Why does the word print output in swift?

if ((buttonUp && buttonDown)==false){
    println("apple")
}

This statement says "if buttonUp and buttonDown statement is equal to false; print apple". So if either of the variables is false in any way the statement (buttonUp && buttonDown) returns false and the total if-statement becomes true.

A correct solution to this problem is:

if (!buttonUp && !buttonDown) {
   println("apple")
}

or

if (buttonUp == false && buttonDown == false) {
   println("apple")
}

Where "if buttonUp is false AND buttonDown is false; print apple".

So there is no confusion: && is AND, || is OR, ! is reverse value

Hi Steve,

To back up what Patrick is saying the OR operator is || whilst the AND operator is in fact && as you've correctly used above. From your code it looks as if you want to say (In pseudo) "If button up and button down are both false then do this".

This makes logical sense and the tidiest way to do this would be to check both variables for their Boolean value separately but within the same if statement, so in your example you've given us you would want:

if (buttonUp == false && buttonDown == false){
    println("apple")
} 

This is the same as what Jonas has posted previously and what Swift will do with the above code is first check the buttonUp variable to see if it is false and will return true or false then will do the same for buttonDown. Swift can then take the two Boolean values that have been returned and check them, if they both return True then the code below runs, if not then the code will not run.

The reason for the above nature is down to how Truth tables work for Swift (And I imagine most languages too) which are as follows:

// AND
true && true // true
true && false // false
false && true // false
false && false // false

// OR
true || true // true
true || false // true
false || true // true
false || false // false

As you can see from the above using the && operator allows that only when both Boolean values are true that the results will be true, anything else will simply return false. There is nothing wrong with your original code but for the result you are after you need a slightly different approach as when you are doing:

if ((buttonUp && buttonDown)==false){
}

You are checking to see if the result of buttonUp AND buttonDown is false once you have amalgamated the two, this is the same as: true && false // false

Which as per the truth table rings true (no pun intended!)

Operator form can certainly be a bug bear but I hope the above does at least provide some clarity. If however it still doesn't make sense or you'd like me to go through it in more detail or with more clarity please do just let me know and I'll give it another crack for you.

I could be wrong as I haven't used Swift a ton yet but I don't think what you're doing is valid Swift. In most languages you can't say if this && this == true you have to say if this == true && this == true.