what does '?' do?

Hi,

? is called conditional operator. more about that you can find on msdn:
http://msdn.microsoft.com/en-us/library/ty67wk28(VS.80).aspx[^]

and

http://msdn.microsoft.com/en-us/library/6a71f45d[^]

Regards
Robert

Hi this is same as ternary operator in C
It just executes the Conditional expression to the left of the ? operator. If the result satisfies (means true) it execute the expression immediate next to ? operator, otherwise it execute the expression after the : operator

if suppose year is 1996

return 1996%4==0 ? true : False

in this the compiler first execute the conditions to the left of ? operator
then

return 0==0 ? true : False

condition true so it start execute statement immediately next to ? here its return true, otherwise in this example say year =1998 the calculated value is not equal to zero It ignores the Statement immediately next to ? operator and execute the statement after the : operator which is False
hence it returns false

lets say a=10 b=15

public int void operate()
{
 c=(a>b)? a-b:a+b;
}

this is same like

if (a>b)
c=a-b;
else 
c=a+b;

for this condition c=25 because (a>b) is false. you can use this for simple conditional checking.

Although some answers let you believe that the operator is only compatible with giving boolean results (which would actually not be very useful at all) it gives you a short notation for a simple if/then/else construction.

It would be no help if you substituted this:

return value > 0;

by this:

return value > 0 ? true : false;

It would mean that your code would get longer instead of shorter. The '?' operator is meant to return any type based on the value of a boolean.

For example:

return value > 0 ? "the value is greater than zero", "the value is equal or lower  than zero";
return value > 0 ? 1 : -1;

But using it holds minor and major risks that you need to be aware of. This is because both expressions are evaluated.

This example always creates one object that will be unused:

return compressed ? new JpegImage() ? BitmapImage();

This example goes wrong if value is zero because size / value is evaluated anyway:

return value > 0 ? size / value : size;

Now just another example that would be a major bug in your software. Would the record exists, even if the action is t update the record?

return action == update ? UpdateRecord(record) : DeleteRecord(record);

Good luck!