CODEWITHSUNDEEP
javaif-statementlogic
Samuel Johnson
Samuel Johnson

Reputation: 15

if statement logic

I've been tasked with creating a small java program for a course i'm doing, and i'm having some issues with the following block of code:

        System.out.println("Please enter your first name:");
    userName = sc.nextLine();
    System.out.println("What year were you born in?");
    birthYear = sc.nextInt();
    System.out.println("In the 'dd.mm' format, what are the day and month of your birth?");
    dayMonth = sc.nextDouble();
    //Cast the user input of type double to an int for the day of Birth
    dayOfBirth = dayMonth.intValue();

    //Cast the double value for month and cast it to an int
    dayMonth = dayMonth - dayOfBirth;
    dayMonth = dayMonth * 100;
    dayMonth = Math.rint(dayMonth);
    monthOfBirth = dayMonth.intValue();
if(birthYear == 2013 || birthYear == 2001 || birthYear == 1989 || birthYear == 1977 || birthYear == 1965 || birthYear == 1953 || birthYear == 1941)
{
    if(monthOfBirth == 9 || monthOfBirth == 10 || monthOfBirth == 11)
    {
        System.out.println(userName + " was born during Spring on " + monthOfBirthName + " " + dayOfBirth + " in Snake year " + birthYear);
    }
        else if(monthOfBirth != 9 || monthOfBirth != 10 || monthOfBirth != 11)
        {
            System.out.println(userName + " was born on " + monthOfBirthName + " " + dayOfBirth + " in Snake year " + birthYear);
        }
}
if(birthYear != 2013 || birthYear != 2001 || birthYear != 1989 || birthYear != 1977 || birthYear != 1965 || birthYear != 1953 || birthYear != 1941)
{
     if(monthOfBirth == 9 || monthOfBirth == 10 || monthOfBirth == 11)
    {
        System.out.println(userName + " was born during Spring on " + monthOfBirthName + " " + dayOfBirth + " " + birthYear);
    }   
        else if(monthOfBirth != 9 || monthOfBirth != 10 || monthOfBirth != 11)
        {
            System.out.println(userName + " was born on " + monthOfBirthName + " " + dayOfBirth + " " + birthYear);
        }
}

However my output is coming out as follows:

Please enter your first name:

Samuel

What year were you born in?

1977

In the 'dd.mm' format, what are the day and month of your birth?

09.09

Samuel was born during Spring on September 9 in Snake year 1977

Samuel was born during Spring on September 9

I obviously do not want repeated output, however i'm having trouble seeing where the logic in my if statements are causing it to be repeated.

Any help would be greatly appreciated.

Thanks all,

~ Sam.

Upvotes: 1

Views: 226

Answers (8)

Kamal
Kamal

Reputation: 5522

The problem is with 

if(birthYear != 2013 || birthYear != 2001 || birthYear != 1989 || birthYear != 1977 || birthYear != 1965 || birthYear != 1953 || birthYear != 1941

If you look carefully, we are making sure that the expression always result in try. Only one can be false at max at a time, all others will be true, hence finally it is always true (confused?). Say birth year is 2013, which makes first condition (birthyear!=2013) false, but all others will be true. Take any other example and you will see what I am trying to say.

Actually a minor modification will fix the code for you. You have already checked that if (birthyear is in given years), a simple else without any conditions will work for you.

if(birthYear == 2013 || birthYear == 2001 || birthYear == 1989 || birthYear == 1977 || birthYear == 1965 || birthYear == 1953 || birthYear == 1941)
{
    if(monthOfBirth == 9 || monthOfBirth == 10 || monthOfBirth == 11)
    {
        System.out.println(userName + " was born during Spring on " + monthOfBirthName + " " + dayOfBirth + " in Snake year " + birthYear);
    }
        else// NO CHECK REQUIRED NOW
        {
            System.out.println(userName + " was born on " + monthOfBirthName + " " + dayOfBirth + " in Snake year " + birthYear);
        }
}
//SEE THIS
else{
     if(monthOfBirth == 9 || monthOfBirth == 10 || monthOfBirth == 11)
    {
        System.out.println(userName + " was born during Spring on " + monthOfBirthName + " " + dayOfBirth + " " + birthYear);
    }   
//AND
        else 
        {
            System.out.println(userName + " was born on " + monthOfBirthName + " " + dayOfBirth + " " + birthYear);
        }
}

Upvotes: 0

Fragment
Fragment

Reputation: 1585

Better use collections instead of multiple if( ... == ..|| ... == .. ||...)

Like this:

List<String> wrongYears = Arrays.asList("2013", "2001", "1989", "1977", ...);

and check:

if(wrongYears.contains(birthYear)
{
 ...
}

and for months numbers the same

your logic errors would be obvious

Upvotes: 1

Daniel Figueroa
Daniel Figueroa

Reputation: 10666

The answer is in your conditional.

assume dob = 1

if(dob == 1 || dob == 2 || dob == 3 ...)

Will evaluate to true because dob == 1

if (dob != 1 || dob != 2 || dob != 3 ...)

Will also evaluate to true because dob != 2

What you want to use is AND / && and not OR / ||

Upvotes: 0

Majid Abarghooei
Majid Abarghooei

Reputation: 663

you can choose one of the following solutions:

1) using && operator instead of || in 2nd if statement

or

2) if(){}else{} // Kamal's Solution

Upvotes: 1

Seb
Seb

Reputation: 313

The second if part is wrong:

if(birthYear != 2013 || birthYear != 2001 || ....)

because it is alway true. Just check a view examples: If you have 2012, It is not 2013 so your expression becomes true. If you take 2013 then the first part becomes false, but when you evaluate 2013 != 2001, it becomes true again.

What you probably want to have is 

if(birthYear == 2013 || birthYear == 2001 || birthYear == 1989 || birthYear == 1977 || birthYear == 1965 || birthYear == 1953 || birthYear == 1941)
{
.....
}
else {
.....
}

By the way: If you want to negate the expression (x == A || x == B || x == C) then the logical negation is (x!=A && x!=B && x!=C).

Upvotes: 0

AlexanderBrevig
AlexanderBrevig

Reputation: 1987

You should replace the second if where everything is != with a simple 'else' because you have already checked if any of the statements are true. As such, simply writing else will be logically equal and much more readable.

if(birthYear == 2013 || birthYear == 2001 || birthYear == 1989 || birthYear == 1977 || birthYear == 1965 || birthYear == 1953 || birthYear == 1941){
    ....
}
else { //not snake year
    ....
}

Upvotes: 0

javadev
javadev

Reputation: 1669

Use else statement where possible, so if you test for 2013, 2001 ... Just after, make an else statement

Upvotes: 0

Rahul
Rahul

Reputation: 45060

Instead of using 2 if separately, make them either if-else or if-else if.

if(birthYear == 2013 || birthYear == 2001 || birthYear == 1989 || birthYear == 1977 || birthYear == 1965 || birthYear == 1953 || birthYear == 1941){
    ....
}
else if(birthYear != 2013 || birthYear != 2001 ||...){
....
}

Because, if you give a if-if, both the if statements will be executed, whereas, if you give an if-else if, the second else if will be executed only if the first if statement fails.

Upvotes: 1

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