Control cannot fall through from one case to another?
-
I need to convert these C++ code into C# code . What's is the easiest way ? thanks state=1 switch (state) { case 1: //do something state++; case 2: //do something if ( ) { state++; } else { state=state+5; } break; case 3: //do something state++; ............ case 100: break; }
Firstly, find the programmer who originally wrote this. Take him outside, and beat him senseless. It's pretty bad code as C++, and can't be directly translated into C# as the later enforces rules to prevent accidental mistakes (such as fall through of cases). Secondly, get out a pen and paper and do a flow diagram of some sort to work out how this spagetti works. Tidy the diagram up so it can be reliably implemented in any language. Re-code into C#. Not a quick job by any means, but it's the companies' (or whoevers') fault for allowing such rubbish to be produced in the first place!
No trees were harmed in the sending of this message; however, a significant number of electrons were slightly inconvenienced. This message is made of fully recyclable Zeros and Ones
-
hi I have these code . What could cause above error ? Thanks state=1 switch (state) { case 1: //do something goto case 2; case 2: //do something goto case 3; case 3: //do something goto case 4; ............ case 100: //do something }
Oh, dear
- Never use goto. It kills babies
- You just drop though each case. Why?
- You do a switch, when you've just set the variable you switch on
- You have one hundred hard-coded cases. Find out how to make that dynamic
- The switch is unnecessary. If you're just dropping through, then it won't make any difference
- You have basically implemented line labels. Why do you have line labels, when you can refactor your code
- No default: option
- The first line of is missing a semicolon
-
Oh, dear
- Never use goto. It kills babies
- You just drop though each case. Why?
- You do a switch, when you've just set the variable you switch on
- You have one hundred hard-coded cases. Find out how to make that dynamic
- The switch is unnecessary. If you're just dropping through, then it won't make any difference
- You have basically implemented line labels. Why do you have line labels, when you can refactor your code
- No default: option
- The first line of is missing a semicolon
Computafreak wrote:
You just drop though each case. Why?
This is a state-machine with a selectable first state. If C# had a "computed goto" (as Fortran has) then the switch would not be necessary. :)
Luc Pattyn [Forum Guidelines] [My Articles]
The quality and detail of your question reflects on the effectiveness of the help you are likely to get. Show formatted code inside PRE tags, and give clear symptoms when describing a problem.
-
OriginalGriff wrote:
Don't use goto unless you really, really have to
Fixed that for you :)
Never underestimate the power of human stupidity RAH
There are times when a goto can really improve readability, rather than if...if..if..if... etc. Having said that, I don't think I've used one in a non-assembler language for twenty or so years.
No trees were harmed in the sending of this message; however, a significant number of electrons were slightly inconvenienced. This message is made of fully recyclable Zeros and Ones
-
There are times when a goto can really improve readability, rather than if...if..if..if... etc. Having said that, I don't think I've used one in a non-assembler language for twenty or so years.
No trees were harmed in the sending of this message; however, a significant number of electrons were slightly inconvenienced. This message is made of fully recyclable Zeros and Ones
If you're a student/junior dev though; the rule is NEVER. You're not experienced enough to ID the few cases where it really is the best choice and will just learn bad habits.
It is a truth universally acknowledged that a zombie in possession of brains must be in want of more brains. -- Pride and Prejudice and Zombies
-
Computafreak wrote:
You just drop though each case. Why?
This is a state-machine with a selectable first state. If C# had a "computed goto" (as Fortran has) then the switch would not be necessary. :)
Luc Pattyn [Forum Guidelines] [My Articles]
The quality and detail of your question reflects on the effectiveness of the help you are likely to get. Show formatted code inside PRE tags, and give clear symptoms when describing a problem.
Luc Pattyn wrote:
If C# had a "computed goto"
I'd have stuck with C++. :laugh:
No trees were harmed in the sending of this message; however, a significant number of electrons were slightly inconvenienced. This message is made of fully recyclable Zeros and Ones
-
I need to convert these C++ code into C# code . What's is the easiest way ? thanks state=1 switch (state) { case 1: //do something state++; case 2: //do something if ( ) { state++; } else { state=state+5; } break; case 3: //do something state++; ............ case 100: break; }
Why use a case at all, it seems pretty procedural to me. You want to execute a block of code in order, your condition isn't really needed since you always increment 'state', so your select case is useless.
