Cannot implicitly convert type 'object' to 'bool'
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I used to work in a shop (doing just plain C) that had that specified in the coding standards. It made no sense to me, but I went along. One day I was talking with "the guru" (who probably wrote the standard) and he agreed that it was pointless so he didn't enforce it. The basic problem is that it only works when comparing an Lvalue and an Rvalue; many times that is not the case, so you need to think about what you are doing and recognize the situation. And if you can do that, then chances are you won't make that mistake anyway. When it comes right down to it; anyone who is prone to that kind of mistake is also unlikely to remember the rule. By the way... HP C V7.3-009 on OpenVMS Alpha V8.3 says:
JB> cc aa.c /warn=(enable=(check),verbose)
if ( result = 5 )....^
%CC-I-CONTROLASSIGN, In this statement, the assignment expression "result=5" is used as the controlling expression of an if, while o
r for statement.
at line number 13 in file MY$ROOT:[000000]AA.C;3
Description: A common user mistake is to accidentally use assignment operator "=" instead of the equality operator "==" in an expres
sion that controls a transfer. For example saying if (a = b) instead of if (a == b). While using the assignment operator is valid,
it is often not what was intended. When this message is enabled, the compiler will detect these cases at compile-time. This can oft
en avoid long debugging sessions needed to find the bug in the user's program.
User Action: Make sure that the assignment operator is what is expected.if ( 5 = result ).........^
%CC-E-NEEDLVALUE, In this statement, "5" is not an lvalue, but occurs in a context that requires one.
at line number 18 in file MY$ROOT:[000000]AA.C;3
Description: An expression that must be an lvalue was not an lvalue. For example, the operand of the address-of operator must be an
lvalue.
User Action: Modify the expression so that it is an lvalue.Edit:
C:\>cc aa
Borland C++ 5.5 for Win32 Copyright (c) 1993, 2000 Borland
aa.c:
Warning W8060 aa.c 14: Possibly incorrect assignment in function mainC:\>\mingw\bin\gcc -Wall aa.c
aa.c: In function `main':
aa.c:14: warning: suggest parentheses around assignment used as truth valuemodified on Saturday, August 7, 2010 11:40 PM
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I keep getting the below error message when I try and run my code. Error 3 Cannot implicitly convert type 'object' to 'bool'. An explicit conversion exists (are you missing a cast?) When I try run the below code: private void Pause_Click(object sender, RoutedEventArgs e) { if (btnPause.Content = "Pause") <<<<
Personally when performing value comparisons with strings (and many other types) I find I am far less prone to syntax errors if I make myself use the "Equals" method. With strings in particular, it is a good practice to use the static method
String.Equals(string a, string b)
as this eliminates the possibility of a null reference exception. With this in mind, the boolean in your if statement would look like this:
if (String.Equals(btnPause.Content, "Pause"))
"We are men of action; lies do not become us."
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I keep getting the below error message when I try and run my code. Error 3 Cannot implicitly convert type 'object' to 'bool'. An explicit conversion exists (are you missing a cast?) When I try run the below code: private void Pause_Click(object sender, RoutedEventArgs e) { if (btnPause.Content = "Pause") <<<<
you are trying to assign "Pause" to btnPause.content (=) you need the equality comparison operator (==) I dont have a lot of context to what you are doing, but you might want to try refering to sender rather than btnPause in the code.
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I keep getting the below error message when I try and run my code. Error 3 Cannot implicitly convert type 'object' to 'bool'. An explicit conversion exists (are you missing a cast?) When I try run the below code: private void Pause_Click(object sender, RoutedEventArgs e) { if (btnPause.Content = "Pause") <<<<
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I keep getting the below error message when I try and run my code. Error 3 Cannot implicitly convert type 'object' to 'bool'. An explicit conversion exists (are you missing a cast?) When I try run the below code: private void Pause_Click(object sender, RoutedEventArgs e) { if (btnPause.Content = "Pause") <<<<
error in line "if (btnPause.Content = "Pause") " it should be like btnpauser.content == "Pause" hopefully this should fix the error
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it really should say
if() expects a boolean and "btnPause.Content" isn't a boolean nor convertible to one
and it could add
there is an assignment in your expression; did you intend to test for equality? if so use ==
Why can't error messages be very specific, after all the parser is specific when it checks things.
