如何计算整数的除法和模数？

Question

如何计算C#中整数的除法和模数？

Answer 1

在提出此类问题之前,请查看MSDN文档.

除以两个整数后,结果始终为整数.例如,7/3的结果是2.要确定7/3的余数,请使用余数运算符(%).

int a = 5;
int b = 3;

int div = a / b; //quotient is 1
int mod = a % b; //remainder is 2

Answer 2

还有 Math.DivRem

quotient = Math.DivRem(dividend, divisor, out remainder);

Answer 3

使用/运营商执行分部:

result = a / b;

Modulo除法使用%运算符完成:

result = a % b;

Answer 4

有趣的事实!

'模数'操作定义为:

a % n ==> a - (a/n) * n

参考:模块化算术

所以你可以自己动手,虽然它比内置%运算符慢FAR:

public static int Mod(int a, int n)
{
    return a - (int)((double)a / n) * n;
}

编辑:哇,最初在这里发生了相当严重的错误,感谢@joren抓住了我

现在我在这里依赖的事实是C#中的division + cast-to-int相当于Math.Floor(即,它会丢弃分数),但是"真正的"实现将改为:

public static int Mod(int a, int n)
{
    return a - (int)Math.Floor((double)a / n) * n;
}

实际上,您可以通过以下方式查看%和"true modulus"之间的差异:

var modTest =
    from a in Enumerable.Range(-3, 6)
    from b in Enumerable.Range(-3, 6)
    where b != 0
    let op = (a % b)
    let mod = Mod(a,b)
    let areSame = op == mod
    select new 
    { 
        A = a,
        B = b,
        Operator = op, 
        Mod = mod, 
        Same = areSame
    };
Console.WriteLine("A      B     A%B   Mod(A,B)   Equal?");
Console.WriteLine("-----------------------------------");
foreach (var result in modTest)
{
    Console.WriteLine(
        "{0,-3} | {1,-3} | {2,-5} | {3,-10} | {4,-6}", 
        result.A,
        result.B,
        result.Operator, 
        result.Mod, 
        result.Same);
}

结果:

A      B     A%B   Mod(A,B)   Equal?
-----------------------------------
-3  | -3  | 0     | 0          | True  
-3  | -2  | -1    | -1         | True  
-3  | -1  | 0     | 0          | True  
-3  | 1   | 0     | 0          | True  
-3  | 2   | -1    | 1          | False 
-2  | -3  | -2    | -2         | True  
-2  | -2  | 0     | 0          | True  
-2  | -1  | 0     | 0          | True  
-2  | 1   | 0     | 0          | True  
-2  | 2   | 0     | 0          | True  
-1  | -3  | -1    | -1         | True  
-1  | -2  | -1    | -1         | True  
-1  | -1  | 0     | 0          | True  
-1  | 1   | 0     | 0          | True  
-1  | 2   | -1    | 1          | False 
0   | -3  | 0     | 0          | True  
0   | -2  | 0     | 0          | True  
0   | -1  | 0     | 0          | True  
0   | 1   | 0     | 0          | True  
0   | 2   | 0     | 0          | True  
1   | -3  | 1     | -2         | False 
1   | -2  | 1     | -1         | False 
1   | -1  | 0     | 0          | True  
1   | 1   | 0     | 0          | True  
1   | 2   | 1     | 1          | True  
2   | -3  | 2     | -1         | False 
2   | -2  | 0     | 0          | True  
2   | -1  | 0     | 0          | True  
2   | 1   | 0     | 0          | True  
2   | 2   | 0     | 0          | True