNullOrEmpty(string value)
{
    return string.IsNullOrEmpty(value);
}

public static bool IsNullOrWhiteSpace(string value)
{
    return string.IsNullOrWhiteSpace(value);
}

十一、总结 #

关系运算符要点：

运算符	说明
== !=	相等比较
> <	大于小于
>= <=	大于等于、小于等于
is	类型检查

下一步，让我们学习逻辑运算符！