harold aptroot wrote:
I did not vote "bad answer"
Neither did I, although I didn't like it much; the user should not change his habits just because the compiler lacks proper error reporting. The suggestion may be OK for C/C++, but doesn't help much for C# code. :)
Luc Pattyn [Forum Guidelines] [Why QA sucks] [My Articles] Nil Volentibus Arduum
Please use <PRE> tags for code snippets, they preserve indentation, and improve readability.
modified on Saturday, August 7, 2010 10:51 AM
Here's a radical idea: why not throw out the '==' and '===' confusion and make the compiler use the single '=' as either an assignment or a comparative operator depending on the context, like VB does? Oh yeah, because we don't want C# to be like VB with all the stigma associated with such simpleton languages. Sorry, I forgot.
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Here's a radical idea: why not throw out the '==' and '===' confusion and make the compiler use the single '=' as either an assignment or a comparative operator depending on the context, like VB does? Oh yeah, because we don't want C# to be like VB with all the stigma associated with such simpleton languages. Sorry, I forgot.
I don't care much what symbol(s) get used for operators, I started out in Fortran which used
.EQ.for equality testing. However if assignment and equality test operators coincide, some semantics get lost, as ina=b==cversusa=b=c; there is only so much context analysis can do. :)Luc Pattyn [Forum Guidelines] [Why QA sucks] [My Articles] Nil Volentibus Arduum
Please use <PRE> tags for code snippets, they preserve indentation, and improve readability.
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I keep getting the below error message when I try and run my code. Error 3 Cannot implicitly convert type 'object' to 'bool'. An explicit conversion exists (are you missing a cast?) When I try run the below code: private void Pause_Click(object sender, RoutedEventArgs e) { if (btnPause.Content = "Pause") <<<<
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Yes, I saw that once I'd replied. It was the changed subject line that threw me off. Sorry, I'm new in the neighbourhood. :)
Ok, first things first...If this is August 10th, I will gladly eat this post. Why are the messages all dated the 10th? Secondly, being "new in the neighbourhood" sounds like a good reason for everyone to pile on and really "get you" for not plowing through all of the messages!! LOL! :laugh:
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Here's a radical idea: why not throw out the '==' and '===' confusion and make the compiler use the single '=' as either an assignment or a comparative operator depending on the context, like VB does? Oh yeah, because we don't want C# to be like VB with all the stigma associated with such simpleton languages. Sorry, I forgot.
You joke, but there's a lot of truth to that. you need the braces { and the weird 'for' syntax, the ++/-- operators and == for equality. it means it's a real programming language. Microsoft could have solved all of the technical problems without C#, by simply releasing .NET with only VB as the language, and it would simply have been the new version of VB, and the rest of us would be dealing with CString and MFC message maps. But now we get to implement IDispoable!
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I thought it was a good idea, though I could never do that myself.
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Instead of coding:
if (btnPause.Content == "Pause")
try writing it this way round
if ("Pause" == btnPause.Content)
then when you inadvertently miss one of the
=signs the compiler will give you a much more useful message.It's time for a new signature.
Yeugh! That looks too much like C++ for my liking. The alternate compiler error is just as confusing; and the alternate code is more confusing to read. The reason they did things the second way in C++ is because:
if (btnPause->Content = "Pause") // Compiles with no errors or warnings NPNPNP
And:
if ("Pause" = btnPause->Content) // Doesn't compile (error)
We don't need to resort to such language hacks in C#. Please, for the kittens!
He who asks a question is a fool for five minutes. He who does not ask a question remains a fool forever. [Chineese Proverb] Jonathan C Dickinson (C# Software Engineer)
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Here's a radical idea: why not throw out the '==' and '===' confusion and make the compiler use the single '=' as either an assignment or a comparative operator depending on the context, like VB does? Oh yeah, because we don't want C# to be like VB with all the stigma associated with such simpleton languages. Sorry, I forgot.
Nope. Firstly, there is no === in C#. Secondly the 'inconvenience' of == is outweighed by its benefit. For example:
while((line = reader.ReadLine()) != null)
This would be more difficult to read (albeit probably less confusing) without the explicit identity equality operator:
line = reader.ReadLine();
while(line != null)
{line = reader.ReadLine();
}The second block has absolutely no intent locality (keeping the same ideas in the same place in code).
