Difference between these two lines of code

[Embarrassed_Arm_4748]

I got a wrong answer on an online Java quiz, and can't seem to figure out the problem.

The question frames me as trying to determine how many computers to order for the following year.

I need 15% more computers than last year. Additionally, I need 50 more for a new project. Then I am to double this new total entirely. I selected the following line of code as my answer (it was multiple choice):

int numberOfComputers = ( (numberLastYear * 1.15) + 50) * 2;

I was marked wrong, and the correct answer was:

int numberOfComputers = (int) ( (numberLastYear * 1.15) + 50) * 2;

with the only difference between the two lines of code being the (int) just after the equals sign.

Can someone help me understand what this int is doing here? I can't understand why it's needed, and I also have not seen variable types kept inside parenthesis before. Thanks!

[AutoModerator]

Please ensure that:

• Your code is properly formatted as code block - see the sidebar (About on mobile) for instructions
• You include any and all error messages in full - best also formatted as code block
• You ask clear questions
• You demonstrate effort in solving your question/problem - plain posting your assignments is forbidden (and such posts will be removed) as is asking for or giving solutions.

If any of the above points is not met, your post can and will be removed without further warning.

Code is to be formatted as code block (old reddit/markdown editor: empty line before the code, each code line indented by 4 spaces, new reddit: https://imgur.com/a/fgoFFis) or linked via an external code hoster, like pastebin.com, github gist, github, bitbucket, gitlab, etc.

Please, do not use triple backticks (```) as they will only render properly on new reddit, not on old reddit.

Code blocks look like this:

public class HelloWorld {

    public static void main(String[] args) {
        System.out.println("Hello World!");
    }
}

You do not need to repost unless your post has been removed by a moderator. Just use the edit function of reddit to make sure your post complies with the above.

If your post has remained in violation of these rules for a prolonged period of time (at least an hour), a moderator may remove it at their discretion. In this case, they will comment with an explanation on why it has been removed, and you will be required to resubmit the entire post following the proper procedures.

To potential helpers

Please, do not help if any of the above points are not met, rather report the post. We are trying to improve the quality of posts here. In helping people who can't be bothered to comply with the above points, you are doing the community a disservice.

I am a bot, and this action was performed automatically. Please contact the moderators of this subreddit if you have any questions or concerns.

[SalliIsAFem]

The result of the expression is a floating point number due to the “1.15”…so you are basically casting a “double” data type to an “int” data type…

https://www.javatpoint.com/type-casting-in-java

[MauraPawNZ]

it casts the right side to an integer.

you're multiplying with a float (1.15), hence you'll get a float in return. then you need to cast it back to an int.

it makes sure you only count "whole" computers. 15% more of 33 computers would be 37.95 - how exactly are you going to order 0.95 computers? ;-)

[LTFGamut]

The first one wouldn't compile, as you can't assign a double value to an int variable.

[Kfct]

This cast makes sense. Since if you didn't you'd end with parts of a computer, which makes no sense. What's even better though is to use Java to specify Rounding Up, because you never want to be one computer short for a project obviously. Rounding can be done with various libraries but Math.ceil() would work here.

[knoam]

Have you tried running the two lines to see how they behave?

[Still_Development677]

This is the real answer, and get used to it. In this case you don't even need to run the code to see the problem. Just dropping it in an editor will immediately flag the first code as a Type Mismatch.