在这段PHP代码中，“？”和“：”是什么意思？ [重复]

I'm trying to convert this PHP function to Objective-C. I can just barely read PHP to figure out what the code does. Came across this line and stopped:

$nr = (strlen($nr)-3>0)?substr($nr, 0, strlen($nr)-3):"";

What do the ? and : do here? I read the documentation to see what strlen and substr do but haven't been able to figure out how this comes together and what the new value of $nr is.

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The ?: is a ternary operator. The expression x ? y : z means if x then y else z. In this case, it would translate to something like

if strlen($nr) - 3 > 0:
    $nr = substr($nr, 0, strlen($nr) - 3)
else:
    $nr = ''

This is not Python, but if you were to break it into psuedo-Python syntax it would be

if strlen($nr) - 3 > 0:
     $nr = substr($nr, 0, strlen($nr)-3)
else:
     $nr = ""

In various languages, the ? operator is a ternary operator. This syntax does not exist in Python. The above is how you would write such a statement, though you'd have to correct the syntax in each of the if blocks, as well as the if condition.

it will translate to

if (strlen($nr)-3>0) then value of $nr is substr($nr, 0, strlen($nr)-3) 
else it is "" 

And i dont think the code is in python it looks like php or perl.