While statement with multiple conditions - c#

I have the following while statement -
while ((!testString.Contains("hello")) && (NewCount != OldCount) && (attemptCount < 100))
{
//do stuff (steps out too early)
}
This is stepping out of the statement even though all the conditions have not been met.
I have tried to reduce it like -
while (!testString.Contains("hello"))
{
// this works and steps out when it should
}
And this steps out when hello is present for example. I also tried changing this to an OR statement which reversed the problem to never stepping out the statement.
Addint the && (NewCount != OldCount) && (attemptCount < 100)) conditions is causing this behaviour how can I resolve this?

This is stepping out of the statement even though all the conditions
have not been met.
To achieve that you need to specify logical OR (||).
For example:
while ((!testString.Contains("hello")) || (NewCount != OldCount) || (attemptCount < 100))
{
//while at least one those conditions is true, loop will work
}
Which means that inside loop you need to introduce security checks, where required, for conditions which are not more true, while loop is still executing.

As an addition to TigranĀ“s answer. Often (in order to avoid mess with the complex condition) it could be useful to push the condition into the loop:
while (true) { // loop forever unless:
if (testString.Contains("hello")) // ...test string contains "hello"
break;
if (NewCount == OldCount) // ...counts are equal
break;
if (attemptCount >= 100) // ... too many attempts
break;
// ...it's easy to add conditions (as well as comment them out) when you have them
// Loop body
}

Related

Forcing SWITCH to process all statements or break if case match [StateMachine]

Let's say I need to go through bunch of statements and process each case, results of which will be "incrementation" of IntVar. So like:
int result = 1;
if (condition1)
{
result = result + 2;
}
if (condition2)
{
result++;
}
if (condition3)
{
result++;
}
//things get hairy
if (result != 5 && condition4)
{
result++;
}
if (result != 5 && condition5)
{
result++;
}
// do a thing based on a result value
I' love to use while{} here but I can't because result can be less than 5 when all cases processed. What i had in mind is putting all the checks into SWITCH and make continue to process them until the end (and then continue code normally) UNLESS result hits "5" middle way, then just go straight to result process.
Is it possible to force default SWITCH to do so without writing custom one and/or overcomplicating things too much?

C# Error Additional information: The enumeration has already completed

This is my first time using the enumerator interface.
I am Trying to look threw a stack to find next occurrence of a string.
The loop is suppose to loop threw my tags stack and find out if a tag inside my stack is a tag i was looking for. Once the stack gets to the last tag in the stack it crashes and issues the error in the title. The last tag in the list also happens to be the first match for lookforthisTag string variable. I want the while look to exit when the if statement finds a match or when all stack items have been compared.
/*find next opening tag in stack */
int I = 1;
var enumerator = tags.GetEnumerator(); /// create a enumerator variable
/// move to the next tag in stack
while ( enumerator.MoveNext() != false || found == true || I <= countofTags)
{
htmlTags currentTag = enumerator.Current; // this line causes error.
if (currentTag.open_tag == lookforthisTag)
{
found = true;
}
I++;
}///End while.
This line
while ( enumerator.MoveNext() != false || found == true || I <= countofTags)
will execute the following logic
Does the enumerator returns true? If yes enter the loop else check
next condtion
Is found == true? If yes enter the loop, else check the next condition
Is I <= countofTags? If yes enter the loop, else exit the loop
As you can see even when the enumerator return false it enters the loop because at that point found is true, but inside the loop you call enumerator.Current and this triggers the error message.
Probably you want
while ( !found && enumerator.MoveNext() && I <= countofTags)
Consider that a normal foreach loop would do the same
htmlTags found = null;
foreach(htmlTags currentTag in tags)
{
if (currentTag.open_tag == lookforthisTag)
{
found = currentTag;
break;
}
}
if(found != null)
{
// got it...
}
or just using Linq
htmlTags found = tags.FirstOrDefault(x => x.open_tag == lookforthisTag)
if(found != null)
{
// you have found your tag.
}
I want also to mention the fact that your I <= countOfTags logic
doesn't seem to have any utility in the code shown. The variable I will be always equal to the countOfTags (or just simply equal to tags.Count) because you don't break the loop and continue till the end of the enumeration. If you want to know the 'position' of the found tag, just increment it.
I would rewrite your while condition like this:
while ( enumerator.MoveNext() && !found && I < countofTags)
Or just use linq:
tags.Single (currentTag == currentTag.open_tag == lookforthisTag)
The condition in the while will be true even if enumerator.MoveNext() will be false, because of the or conditions.
It can probably be fixed with changing the condition and also using break to get out of the loop.
like this:
while ( enumerator.MoveNext() && I <= countofTags)
{
htmlTags currentTag = enumerator.Current; // this line causes error.
if (currentTag.open_tag == lookforthisTag)
{
found = true;
break;
}
I++;
}///End while.
But, i wouldn't go this way in the first place.
Use LINQ:
var myItem = tags.FirstOrDefault(currentTag=> currentTag.open_tag == lookforthisTag);

assigning value to bool inside while loop

I know this is a very newbie C# question but I am implementing a small program which does the following:
namespace ConsoleApplication
{
class Program
{
static void Main(string[] args)
{
bool isRun = false;
int number = 0;
while (isRun = (true) && number < 3)
{
++number;
Console.WriteLine("Number = {0}", number.ToString());
Console.WriteLine();
}
Console.WriteLine(isRun.ToString());
Console.ReadLine();
}
}
}
At the end of the while loop, I would have expected the bool value to be true, but is is printed to be false. Why is that? Is this different from C++ where I would have done something like and the same thing in C# is giving me false
while(number<3)
{
is = true;
}
if(is){
cout<<true;
}
The reason you're seeing this behavior is due to the operator precedence involved. Here the && binds more strongly than = so the code in the loop is actually bound as the following
while (isRun = (true && number < 3)) {
...
}
Once number > 3 the && expression is false and is assigned into the isRun value and simultaneously terminates the loop. Hence once the loop exits you will see isRun as false
To get the behavior you are looking for you will need to manually correct the precedence with parens.
while ((isRun = (true)) && number < 3) {
...
}
Note: In general, as #Servey pointed out, the assignment of locals to expressions inside the loop predicate is considered bad practice. Many C# users would actually be surprised that code compiles at all because they've been conditioned to only use == in loops.
It's more idiomatic to simply set isRun to true on the first line of the loop for this pattern.
while (number < 3) {
isRun = true;
...
}
The problem is that you have set you boolean variable to false and without assigning it back to true, in while loop you are matching it against the value true, thus it fails in every case.