-
If you're a student/junior dev though; the rule is NEVER. You're not experienced enough to ID the few cases where it really is the best choice and will just learn bad habits.
It is a truth universally acknowledged that a zombie in possession of brains must be in want of more brains. -- Pride and Prejudice and Zombies
-
If you're a student/junior dev though; the rule is NEVER. You're not experienced enough to ID the few cases where it really is the best choice and will just learn bad habits.
It is a truth universally acknowledged that a zombie in possession of brains must be in want of more brains. -- Pride and Prejudice and Zombies
Then how do you execute multiple cases in a switch in C#?
-
hi I have these code . What could cause above error ? Thanks state=1 switch (state) { case 1: //do something goto case 2; case 2: //do something goto case 3; case 3: //do something goto case 4; ............ case 100: //do something }
I wrote this code to test: int i=int.Parse(Console.ReadLine()); switch(i) { case 0: Console.WriteLine(0); goto case 1; case 1: Console.WriteLine(1); break; } This works. If you don't do the goto case 1 you will receive an error, and if you don't do the break at case 1 you will also receive an error. I think the problem with your code is the lack of some "goto case x" or some "break". --- I don't like such gotos, but if that the best way, try finding the lacking gotos / breaks.
modified on Wednesday, May 13, 2009 10:06 AM
-
Computafreak wrote:
You just drop though each case. Why?
This is a state-machine with a selectable first state. If C# had a "computed goto" (as Fortran has) then the switch would not be necessary. :)
Luc Pattyn [Forum Guidelines] [My Articles]
The quality and detail of your question reflects on the effectiveness of the help you are likely to get. Show formatted code inside PRE tags, and give clear symptoms when describing a problem.
Luc Pattyn wrote:
state-machine
I prefer to put the
switchin awhile, rather than use fall-through for that. -
dan neely wrote:
the rule is NEVER
Absolutly true... Learn the law! Obey the law! Fear the law! Believe the law! And THEN you can break the law!
Panic, Chaos, Destruction. My work here is done.
williamnw wrote:
Learn the law! Obey the law! Fear the law! Believe the law!
**
Judge Dredd wrote:
I am the law!!
**
No trees were harmed in the sending of this message; however, a significant number of electrons were slightly inconvenienced. This message is made of fully recyclable Zeros and Ones
-
I wrote this code to test: int i=int.Parse(Console.ReadLine()); switch(i) { case 0: Console.WriteLine(0); goto case 1; case 1: Console.WriteLine(1); break; } This works. If you don't do the goto case 1 you will receive an error, and if you don't do the break at case 1 you will also receive an error. I think the problem with your code is the lack of some "goto case x" or some "break". --- I don't like such gotos, but if that the best way, try finding the lacking gotos / breaks.
modified on Wednesday, May 13, 2009 10:06 AM
But remember that the goto in this case is fixed. If you need something like: switch(x) { case 0: if (someCondition) x += 5; else x += 6 do other processing, and then continue with the next case for X (that can be 5, 6 or some other value) the best solution will be to use a while. For example: bool continueRunning = true; while (continueRunning) { switch(x) { case 0: // do something; if (someCondition) x += 5; else x += 6; break; ... other cases ... default: continueRunning = false; break; } } So, this will: Execute the switch with x being zero. You can then recalculate x, and it will execute the switch again. You can do that how many times you want. If you want to stop it, you call continueRunning = false; And, if the value does not fall in any case, it will enter the default, with will set continueRunning to false and stops the block.
modified on Wednesday, May 13, 2009 10:07 AM
-
I wrote this code to test: int i=int.Parse(Console.ReadLine()); switch(i) { case 0: Console.WriteLine(0); goto case 1; case 1: Console.WriteLine(1); break; } This works. If you don't do the goto case 1 you will receive an error, and if you don't do the break at case 1 you will also receive an error. I think the problem with your code is the lack of some "goto case x" or some "break". --- I don't like such gotos, but if that the best way, try finding the lacking gotos / breaks.
modified on Wednesday, May 13, 2009 10:06 AM
Paulo Zemek wrote:
This works.
