unusual language construct

Projects Programming
1

I apologise if this is a dumb question but I can't find the answer in any of the manuals or sample code.

This piece of code was written by someone else and I have never seen it used before. Please can someone point me to a reference that describes how this works:

(State ? pos-- : pos++))

The variable State is described as boolean but I'm not sure which value relates to which of the results

pos-- the result of State ==0 or ==1?

Thanks

2

Google "C ternary operator"

3

google knows. even if you search for ?:

4

OP - what you have there is essentially a shorthand if condition - that's probably the best way to look at it.

Since 'State' will be either 0 or non-zero (false or true, respectively) this statements is saying, essentially:

If this is true ? do this : if it's not true then do this, instead

So, say I have an integer called 'num' and I want to add 1 to it if it's 0 or subtract 1 from it if it's > 0, I could do:

// Remember if num is 0 it's basically false, so the statement evaluates as false
num ? num-- : num++;

So if num >= 1 then this statement is true, since it's non-zero. We can also do this in if statements and loops if we want:

// This loop will run forever, since 1 is a numeric constant that is always true
while (1) {
 ...
}

// This code will never run, since 0 is false
int num = 0;
if (num) {
  ...
}

In a similar way we could do something like:

int num = 0;
true ? num++ : num--;

And since true is always definitely true you can be sure that num will be equal to 1 following the execution of this code.

5

rynd2it:
This piece of code was written by someone else and I have never seen it used before.
(State ? pos-- : pos++))

You probably will never see such an application of the ?: operator again.

The ?: construct selects a value by a condition,
in your case the selected value is the same in both cases, which is rather pointless.

IMHO a simple if to select between decrement and increment of pos would be easier to read.

6

Juraj:
google knows. even if you search for ?:

About 116,000,000 results (0.50 seconds)

none of them helpful

7

rynd2it:
About 116,000,000 results (0.50 seconds)

none of them helpful

sorry. google knows too much and gives me a different result

8

TheMemberFormerlyKnownAsAWOL:
Google "C ternary operator"

All right - after 40+ years programming etc I Learned a new term :slight_smile:

9

rynd2it:
About 116,000,000 results (0.50 seconds)

none of them helpful

google ternary operator
They are helpful; you might not understand them but that's another matter.

From one of the links found (Ternary Operator in C Explained)

Programmers use the ternary operator for decision making in place of longer if and else conditional statements.

10

thapthoptheep:
OP - what you have there is essentially a shorthand if condition - that's probably the best way to look at it.

Since 'State' will be either 0 or non-zero (false or true, respectively) this statements is saying, essentially:

If this is true ? do this : if it's not true then do this, instead

So, say I have an integer called 'num' and I want to add 1 to it if it's 0 or subtract 1 from it if it's > 0, I could do:

// Remember if num is 0 it's basically false, so the statement evaluates as false

num ? num-- : num++;




So if num >= 1 then this statement is true, since it's non-zero. We can also do this in if statements and loops if we want:

// This loop will run forever, since 1 is a numeric constant that is always true
while (1) {
...
}

// This code will never run, since 0 is false
int num = 0;
if (num) {
 ...
}




In a similar way we could do something like:

int num = 0;
true ? num++ : num--;




And since true is always definitely true you can be sure that num will be equal to 1 following the execution of this code.

Thanks for the detailed and informative reply, much appreciated

11

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