Preference for C# in adding, multiplication, and division

Question

How does C# execute this?

static void Main(string[] args)
    {

        int i = 4;

        i *= 4 + 8 / 2;
        Console.WriteLine(i);
    }

This was asked in one of the interview Questions. And I applied BODMAS to it. But it was wrong. Please Explain.

The multiplication and division are on different sides of the assignment operator here - I suspect that's what's causing you problems... What was your answer, and why? What have you observed the actual result to be? — Jon Skeet, Jul 31 '14 at 13:23
What did you think the right answer was? It had better be 32... — Michael Edenfield, Jul 31 '14 at 13:23
I take it you are no longer in the interview? Open your IDE, set a breakpoint and go through one F11 at a time — Sayse, Jul 31 '14 at 13:23
At the end of the interview where they ask if you have any questions, you should have asked what is the average weight of a laden African swallow in July. — Paul Zahra, Jul 31 '14 at 13:45

score 0 · Answer 1 · answered Jul 31 '14 at 13:23

0

It will be executed equivalent to the following code:

int i = 4;
int temp = 8 / 2;
temp = 4 + temp;
i = i * temp;

The compiler will shorten it down because it can calculate the constant that is on the right of i *=, so in reality it will compile to this:

int i = 4;
i *= 8;

answered Jul 31 '14 at 13:23

Lasse V. Karlsen

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may be (i*temp) is a temp by itself too. – Tigran Jul 31 '14 at 13:23
It depends on what you mean by temp, but in IL-code it will temporarily reside on the stack. – Lasse V. Karlsen Jul 31 '14 at 13:24
that's what I mean. it will again be hold in temp variable and assign after to i. – Tigran Jul 31 '14 at 13:25
@LasseV.Karlsen, so it means that Actually C# is also following BODMAS Rule. ` int i = 4; i *= 4 + 8 / 2 * 4; Console.WriteLine(i);` It gives the result as 80 in c#. and also by BODMAS Rule. – Prateik Jul 31 '14 at 13:32
The result is 32, not 80. `*=` is executed last because it's an assignment operator, not as a multiplication. – Lasse V. Karlsen Jul 31 '14 at 13:35
If the interviewer said it was 80, I hope you failed the interview because of this because to be honest, you really don't want to work there. – Lasse V. Karlsen Jul 31 '14 at 13:36
Another way to think about it is that `i *= x` is equivalent to `i = i * (x)`. – Lasse V. Karlsen Jul 31 '14 at 13:38
80 is for the this ==>> int i = 4; i *= 4 + 8 / 2 * 4 – Prateik Jul 31 '14 at 13:38
But that is a different expression. *That* will be 80. – Lasse V. Karlsen Jul 31 '14 at 13:39
So I am confused If C# Follows BODMAS Rule or not, because applying BODMAS is also giving result as 80. – Prateik Jul 31 '14 at 13:40
No it isn't, the problem is that you're not saying **how** you're applying BODMAS. You're just saying you *are*. Where did `* 4` at the end there come from? – Lasse V. Karlsen Jul 31 '14 at 13:41

score 0 · Answer 2 · answered Jul 31 '14 at 13:25

0

i *= 4 + 8 / 2 is executed as:

i = i * (4 + (8 / 2))

That's the correct way of reading it.

answered Jul 31 '14 at 13:25

jim

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score 0 · Answer 3 · answered Jul 31 '14 at 13:26

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Operator precedence is very clear on this: The / is a multiplicative operator and is applied first, then the +. The *= is an assignment operator and is applied last.

So:

8 / 2 = 4
4 + 4 = 8
i *= 8;
so i will be 4 * 8 = 32;

answered Jul 31 '14 at 13:26

Dennis_E

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Preference for C# in adding, multiplication, and division

3 Answers3