Debugging var = var2 == var3

Question

I'm currently debugging a program for a school asignment and is currently stuck at understanding this line of code.

All variables are integers.

unfinished = count == 2;

Output of that is mainly 0, but does the "==" (comparison?) actually have an affect to the values or is it completly ignored?

Program language is C

Why are you writing code that is difficult to understand? Summat wrong with using brackets? — Ed Heal, Feb 12 '14 at 20:56

score 7 · Accepted Answer · answered Feb 12 '14 at 20:56

7

unfinished = count == 2;

is evaluated as

unfinished = (count == 2);

Which is equivalent to

if (count == 2)
    unfinished = 1;
else
    unfinished = 0;

answered Feb 12 '14 at 20:56

simonc

Interesting, instead of `a = b == c? 1: 0` we can use just `a = b == c` or only `a = (b == c)` – Grijesh Chauhan Feb 18 '14 at 06:55

Tim · Answer 2 · 2014-02-12T21:26:00.910

2

if countis equal to 2, unfinished will be 1 (true), else it will be 0 (false)

edited Feb 12 '14 at 21:26

answered Feb 12 '14 at 20:55

Tim

*Right of the = is evaluated first*: No. No guarantee that right operand of `=` operator evaluates first. Order of evaluation is not guaranteed with this operator. – haccks Feb 12 '14 at 21:12
This table say it is http://www.difranco.net/compsci/C_Operator_Precedence_Table.htm – Tim Feb 12 '14 at 21:15
Are you mixing Associativity with order of evaluation? – haccks Feb 12 '14 at 21:20
1

@TimCastelijns: Precedence does not guarantee order of evaluation; the result of `count == 2` must be evaluated before it can be *assigned* to `unfinished`, but that doesn't mean `unfinished` can't be evaluated first. – John Bode Feb 12 '14 at 21:23
1

I think you are confused with **associativity** and **order of evaluation**. Read [this](http://blogs.msdn.com/b/ericlippert/archive/2008/05/23/precedence-vs-associativity-vs-order.aspx?Redirected=true) article by [Eric Lippert](http://stackoverflow.com/users/88656/eric-lippert). – haccks Feb 12 '14 at 21:23
I have done some reading and came the the conclusion i was indeed mixing up some words.. thanks for correcting me :-) – Tim Feb 12 '14 at 21:25

2 Answers2