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iOS Objective-C Basics (Retired) Fundamentals of C Operators and Expressions

stella J
stella J
2,234 Points
Posted by stella J
stella J
2,234 Points

between --a and a--

I can understand how value 'a' has been changed but don't get how other values are changed.

First why is 'c' 9? it's statement says 'c = a ++'...... I could understand this when I think of c as original value a..

but what I really don't understand is the change of value d. when it was 'd = --a'. it is 9 while 'd = a--', it is 10. how? why?

help me out.

2 Answers

Mike Baxter
Mike Baxter
4,442 Points
Mike Baxter
Mike Baxter
4,442 Points

Oh, that's interesting, I'd never thought of that before! But it makes sense.

--a and a-- do the same operation to the variable a. They both subtract 1 from a.

The only difference is in how it affects something else, like this variable d (or whatever you want to call it, it's just a variable).

Now, when we call

d = --a;

the operation on a happens first, before the value of d gets assigned. So d takes on the modified value of a. (Not the original value).

Alternatively, when we call

d = a--;

the operation on a happens after d gets assigned whatever a was initially. That is to say, after d takes the initial value of a, only then do we subtract 1 from a.

Personally I'm going to try to memorize it by thinking like this, the d variable is going to eat up the a as soon as it can. If it can catch it before the operation happens to a , then it will take on the original value. But if the operation happens first, then d takes the modified value of a , NOT the original.

Hopefully that helps! Let me know if I can clarify anything.

stella J
stella J
2,234 Points
stella J
stella J
2,234 Points

thank you ! it really helps me a lot : )

David Tonge
PLUS
David Tonge
Courses Plus Student 45,640 Points
David Tonge
David Tonge
Courses Plus Student 45,640 Points

I haven't taken the iOS course but I'm pretty sure the problem you're having with understanding this concept is similar to javascript. --a and a-- is kinda the same thing but the only difference is when echoed you'll get the value of the variable before the arithmetic operator is applied.