Yes. So does this:
Console.WriteLine(0);
Console.WriteLine(1);Same outcome, more readable though. :)
Luc Pattyn [Forum Guidelines] [My Articles]
The quality and detail of your question reflects on the effectiveness of the help you are likely to get. Show formatted code inside PRE tags, and give clear symptoms when describing a problem.
-
Paulo Zemek wrote:
This works.
Yes. So does this:
Console.WriteLine(0);
Console.WriteLine(1);Same outcome, more readable though. :)
Luc Pattyn [Forum Guidelines] [My Articles]
The quality and detail of your question reflects on the effectiveness of the help you are likely to get. Show formatted code inside PRE tags, and give clear symptoms when describing a problem.
This does not generate the same result. I set the i = 0. But consider that i is entered by the user. Console.WriteLine(0); Console.WriteLine(1); will not be the same, as in some cases only the case 1 must be executed. As I understand, the idea is to have the option to "start at any point", but continue from it. And I am not saying the solution used is a good one, but it is the easiest to convert a C++ code without really refactoring it.
-
Then how do you execute multiple cases in a switch in C#?
LalalalaICantHearYouLalalalalala Outside of a single school exercise (Generate the complete lyrics for the 12 days of Christmas) I can't think of a single case where falling through was desired behavior. Seriously though, that's the exception which proves the rule. :-D
It is a truth universally acknowledged that a zombie in possession of brains must be in want of more brains. -- Pride and Prejudice and Zombies
-
LalalalaICantHearYouLalalalalala Outside of a single school exercise (Generate the complete lyrics for the 12 days of Christmas) I can't think of a single case where falling through was desired behavior. Seriously though, that's the exception which proves the rule. :-D
It is a truth universally acknowledged that a zombie in possession of brains must be in want of more brains. -- Pride and Prejudice and Zombies
dan neely wrote:
Outside of a single school exercise (Generate the complete lyrics for the 12 days of Christmas) I can't think of a single case where falling through was desired behavior.
It does happen occasionally. My current project has two switches where it was much clearer to add a "goto" rather than convoluted logic. The important thing, of course, is to comment it properly so everyone can see exactly what's being done, and why.
There are three kinds of people in the world - those who can count and those who can't...
-
Computafreak wrote:
You just drop though each case. Why?
This is a state-machine with a selectable first state. If C# had a "computed goto" (as Fortran has) then the switch would not be necessary. :)
Luc Pattyn [Forum Guidelines] [My Articles]
The quality and detail of your question reflects on the effectiveness of the help you are likely to get. Show formatted code inside PRE tags, and give clear symptoms when describing a problem.
Luc Pattyn wrote:
This is a state-machine with a selectable first state. If C# had a "computed goto" (as Fortran has) then the switch would not be necessary.
Or do the state machine as a "while...switch..." loop, and set the initial state before entry. That's how I've always done it (and I do go back to the old Fortran days as well :)).
There are three kinds of people in the world - those who can count and those who can't...
-
Why use a case at all, it seems pretty procedural to me. You want to execute a block of code in order, your condition isn't really needed since you always increment 'state', so your select case is useless.
I'm back. It depends on what
stateis equal to. As I have understood, thestate=1line is just an example of possible value which can takestate. Ifstatewould be fixed to 1 every time, 80% of could be removed, including the wholeswitchstatement. So the question to dec82: Isstate=1line just an example or is it actually present in the source code?Greetings - Jacek Gajek
-
LalalalaICantHearYouLalalalalala Outside of a single school exercise (Generate the complete lyrics for the 12 days of Christmas) I can't think of a single case where falling through was desired behavior. Seriously though, that's the exception which proves the rule. :-D
It is a truth universally acknowledged that a zombie in possession of brains must be in want of more brains. -- Pride and Prejudice and Zombies
I agree that fall-through is evil, but there are still situations where you want to execute multiple cases; if not with goto, then some other keyword, at least the goto acts as a cry for help.
