C++ 百分号是什么意思？
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C++ What does the percentage sign mean?
提问by Jerry Coffin
I got this c++ macro and wonder what they mean by code%2 (the percentage sign) ?
我得到了这个 C++ 宏，想知道它们的代码%2（百分比符号）是什么意思？
#define SHUFFLE_STATEMENT_2(code, A, B)
switch (code%2)
{
case 0 : A; B; break;
case 1 : B; A; break;
}
回答by James Black
It is for taking a modulus.
它用于取模数。
Basically, it is an integer representation of the remainder.
基本上，它是余数的整数表示。
So, if you divide by 2 you will have either 0 or 1 as a remainder.
因此，如果您除以 2，您将得到 0 或 1 作为余数。
This is a nice way to loop through numbers and if you want the even rows to be one color and the odd rows to be another, modulus 2 works well for an arbitrary number of rows.
这是循环数字的好方法，如果您希望偶数行是一种颜色而奇数行是另一种颜色，则模数 2 适用于任意数量的行。
回答by Jerry Coffin
In case somebody happens to care: % really returns the remainder, notthe modulus. As long as the numbers are positive, there's no difference.
如果有人碰巧关心： % 真的返回余数，而不是模数。只要数字是正数，就没有区别。
For negative numbers there can be a difference though. For example, -3/2 can give two possible answers: -1 with a remainder of -1, or -2 with a remainder of 1. At least as it's normally used in modular arithmetic, the modulus is always positive, so the first result does not correspond to a modulus.
但是对于负数，可能会有所不同。例如，-3/2 可以给出两个可能的答案：-1 余数为 -1，或 -2 余数为 1。至少在模算术中通常使用它时，模数始终为正，因此第一个结果不对应于模数。
C89/90 and C++98/03 allow either answer though, as long as / and % produce answers that work together so you can reproduce the input (i.e. -1x2+-1->-3, -2x2+1=-3).
C89/90 和 C++98/03 允许任何一个答案，只要 / 和 % 产生一起工作的答案，这样你就可以重现输入（即 -1x2+-1->-3，-2x2+1=-3 ）。
For newer versions of the standards (C99, C11 and C++11) there's no longer any choice: integer division must round toward 0. For example -3/2 mustgive -1 with a remainder of -1. -3/2 giving -2 with a remainder of 1 is no longer allowed.
对于较新版本的标准（C99、C11 和 C++11），不再有任何选择：整数除法必须向 0 舍入。例如 -3/2必须给出 -1，余数为 -1。-3/2 给出 -2 且余数为 1 不再被允许。
回答by Mark Ransom
It means the remainder of a division. In your case, divide by 2 and the remainder will be either 0 or 1.
这意味着除法的剩余部分。在您的情况下，除以 2，余数将为 0 或 1。
回答by mouviciel
It means modulo. Usually (x % 2)discriminates odd and even numbers.
这意味着模数。通常(x % 2)区分奇数和偶数。
回答by RED SOFT ADAIR
Thats the modulo. It returns whats left after division:
这就是模数。它返回除法后剩下的东西：
10/3 will give 3. - 1 is left.
10/3 将给出 3。 - 还剩 1 个。
10%3 gives this 1.
10%3 给出了这个 1。
回答by JonH
Modulo returns the remainder that is left after division. It is helpful when you're tasked with determining even / odd / prime numbers as an example:
取模返回除法后剩下的余数。例如，当您的任务是确定偶数/奇数/质数时，它会很有帮助：
Here's an example of using it to find prime numbers:
这是使用它查找素数的示例：
int main(void)
{ int isPrime=1; int n;
{ int isPrime=1; 国际n;
cout << "Enter n: ";
cin >> n;
for (int i=1; i<=n; i++)
{
for (int j=2; j <= sqrt(static_cast<double>(i)); j++)
{
if(!(i%j))
{
isPrime=0;
break;
}
}
if (isPrime)
cout << i << " is prime" << endl;
isPrime=1;
}
return 0;
}
}
回答by Ryan Cori
It's the remainder of division. So like how 5 divided by 2 has a remainder of 1 because 2 goes into 5 2 times but that only equals four, and you got that little extra on the end
这是除法的剩余部分。所以就像 5 除以 2 的余数是 1 因为 2 进入 5 2 次但只等于 4，最后你得到了一点额外的
5 % 2 == 1
5 % 2 == 1
Note that division value isn't being calculated anywhere, so if you wanted both the whole total integer value of the division and it's remainder
请注意，除法值不会在任何地方计算，因此如果您想要除法的整个总整数值及其余数
int answer = 5 / 2;
int remainder = 5 % 2;
cout << "5 divided by 2 is " << answer << " with remainder " << remainder;
"5 divided by 2 is 2 with remainder 1"
“5 除以 2 是 2，余数是 1”
