Using &&

[Lisa Beglaw]

Neither my text, or the book I just bought, explain to me how to use the && for and except is very simple ways....
a && b is true if both are true and false in all other cases.
That's it!

In my code below I am getting an error message "operator && cannot be applied to int,boolean". What can I use in it's place to make my code work?

    public void specialReport(int pickAYear)
    {
        if ((!(pickAYear >= 1930)) || (!(pickAYear <= 1969))) {
            System.out.println("Not a valid year.");
        }
        if ((pickAYear = released) && (timesRented >= 5)) {
            System.out.println("A good year for movies.");
        }
            
    }

[Abdulla Mamuwala]

In the code below, please take a look at the text in bold,

  if (([B]pickAYear = released[/B]) && (timesRented >= 5)) 

here the result of pickAYear = released will not result in a boolean, whereas the short-circuit && requires a boolean on either side that is <boolean>&&<boolean>.

What you are doing here pickAYear = released is an assignement operation.

[John Smith]

In addition to the comment above, I would refactor the negative logic:

if ((!(pickAYear >= 1930)) || (!(pickAYear <= 1969))) 

as well as the int var names that should typically be nouns. Combined everything together, it would look like this:

    public void specialReport(int year) {
        if (year < 1930 || year > 1969) {
            System.out.println("Not a valid year.");
        }
        if ((year == released) && (timesRented >= 5)) {
            System.out.println("A good year for movies.");
        }
    }
 

[Abdulla Mamuwala]

John , surely you have refactored the code,

if ((!(pickAYear >= 1930)) || (!(pickAYear <= 1969)))  

to

if (year < 1930 || year > 1969) {   

But what if the year was equal to 1930 or 1969, would'nt it be different from the logic Lisa has for pickAYear. I think the refactored code has to look like,

 if (year <= 1930 || year >= 1969) {   

[Stuart Gray]

John is right I believe.

The problem in the first version is that although the code is designed to produce an invalid year error message, it is actually testing for a valid year - and then negating it. Thats why the refactor was needed - because the original was so confusing

[Lisa Beglaw]

Man...you guys are AWESOME!!!

Once again, it was a silly beginners mistake on my part using = instead of ==...but I am a beginner so it is still allowed.

But I love the way the date code has been shortened too!!! WAY BETTER than what I have.

The reason I chose to use the ! in the dates is because of the wording of the teachers questions...
Add a method called "specialReport". This method takes a year as its parameter. If the parameter is not a year between 1930 and 1969 inclusive...blah blah blah...

But I think the samples here are WAY better and I used the ! in my last statement that finished the code.

Again, you guys have been fantastic!

[Abdulla Mamuwala]

Yes Stuart John is right, I was wrong on that one. Lisa please use John's code.

[Lisa Beglaw]

Thanks Abdulla!

[Layne Lund]

Originally posted by Lisa Beglaw:
Man...you guys are AWESOME!!!

Once again, it was a silly beginners mistake on my part using = instead of ==...but I am a beginner so it is still allowed.

But I love the way the date code has been shortened too!!! WAY BETTER than what I have.

The reason I chose to use the ! in the dates is because of the wording of the teachers questions...
Add a method called "specialReport". This method takes a year as its parameter. If the parameter is not a year between 1930 and 1969 inclusive...blah blah blah...

But I think the samples here are WAY better and I used the ! in my last statement that finished the code.

Again, you guys have been fantastic!

Boolean logic can be a little tricky when you first encounter it. If you plan on continuing programming, and assuming you are going to a university at the moment, I suggest that you take classes in Discrete Math and Logic. If your math department doesn't have a course in Logic, then check the philosophy department since it can sometimes show up there.

In short, there are many logically equivalent ways to represent the statement "the year is not a between 1930 and 1969 inclusive".

Layne

[Stuart Gray]

To be honest, what did (and always does) throw me was the double use of negation. Though John's version is my prefered one, I think even a version using just one negation would be OK (though we would probably drown in parentheses).