在同一个 if 测试中测试多个条件? [英] Test for multiple conditions in same if test?

问题描述

我尝试使用谷歌搜索但失败了.

I tried googling and failed.

使用 C，我有一个 IF 语句.我想针对两个不连续的值测试一个变量.

Using C, I have an IF statement. I want to test a variable against two non-consecutive values.

可以吗

if (state == 1 || 3)

if (state == 1 || 3)

表示状态为 1 或状态为 3.

Meaning if state is 1 or if state is 3.

或者必须是

if (state == 1 || state == 3)

if (state == 1 || state == 3)

我认为第一个实际上意味着 state 是 1 还是 3，这意味着测试将始终为真(如果为真或为真).

I'm thinking the first actually means if state is 1, or 3, which means the test will always be true (if true or true).

不，我不想使用 case/switch 语句.我正在尝试少打字.

No, I don't want to use a case / switch statement. I'm trying to type less.

推荐答案

你必须使用长变体

if (state == 1 || 3)

评估总是为 true 因为它被解释为

evaluates always to true because it is interpreted as

if ((state == 1) || (3))

因为在评论中问到了 C++，一位 M.M 提到了运算符重载，一个 C++ 解决方案

Because for C++ was asked in the comments an M.M mentioned operator overloading, a C++ solution

#include <cstdlib>
struct State {
    struct Proxy {
        int v;
        bool res;
        Proxy(int v, bool res) : v(v), res(res) {}

        Proxy operator || (int a) const {
            return Proxy(v, res || (a == v));
        }

        operator bool() const { return res; }
    };
    int v;
    State(int v) : v(v) {}

    Proxy operator == (int a) {
        return Proxy(v, a == v);
    }
};


int main(int argc, char *argv[])
{
    State   state(atoi(argv[1]));

    if (state == 1 || 3 || 5)
        return 1;
    else
        return 0;
}

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