回报值问题？ [英] Return value problem?

问题描述

在这里我很惊讶输出它总是给1可以任何人PLZ解释这里有什么回报以及它是如何以及它返回的是什么？



我尝试过：

 #include< stdio.h> 
 int main（）
 {
 int a = 5，b; 
 b =有趣（a）; 
 printf（％d，b）; 
} 
 int fun（int a）
 {
返回 - && a ++; 
} 

解决方案

不要这样做。

问题在于 - 并且语言没有定义后增量和减量操作：它们可以在执行行之前，行执行之后或行执行期间完成 - 它们可以按编译器的任何顺序完成作家认为合适 - 所以他们可以从左到右，从右到左，或RPN堆栈顺序，或者......



所以你可以不知道何时执行帖子增量：它可能是：

 x = a; 
 a + = 1; 
 a  -  = 1; 
返回x&& x; 

或

 x = a; 
 a + = 1; 
 y = a; 
 a  -  = 1; 
返回x&& y; 

或其他一些组合。

在这种情况下，它可能是第二种选择 - 但它不一定是，并且玩是一个坏主意这些结果可能会有所不同，具体取决于您使用的编译器，甚至调试版本和发布版本之间的优化！

保持修改前和修改后的操作简单：使它们复杂化会使代码变得困难阅读，难以理解和不可靠！

建议：当你使用递增/递减时，不要多次使用变量，它是一个灰色区域，因为编译器可以自由重写你的代码，结果是不可预测的。



在你的情况下，你只关心 a 不等于零。在C中，对于任何变量， 0为假和非零为真。

所以你的代码意味着 true和true 并导致 1 因为它意味着 true

here i am surprised with the output it is always giving 1 can anyone plz explain what return is doing here and how and what it is returning ?

What I have tried:

#include<stdio.h>
int main()
{
int a=5,b;
b=fun(a);
printf("%d",b);
}
int fun(int a)
{
    return a--&&a++;
}

解决方案

Don't do that.
The problem is that exactly when pre- and post- increment and decrement operations are done is not defined by the language: they can be done before the line is executed, after the line is executed, or during the line execution - and they can be done in any order that the compiler writer finds appropriate - so they could be done left-to-right, or right-to-left, or RPN stack order, or ...

So you can't tell when the post increments are performed: it could be:

x = a;
a += 1;
a -= 1;
return x && x;

Or

x = a;
a += 1;
y = a;
a -= 1;
return x && y;

Or some other combination.
In this case, it's probably the second option - but it doesn't have to be and it's a bad idea to "play" with these things as the result can differ depending on the compiler you use, or even the optimisations between a debug build and a release build!
Keep pre- and post- modification operations simple: complicating them makes code hard to read, hard to understand, and unreliable!

Advice: Never use a variable more than once when you play with increment/decrement, it is a gray zone as the compiler is free to rewrite your code, the result is unpredictable.

In your case, you only care that a is different of zero. In C, for any variable, 0 is false and non zero is true.
so your code means true and true and result in 1 because it mean true.

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