算术运算符 #

一、算术运算符概述 #

C#提供了以下算术运算符：

运算符	名称	示例
+	加法	a + b
-	减法	a - b
*	乘法	a * b
/	除法	a / b
%	取余	a % b
++	自增	a++ 或 ++a
–	自减	a-- 或 --a
+	正号	+a
-	负号	-a

二、基本算术运算 #

2.1 加法运算 #

csharp

int a = 10 + 5;
int b = a + 20;
double c = 3.14 + 2.86;

string s1 = "Hello";
string s2 = "World";
string s3 = s1 + " " + s2;

2.2 减法运算 #

csharp

int a = 20 - 10;
int b = a - 5;
double c = 5.5 - 2.3;

2.3 乘法运算 #

csharp

int a = 5 * 4;
int b = a * 2;
double c = 3.5 * 2.0;

2.4 除法运算 #

csharp

int a = 20 / 4;
int b = 7 / 2;
double c = 7.0 / 2;
double d = 7 / 2.0;

整数除法注意：

csharp

int result1 = 7 / 2;
double result2 = 7.0 / 2;
double result3 = (double)7 / 2;

2.5 取余运算 #

csharp

int a = 10 % 3;
int b = 17 % 5;
int c = -10 % 3;

bool isEven = number % 2 == 0;

应用场景：

csharp

int minutes = 135;
int hours = minutes / 60;
int remainingMinutes = minutes % 60;

int lastDigit = 12345 % 10;

int page = 10;
int pageSize = 20;
int index = (page - 1) % pageSize;

三、自增自减运算符 #

3.1 前缀与后缀 #

csharp

int a = 5;
int b = ++a;

int c = 5;
int d = c++;

区别：

形式	说明	示例
++a	先加1，再使用	a=5; b=++a; → a=6, b=6
a++	先使用，再加1	a=5; b=a++; → a=6, b=5
–a	先减1，再使用	a=5; b=–a; → a=4, b=4
a–	先使用，再减1	a=5; b=a–; → a=4, b=5

3.2 详细示例 #

csharp

int x = 10;
Console.WriteLine($"x = {x}");
Console.WriteLine($"++x = {++x}");
Console.WriteLine($"x = {x}");

int y = 10;
Console.WriteLine($"y = {y}");
Console.WriteLine($"y++ = {y++}");
Console.WriteLine($"y = {y}");

3.3 在表达式中的使用 #

csharp

int a = 5;
int b = 2;
int result = a++ + ++b;

int i = 0;
int[] arr = { 1, 2, 3 };
Console.WriteLine(arr[i++]);
Console.WriteLine(arr[++i]);

四、正负号运算符 #

csharp

int a = 10;
int b = -a;
int c = -b;

int d = +a;

五、运算中的类型提升 #

5.1 自动类型提升 #

csharp

int a = 5;
double b = 2.0;
var result = a + b;

byte b1 = 10;
byte b2 = 20;
var sum = b1 + b2;

5.2 类型提升规则 #

text

byte, short, char → int → long → float → double

csharp

byte b = 10;
short s = 20;
int i = b + s;

long l = 100L;
float f = l + 1.5f;
double d = f + 2.5;

六、溢出处理 #

6.1 溢出示例 #

csharp

int max = int.MaxValue;
int overflow = max + 1;
Console.WriteLine(overflow);

6.2 checked关键字 #

csharp

try
{
    checked
    {
        int max = int.MaxValue;
        int result = max + 1;
    }
}
catch (OverflowException ex)
{
    Console.WriteLine($"溢出异常：{ex.Message}");
}

int safeResult = checked(max + 1);

6.3 unchecked关键字 #

csharp

unchecked
{
    int max = int.MaxValue;
    int result = max + 1;
}

七、数学函数 #

Math类提供常用数学函数：

csharp

double sqrt = Math.Sqrt(16);
double pow = Math.Pow(2, 10);
double abs = Math.Abs(-10);
double round = Math.Round(3.14159, 2);
double floor = Math.Floor(3.9);
double ceiling = Math.Ceiling(3.1);
double max = Math.Max(10, 20);
double min = Math.Min(10, 20);
int sign = Math.Sign(-5);

八、实战示例 #

8.1 计算器 #

csharp

public static class Calculator
{
    public static double Add(double a, double b) => a + b;
    public static double Subtract(double a, double b) => a - b;
    public static double Multiply(double a, double b) => a * b;
    public static double Divide(double a, double b)
    {
        if (b == 0)
            throw new DivideByZeroException("除数不能为零");
        return a / b;
    }
    public static double Modulo(double a, double b) => a % b;
}

8.2 数字处理 #

csharp

public static class NumberHelper
{
    public static int GetDigitCount(int number)
    {
        if (number == 0) return 1;
        int count = 0;
        while (number != 0)
        {
            number /= 10;
            count++;
        }
        return count;
    }
    
    public static int Reverse(int number)
    {
        int reversed = 0;
        while (number != 0)
        {
            reversed = reversed * 10 + number % 10;
            number /= 10;
        }
        return reversed;
    }
    
    public static int SumOfDigits(int number)
    {
        int sum = 0;
        while (number != 0)
        {
            sum += number % 10;
            number /= 10;
        }
        return sum;
    }
}

8.3 时间计算 #

csharp

public static string FormatSeconds(int totalSeconds)
{
    int hours = totalSeconds / 3600;
    int minutes = (totalSeconds % 3600) / 60;
    int seconds = totalSeconds % 60;
    return $"{hours:D2}:{minutes:D2}:{seconds:D2}";
}

九、注意事项 #

9.1 整数除法 #

csharp

double wrong = 1 / 2;
double correct = 1.0 / 2;
double correct2 = (double)1 / 2;

9.2 浮点精度 #

csharp

double a = 0.1 + 0.2;
Console.WriteLine(a);
Console.WriteLine(a == 0.3);

decimal b = 0.1m + 0.2m;
Console.WriteLine(b);
Console.WriteLine(b == 0.3m);

9.3 自增自减使用 #

csharp

int i = 0;
int result = i++ + i++ + i++;

int j = 0;
int a = j++;
int b = j++;
int c = j++;
int result = a + b + c;

十、总结 #

算术运算符要点：

运算符	说明
+ - * /	四则运算
%	取余
++ –	自增自减
checked	溢出检查

下一步，让我们学习关系运算符！