Comparing multiple values at once using && - objective-c

Question

I have this code:
if ((total == (total1 && total2 && total3)))
{
[scrollview.contentOffset = CGPointMake (0,0)];
}
here is what it's something like on button action:
if (sender.tag == 1)
{
total1 = 10;
}
if (sender.tag == 2)
{
total2 = 20;
}
if (sender.tag == 3)
{
total3 = 30;
}
I am trying to go back to the start page of the scroll view if the user clicked the three correct buttons (similar to a password key).
Does the logical operator && work well in Objective-C, and did I use it right?

Answer 1

if ((total == (total1 && total2 && total3)))
You cannot do that. You have to explicitly compare each separately.
if ((total == total1) && (total == total2) && (total == total3)))
But that leaves the question of how total can be equal to all the three simultaneously though.

Answer 2

In your code:
if ((total == (total1 && total2 && total3)))
{
[scrollview.contentOffset = CGPointMake (0,0)];
}
When the if expression is evaluated, (total1 && total2 && total3) is evaluated first. And that can be either YES or NO (true or false if you prefer), or (0 or 1).
So your code is equivalent to the following:
BOOL allVariablesAreNotZero = total1 && total2 && total3;
if (total == allVariablesAreNotZero)
{
[scrollview.contentOffset = CGPointMake (0,0)];
}
Edit after the question was better explained
Make your buttons perform the following action when pressed:
- (void)buttonClicked:(id)sender
{
UIButton *button = (UIButton *)sender;
buttonsCombination = buttonsCombination | (1 << button.tag);
}
Where buttonsCombination is an NSUInteger. Then use the following test to see if the buttons that were pressed are the correct ones (I am doing this with three buttons, but you guess the idea)
NSUInteger correctCombination = (1 << button1) | (1 << button2) | (1 << button3)
if (buttonsCombination == correctCombination) {
// The combination is correct
} else {
// The combination is incorrect
}
buttonsCombination = 0;
Finally, note that this works because there are enough bits in a NSUInteger for 30 buttons.
Here I used bitwise operators | and <<.

Answer 3

What your current code is essentially saying is "if total is 'true' and total1, total2, and total3 are also all nonzero or if total is zero and total1, total2, and total3 are also all zero, then do something".
The && you have there is doing a logical/boolean comparison. It treats its arguments as being either true or false, and returns true if both arguments evaluate to true and false in any other case. The == compares the value of total with the true or false value that was obtained from your && expressions. That is probably not what you want here.
It seems like probably what you want to be saying is "if total is equal to the sum of total1, total2, and total3, then do something". Assuming this is the case, you would do:
if (total == (total1 + total2 + total3)) {
[scrollview.contentOffset = CGPointMake (0,0)];
}

Answer 4

Trying to determine what you mean by your comment on two other answers "i tried it but it executes the codes when i started to run the app" maybe this is what you're trying to achieve:
/* all in your button handler */
switch(sender.tag)
{
case 1:
total1 = 10;
break;
case 2:
total2 = 20;
break;
case 3:
total3 = 30;
break;
default:
break; // other buttons are ignored
}
// check it latest click means the total is now correct
if((total1 + total2 + total3) == total)
{
[scrollview.contentOffset = CGPointMake (0,0)];
}
So you update any totalX's effected by the button click and then check the condition to reset the scrolling.