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While Loop with Sentinel issues  RSS feed

 
Amie Mac
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Hello fellow ranchers,

I have been racking my brain on trying to figure out how to write the code for a while loop with a sentinel value which calls a variable (actually I think it will call a get method) from another class. I was able to get it to work when I had the variable in the same class, but when I handed in the assignment my instructor advised that I shouldn't declare the variables in the main program and they should all be in the employee.java file. He also stated that the while loops in my set methods shouldn't be there and be put into the main as well.

So I modified the program and I moved the while loops out of the set methods and I ended up using a while (true) look to get the sentinel value to work. I have read that using the while (true) and calling a break is not best practices so I am not satisfied with the program.

I have turned it in this way, but for my learning purposes, I would like to figure out how to use the while loop like I did in my first submission and not using the while(true). I think that it's an issue of getting the input.nextLine() into the loop somehow so that it will "listen" for the value that is being entered in the console. But every which way I tried, the program gave compile errors. I don't have all the "tries" and the errors... I would have to recreate them if anyone wanted to see that...

Can someone take a look and let me know what is needed in my code to get it to work like my first submitted assignment?

So... here is all the code for what I submitted for my assignment.

This is from my first submitted assignment:




And this is from the revised submission of the assignment with the while (true) loop:



 
Amie Mac
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To make things a bit clearer (hopefully), it is these lines that I would like to get working in the rework of the program where I used the while (true):

 
Carey Brown
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I don't have any problems with your revised code. What's not working for you? Errors? Incorrect output?
 
Knute Snortum
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There are a lot of opinions on this, so I'll just tell you mine.

Generally, I like to use do/while loops if I'm going to do something at least once. This will avoid the "printing the prompt twice" issue you have.

Second, I wouldn't set the employee name when I know it's incorrect. So create some kind of input variable to test.

Now, if you have the outer do/while loop and an input variable, what ends the loop? I think you know.

There are two camps on the use of break. One says never use it. I think that's a bit extreme. I wouldn't have a problem with this:



This is just an example. You can do it other ways too.
 
Amie Mac
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Carey Brown wrote:I don't have any problems with your revised code. What's not working for you? Errors? Incorrect output?

Nothing is necessarily wrong with the revised code. It works as expected. I was just wondering if there is a better way to write it.
 
Liutauras Vilda
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I know that assignment marking grids has line "is code clearly commented...", but that is the way too much.
You did good on choosing very clear class, methods, variables names and it is more important than comments, especially when they don't say anything new than code itself.
In practice never comment each line of code - it makes code unreadable.
 
Paul Clapham
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Amie Mac wrote:Nothing is necessarily wrong with the revised code. It works as expected. I was just wondering if there is a better way to write it.


When I was a beginner I thought that form of while-loop with the side-effect of assigning a String to a variable was kind of icky. But it's a common idiom and people do get used to it once they've seen it a few times. So I would leave it that way.
 
Campbell Ritchie
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Paul Clapham wrote: . . . that form of while-loop with the side-effect of assigning a String to a variable . . .
Agree with Paul C: that is a common idiom. But it does read strangely when you first see it, and you would never guess it if nobody showed you how to do it.
 
Amie Mac
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Knute Snortum wrote:There are a lot of opinions on this, so I'll just tell you mine.

Generally, I like to use do/while loops if I'm going to do something at least once. This will avoid the "printing the prompt twice" issue you have.

Second, I wouldn't set the employee name when I know it's incorrect. So create some kind of input variable to test.

Now, if you have the outer do/while loop and an input variable, what ends the loop? I think you know.

There are two camps on the use of break. One says never use it. I think that's a bit extreme. I wouldn't have a problem with this:



This is just an example. You can do it other ways too.


Yes, I like this do... while loop better than the while (true) loop that I have in my code. I will have to try it out this way at some point. Thanks for your input.
 
Amie Mac
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Liutauras Vilda wrote:I know that assignment marking grids has line "is code clearly commented...", but that is the way too much.
You did good on choosing very clear class, methods, variables names and it is more important than comments, especially when they don't say anything new than code itself.
In practice never comment each line of code - it makes code unreadable.


Yes, I don't like all the comments in the code either, because it does make it harder to read... I just wanted to make sure it was clearly commented.
Thanks for the tip!
 
Amie Mac
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Campbell Ritchie wrote:
Paul Clapham wrote: . . . that form of while-loop with the side-effect of assigning a String to a variable . . .
Agree with Paul C: that is a common idiom. But it does read strangely when you first see it, and you would never guess it if nobody showed you how to do it.


Thank you Paul and Campbell... I am glad that there are places out there like Code Ranch that can assist with code writing since the textbooks don't have all the examples.
 
Campbell Ritchie
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You're welcome

By the way: do you understand the syntax of that loop and why there have to ybe certain () in certain places?
A style thing: you should not usually have those spaces after ( or before ). We have some style suggestions of our own.
 
Amie Mac
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Campbell Ritchie wrote:You're welcome

By the way: do you understand the syntax of that loop and why there have to ybe certain () in certain places?

Do you mean the () in this part of the loop code?

Do the () mean that it is a method and arguments or parameters can be passed to the method?

A style thing: you should not usually have those spaces after ( or before ). We have some style suggestions of our own.

Thank you. I read through these style suggestions and in there it is suggested to not use do... while loops.

 
Campbell Ritchie
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You got that bit right, but I actually meant the next pair of () outside that.
[Edit]Also, I meant in the line beginning while. Look in your first post, Payroll class, line 30.
 
Amie Mac
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Campbell Ritchie wrote:You got that bit right, but I actually meant the next pair of () outside that.
[Edit]Also, I meant in the line beginning while. Look in your first post, Payroll class, line 30.


Do you mean this line?

I think that we have 3 methods here:
while()
input.nextLine()
equalsIgnoreCase()

but I am not sure why there are () around firstName = input.nextLine(). Is it because of the "!" ?
 
Carey Brown
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Amie Mac wrote:
I think that we have 3 methods here:
while()
input.nextLine()
equalsIgnoreCase()

but I am not sure why there are () around firstName = input.nextLine(). Is it because of the "!" ?

You need those () because the assignment (=) operator has a lower precedence and you want the assignment to take place before the call to equalsIgnoreCase().
 
Amie Mac
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Carey Brown wrote:
Amie Mac wrote:
I think that we have 3 methods here:
while()
input.nextLine()
equalsIgnoreCase()

but I am not sure why there are () around firstName = input.nextLine(). Is it because of the "!" ?

You need those () because the assignment (=) operator has a lower precedence and you want the assignment to take place before the call to equalsIgnoreCase().


Ahh... yes. That makes sense.
Thanks
 
Campbell Ritchie
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That was what I wanted to know that you understood.
 
Liutauras Vilda
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And I found this page (<- link) most easy readable about operator precedence.
So you could find all of them there.
 
Amie Mac
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Liutauras Vilda wrote:And I found this page (<- link) most easy readable about operator precedence.
So you could find all of them there.


Thanks.

I didn't really think about that assignment being an operator and needing precedence.
 
It is sorta covered in the JavaRanch Style Guide.
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