Can this statement ever evaluate to FALSE?

I stumbled upon this while doing a review and the author is not available:
int n = Convert.ToInt32(text);
if (((n > 0) || (n < 0)) || (n == 0))
{
return 1;
}
The code in general looks solid and it's hard for me to believe that the only purpose of this snippet is to confuse reviewers, but I don't see a way for this condition to fail. Am I missing something?
This may be a remnant of a nullable type. See here at msdn for an explanation, but basically if your code was originally this:
int? n = StringToInt(text); // People roll their own functions to do this, though
// they really shouldn't
if (((n > 0) || (n < 0)) || (n == 0))
{
return 1;
}
Then this could possibly fall through. Each of the statements above would be false, as n could be null from the function, assuming it returned null on a bad input, and the code supported nullable types.
Unlikely, but when looking at "maintained code" anything is possible. But as written, it MUST return 1 (or throw an exception, as mentioned by others in this thread).
It will always return true, assuming it gets there.
Consider:
bool x = (n > 0) || (n < 0);
bool y = (n == 0);
if (x || y)
{
return 1;
}
If n is not zero then either n > 0 or n < 0 is true, so x is true and y is false.
If n is zero, n == 0 is true, so x is false and y is true.
Either way, one side of the OR is true.
That sure looks like a 100% true statement to me. All those parentheses shouldn't matter in the least, since || is associative, i.e.,
(a || b) || c == a || (b || c) == a || b || c
If you overload the relational operators for your class, it might be the case that the condition evaluates to false, but since n is an int, it always evaluates to true
It's possible that int n = Convert.ToInt32(text); could throw an exception, in which case the if statement never even gets evaluated.
See Convert.ToInt32() on MSDN.
As above, it will always be true because, by definition, any real number is either zero, less than zero or greater than zero, and you have covered all cases in your code.
Always will be 1, unless Convert.ToInt32(text) throws an exception.
I don't see how it can evaluate to false.
If, however, n was declared at a different scope where more than a single thread had access to it and one of these threads changes its value, theres quite a high chance the condition would fail.
it will always be true as you write all the states it might be (e.g < > ==)
Yes, it could also throw an exception if the conversion fails :-)

Are variables shared in recursive functions

I'm trying to calculate the number of success cases within a recursive function in C#, but I'm astonished by the fact that my variable is shared between all the function calls!
[update 2]
More than strange this time. doing so
i = i + validTreesFun(tree.Nodes, newWords.ToList()) ;
resets i to 0
doing this
i = validTreesFun(tree.Nodes, newWords.ToList()) + i ;
gives some results (I'm not sure if it's correct)
[updated : the full code]
public static int validTreesFun(List<Tree<char>> nodes, List<string> words)
{
int i = 0;
if (nodes == null && (words == null || words.Count == 0 || (words.Count == 1 && words.First() == "")))
return 1;
else
if (nodes == null)
return 0;
foreach (Tree<char> tree in nodes)
{
var validWords = words.Where(w => w.ToCharArray()[0] == tree.Root)
.Select(w => w);
if (validWords.Count() == 0)
return 0;
else
{
var newWords = validWords.Select(w => join( w.ToCharArray().Skip(1).ToArray()));
i += validTreesFun(tree.Nodes, newWords.ToList());
}
}
return i;
}
when debuging the variable i take the value 1 but it resets to 0 on the next iteration!!
despite the use of
i = i + ....
What is the problem in that piece of code?
Thank you
if (validWords.Count() == 0)
return 0;
Should be
if (validWords.Count() == 0)
continue;
Also, in general, I personally think it is nicer looking to only send in one element at a time to a recursive function.
public static int validTreesFun(Tree<char> node, List<string> words)
That way you don't get the same kind of mistake like above. Finally, a minor note.
w => w.ToCharArray()[0] == tree.Root
can be written as
w => w[0] = tree.Root
No local variables are not at all shared between recursive calls, you should consider some other design problem, inside and after your foreach loop, I dont see any return statements, can you post full code.
Ok, in debugging you will always observe i's current method's value, debugging is not good in recursive functions, its little hard to understand, you will have to move your control down in Call Stack in order to actually observe value of earlier caller of current function.
I would advice you to output Trace or on log file with your level of node, that will help you actual debugging.
Please use TRACE Statement as follow..
Trace.WriteLine(string.Format("{0},{1}",tree.Name,i));
Local variables are not being shared.
What you are seeing (the reset to 0) is the value of i in the (recursively) called function validTreesFun (i gets set to 0 at the start of the function).
Just looking at your code, I think a possible bug might be in someTestHere - if that is never true, then i will stay 0 in the outer scope. Otherwise it should increment by 1 for each true test.
When you are in debug mode, you indeed see that the i is reseted for the call but remain to the wanted value for the caller. Eg , the stack :
validTreesFun --i = 0 for this one
validTreesFun --i = x for this one, but if you do not go trow the calling stack, you will see 0, which is the good value for the top of the stack

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