C++ 错误：“表达式必须具有整数或无作用域的枚举类型”

Error: "expression must have integral or unscoped enum type"

提问by Victor Martins

So guys I'm new I tried looking up a solution however, I didn't really understand it that well, I'm writing shorthand to understand how they can be replaced with other pieces of code, so I ran across the modulus to which I added however it gives a "expression must have integral or unscoped enum type".

所以伙计们，我是新手，我尝试寻找一个解决方案，但是，我并没有真正理解它，我正在编写速记以了解如何用其他代码段替换它们，所以我遇到了模数但是我补充说，它给出了 “表达式必须具有整数或无作用域的枚举类型”。

I don't know enum type is exactly, they code doesn't run?

我不知道 enum 类型到底是什么，他们的代码不运行？

#include<iostream>
#include<string>
using namespace std;

int main() {

    double b, x, y, z, a, c;

    c, b, x, y, z, a, c = 100;
    x += 5;
    y -= 2;
    z *= 10;
    a /= b;
    c %= 3; // "c" seems to be giving out that error?


    cout << b << x << y << z << a << c;


    return 0;
}

the problem here is that "c" gives the "expression must have integral or unscoped enum type"error.

这里的问题是“c”给出了“表达式必须具有整数或无作用域枚举类型”错误。

I know what the modulus does, it gives the remainder of the division between 2 numbers, however I'm stumped in this case because should it gives a remainder? Is it syntactically wrong?

我知道模数的作用，它给出了两个数字之间的余数，但是在这种情况下我很难过，因为它应该给出余数吗？它在语法上是错误的吗？

回答by gsamaras

cis double, thus you cannot use the modulo operator %.

c是 double，因此您不能使用模运算符%。

Use fmod()instead.

请改用fmod()。

So change this:

所以改变这个：

c %= 3

to this:

对此：

c = fmod(c, 3);

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As Slava mentioned, you could have used an intinstead, like this:

正如 Slava 所提到的，您可以使用 anint来代替，如下所示：

int c = 5; // for example
c %= 3

which wouldn't require the use of fmod(). It's important to understand that the modulo operator %works with ints.

这不需要使用fmod(). 了解模运算符%与ints一起使用很重要。

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As π?ντα ρ?ι mentioned, there is also this: Can't use modulus on doubles?

正如 π?ντα ρ?ι 所提到的，还有这个：不能在双打上使用模数吗？

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As a side note Victor, you have so many variables, but most of them are unused and or uninitialized. Did you compile with all the warnings enabled? Here is what I get when compiling your original code (with the line that generates the error commented out):

作为旁注 Victor，您有很多变量，但其中大部分未使用或未初始化。您是否在启用所有警告的情况下进行编译？这是编译原始代码时得到的结果（注释掉生成错误的行）：

C02QT2UBFVH6-lm:~ gsamaras$ g++ -Wall main.cpp 
main.cpp:9:5: warning: expression result unused [-Wunused-value]
    c, b, x, y, z, a, c = 100;
    ^
main.cpp:9:8: warning: expression result unused [-Wunused-value]
    c, b, x, y, z, a, c = 100;
       ^
main.cpp:9:11: warning: expression result unused [-Wunused-value]
    c, b, x, y, z, a, c = 100;
          ^
main.cpp:9:14: warning: expression result unused [-Wunused-value]
    c, b, x, y, z, a, c = 100;
             ^
main.cpp:9:17: warning: expression result unused [-Wunused-value]
    c, b, x, y, z, a, c = 100;
                ^
main.cpp:9:20: warning: expression result unused [-Wunused-value]
    c, b, x, y, z, a, c = 100;
                   ^
main.cpp:10:5: warning: variable 'x' is uninitialized when used here [-Wuninitialized]
    x += 5;
    ^
main.cpp:7:16: note: initialize the variable 'x' to silence this warning
    double b, x, y, z, a, c;
               ^
                = 0.0
main.cpp:11:5: warning: variable 'y' is uninitialized when used here [-Wuninitialized]
    y -= 2;
    ^
main.cpp:7:19: note: initialize the variable 'y' to silence this warning
    double b, x, y, z, a, c;
                  ^
                   = 0.0
main.cpp:12:5: warning: variable 'z' is uninitialized when used here [-Wuninitialized]
    z *= 10;
    ^
main.cpp:7:22: note: initialize the variable 'z' to silence this warning
    double b, x, y, z, a, c;
                     ^
                      = 0.0
main.cpp:13:5: warning: variable 'a' is uninitialized when used here [-Wuninitialized]
    a /= b;
    ^
main.cpp:7:25: note: initialize the variable 'a' to silence this warning
    double b, x, y, z, a, c;
                        ^
                         = 0.0
main.cpp:13:10: warning: variable 'b' is uninitialized when used here [-Wuninitialized]
    a /= b;
         ^
main.cpp:7:13: note: initialize the variable 'b' to silence this warning
    double b, x, y, z, a, c;
            ^
             = 0.0
11 warnings generated.