赋值运算符 #

一、赋值运算符概述 #

C#提供了以下赋值运算符：

运算符	示例	等价于
=	a = b	a = b
+=	a += b	a = a + b
-=	a -= b	a = a - b
*=	a *= b	a = a * b
/=	a /= b	a = a / b
%=	a %= b	a = a % b
&=	a &= b	a = a & b
\|=	a \|= b	a = a \| b
^=	a ^= b	a = a ^ b
<<=	a <<= b	a = a << b
>>=	a >>= b	a = a >> b
??=	a ??= b	a = a ?? b

二、基本赋值运算符 #

2.1 简单赋值 #

csharp

int a = 10;
string name = "张三";
double price = 99.99;

2.2 连续赋值 #

csharp

int a, b, c;
a = b = c = 10;

2.3 声明时赋值 #

csharp

int x = 10, y = 20, z = 30;
var name = "张三";
var numbers = new List<int> { 1, 2, 3 };

三、算术复合赋值 #

3.1 += 运算符 #

csharp

int a = 10;
a += 5;

string s = "Hello";
s += " World";

List<int> list = new List<int>();
list += 1;

3.2 -= 运算符 #

csharp

int a = 10;
a -= 5;

List<int> list = new List<int> { 1, 2, 3 };
list -= 1;

3.3 *= 运算符 #

csharp

int a = 10;
a *= 2;

double price = 99.99;
price *= 0.8;

3.4 /= 运算符 #

csharp

int a = 10;
a /= 2;

double total = 100;
total /= 3;

3.5 %= 运算符 #

csharp

int a = 17;
a %= 5;

四、位运算复合赋值 #

4.1 &= 运算符 #

csharp

int flags = 0b1111;
flags &= 0b1010;

[Flags]
enum Permissions { Read = 1, Write = 2, Execute = 4 }

Permissions perm = Permissions.Read | Permissions.Write;
perm &= ~Permissions.Write;

4.2 |= 运算符 #

csharp

int flags = 0b1000;
flags |= 0b0010;

Permissions perm = Permissions.Read;
perm |= Permissions.Write;

4.3 ^= 运算符 #

csharp

int flags = 0b1010;
flags ^= 0b0010;

4.4 <<= 和 >>= 运算符 #

csharp

int a = 5;
a <<= 2;

int b = 20;
b >>= 2;

五、空值合并赋值运算符 #

5.1 ??= 运算符（C# 8+） #

csharp

string name = null;
name ??= "默认名称";

List<int> list = null;
list ??= new List<int>();
list.Add(1);

5.2 与 ?? 运算符对比 #

csharp

string name = null;

name = name ?? "默认名称";

name ??= "默认名称";

5.3 应用场景 #

csharp

public class Cache
{
    private Dictionary<string, string> _data;
    
    public string Get(string key)
    {
        _data ??= new Dictionary<string, string>();
        
        if (!_data.TryGetValue(key, out var value))
        {
            value = LoadFromDatabase(key);
            _data[key] = value;
        }
        return value;
    }
}

六、赋值表达式 #

6.1 赋值作为表达式 #

csharp

int a;
int b = (a = 10) + 5;

while ((line = reader.ReadLine()) != null)
{
    Console.WriteLine(line);
}

if ((result = Calculate()) > 0)
{
    Console.WriteLine(result);
}

6.2 在循环中使用 #

csharp

int sum = 0;
int i = 0;
while ((i += 1) <= 10)
{
    sum += i;
}

6.3 在条件中使用 #

csharp

string input;
if (!string.IsNullOrEmpty(input = Console.ReadLine()))
{
    Console.WriteLine($"输入：{input}");
}

七、ref赋值（C# 7.3+） #

7.1 ref局部变量 #

csharp

int[] numbers = { 1, 2, 3, 4, 5 };
ref int refToSecond = ref numbers[1];
refToSecond = 20;

Console.WriteLine(numbers[1]);

7.2 ref条件赋值 #

csharp

int a = 10;
int b = 20;
ref int larger = ref (a > b ? ref a : ref b);
larger = 100;

八、目标类型new表达式（C# 9+） #

8.1 类型推断 #

csharp

List<int> numbers = new();
Dictionary<string, int> dict = new();
Person person = new() { Name = "张三", Age = 25 };

8.2 方法参数 #

csharp

void Process(List<int> numbers) { }

Process(new());
Process(new() { 1, 2, 3 });

九、实战示例 #

9.1 累加器 #

csharp

public class Accumulator
{
    private int _sum = 0;
    private int _count = 0;
    
    public void Add(int value)
    {
        _sum += value;
        _count += 1;
    }
    
    public double Average => _count > 0 ? (double)_sum / _count : 0;
}

9.2 配置管理 #

csharp

public class Configuration
{
    private string _connectionString;
    private int _timeout = 30;
    private bool _enableLogging;
    
    public void SetConnectionString(string connectionString)
    {
        _connectionString ??= connectionString;
    }
    
    public void Configure(int? timeout = null, bool? enableLogging = null)
    {
        if (timeout.HasValue)
            _timeout = timeout.Value;
        
        _enableLogging = enableLogging ?? _enableLogging;
    }
}

9.3 缓存实现 #

csharp

public class LazyCache<T>
{
    private T _value;
    private readonly Func<T> _factory;
    private bool _initialized;
    
    public LazyCache(Func<T> factory)
    {
        _factory = factory;
    }
    
    public T Value
    {
        get
        {
            if (!_initialized)
            {
                _value = _factory();
                _initialized = true;
            }
            return _value;
        }
    }
}

十、注意事项 #

10.1 类型兼容性 #

csharp

int a = 10;
a += 5.5;

double d = 10.5;
d += 5;

10.2 溢出检查 #

csharp

checked
{
    int max = int.MaxValue;
    max += 1;
}

10.3 空值处理 #

csharp

int? a = null;
a += 10;

string s = null;
s += "Hello";

十一、总结 #

赋值运算符要点：

运算符	说明
=	基本赋值
+= -= *= /= %=	算术复合赋值
&= \|= ^= <<= >>=	位运算复合赋值
??=	空值合并赋值

下一步，让我们学习运算符优先级！