执行上述代码后，n，a，b，C的值是多少？ [英] What is the value of n, a, b, C after executing the above code?

问题描述

int a=1, b=4, c=3, n;
n=(++a*b)-(c--);
a=b++*b++*b++;

执行上述操作后，n，a，b，c的值是多少代码？



我的尝试：



n =（++ 4） - （3--）= 5-2 = 3 - 正确吗？



a = 4 ++ * 4 ++ * 4 ++ = 5 * 5 * 5 = 125 - 正确吗？

What is the value of n, a, b, c after executing the above code?

What I have tried:

n=(++4)-(3--) = 5-2 = 3 — Correct?

a=4++*4++*4++ = 5*5*5 = 125 — Correct?

推荐答案

运行代码并亲眼看看。作为一般规则，这样的表达式不能保证你期望的结果，所以不要使用它们。

Run the code and see for yourself. And as a general rule such expressions will not guarantee the results you expect, so do not use them.

读这个：

C运营商优先级 - cppreference.com [ ^ ]

read this:
C Operator Precedence - cppreference.com[^]

// This line
n=(++a*b)-(c--);
// translate to
++a;
n=(a*b)-(c);
c--;

此行处于灰色区域并依赖于编译器，因此无法预测：

this line is in gray zone and depend on compiler, thus it is unpredictable:

a=b++*b++*b++;
// can be
a=4*4*4;
// as well as
a=4*5*6;

使用调试器查看你的代码到底在做什么。



有一个工具可以让你看到你的代码在做什么，它的名字是调试器。它也是一个很好的学习工具，因为它向你展示了现实，你可以看到哪种期望与现实相符。

当你不明白你的代码在做什么或为什么它做它做的时候，答案就是答案是调试器。

使用调试器查看代码正在执行的操作。只需设置断点并查看代码执行情况，调试器允许您逐行执行第1行并在执行时检查变量。



调试器 - 维基百科，免费的百科全书 [ ^ ]



掌握Visual Studio 2010中的调试 - 初学者指南 [ ^ ]

使用Visual Studio 2010进行基本调试 - YouTube [ ^ ]

调试器在这里向您展示您的代码正在做什么，您的任务是与什么进行比较应该这样做。

调试器中没有魔法，它没有找到错误，它只是帮助你。当代码没有达到预期的效果时，你就接近了一个bug。

Use the debugger to see what your code is really doing.

There is a tool that allow you to see what your code is doing, its name is debugger. It is also a great learning tool because it show you reality and you can see which expectation match reality.
When you don't understand what your code is doing or why it does what it does, the answer is debugger.
Use the debugger to see what your code is doing. Just set a breakpoint and see your code performing, the debugger allow you to execute lines 1 by 1 and to inspect variables as it execute.

Debugger - Wikipedia, the free encyclopedia[^]

Mastering Debugging in Visual Studio 2010 - A Beginner's Guide[^]
Basic Debugging with Visual Studio 2010 - YouTube[^]
The debugger is here to show you what your code is doing and your task is to compare with what it should do.
There is no magic in the debugger, it don't find bugs, it just help you to. When the code don't do what is expected, you are close to a bug.

只是为了说明一个真实的例子，这些表达式的值可以依赖于编译器，试试这个简单的修改：

Just to illustrate through a real example, that the value of such expressions can be compiler dependent, try with this simple modification:

a=b++*++b*++b;

使用gcc（编译器），对于'a'

和bcc32（Borland C ++编译器）你得到150的值得到216为'a'。



要知道'为什么'，你需要看到汇编语言输出

With gcc (compiler) you get value of 150 for 'a'
and with bcc32 (Borland C++ compiler) you get 216 for 'a'.

To know 'why', you will need to see the assembly language output

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