He who asks a question is a fool for five minutes. He who does not ask a question remains a fool forever. [Chineese Proverb] Jonathan C Dickinson (C# Software Engineer)
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Personally when performing value comparisons with strings (and many other types) I find I am far less prone to syntax errors if I make myself use the "Equals" method. With strings in particular, it is a good practice to use the static method
String.Equals(string a, string b)
as this eliminates the possibility of a null reference exception. With this in mind, the boolean in your if statement would look like this:
if (String.Equals(btnPause.Content, "Pause"))
"We are men of action; lies do not become us."
You can't get a NRE using the == operator. The .Net runtime essentially does this:
if (Object.ReferenceEquals(a, null) && Object.ReferenceEquals(b, null)) return true;else if (Object.ReferenceEquals(a, null) || Object.ReferenceEquals(b, null)) return false;
else return a.Equals(b);Unless you override the == operator (in which case you should do this in the header). The String.Equals is better because you would be more inclined to use the StringComparison enum[^] - but that is only the case for Strings.
He who asks a question is a fool for five minutes. He who does not ask a question remains a fool forever. [Chineese Proverb] Jonathan C Dickinson (C# Software Engineer)
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Nope. Firstly, there is no === in C#. Secondly the 'inconvenience' of == is outweighed by its benefit. For example:
while((line = reader.ReadLine()) != null)
This would be more difficult to read (albeit probably less confusing) without the explicit identity equality operator:
line = reader.ReadLine();
while(line != null)
{line = reader.ReadLine();
}The second block has absolutely no intent locality (keeping the same ideas in the same place in code).
He who asks a question is a fool for five minutes. He who does not ask a question remains a fool forever. [Chineese Proverb] Jonathan C Dickinson (C# Software Engineer)
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Jonathan C Dickinson wrote:
This would be more difficult to read (albeit probably less confusing) without the explicit identity equality operator:
Except your example uses the inequality operator. :doh:
It's time for a new signature.
I was talking hypothetically, i.e. if '=' was the identity equality operator; expressions like the one I used wouldn't work.
while((line == reader.ReadLine()) != null) { } // This is what I was talking about.
He who asks a question is a fool for five minutes. He who does not ask a question remains a fool forever. [Chineese Proverb] Jonathan C Dickinson (C# Software Engineer)
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I was talking hypothetically, i.e. if '=' was the identity equality operator; expressions like the one I used wouldn't work.
while((line == reader.ReadLine()) != null) { } // This is what I was talking about.
He who asks a question is a fool for five minutes. He who does not ask a question remains a fool forever. [Chineese Proverb] Jonathan C Dickinson (C# Software Engineer)
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Jonathan C Dickinson wrote:
if '=' was the identity equality operator; expressions like the one I used wouldn't work.
I don't see that that follows, since the compiler would still recognise
!=as the not equals operator.It's time for a new signature.
Hurm... The example doesn't need a
==operator because it is demonstrating what is possible when a=and a==are distinct. With==around;=becomes more versatile. Because=is more versatile the example I gave is possible. If there was only=(and no==) the example I gave simply wouldn't work (you would get an warning saying that a boolean is never null). I think the mathematical term for this kind of 'proof' is proof by contradiction. The compiler would recognize!=as the not equals operator, BUT it would recognize the=as identity equality and not assignment. Thus the AST would look (where the VB-route is taken) something like this:WHILESTMT(BOOLEXPR(BOOLEXPR("line", Operator.IdentityEquality, "reader.ReadLine"), Operator.IdentityInequality, NULL))As opposed to (and why my example works):WHILESTMT(BOOLEXPR(BOOLEXPR("line", **_Operator.Assign_**, "reader.ReadLine"), Operator.IdentityInequality, NULL))More simply, the following expression results in a boolean type (and boolean value) in VB:a = bIn C# is results in the type of 'a' (and the value contained by 'a'). Which is why these statements are possible:int0 = int1 = int2 = int3 = int4 = 0; // Set all to 0.He who asks a question is a fool for five minutes. He who does not ask a question remains a fool forever. [Chineese Proverb] Jonathan C Dickinson (C# Software Engineer)
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Hurm... The example doesn't need a
==operator because it is demonstrating what is possible when a=and a==are distinct. With==around;=becomes more versatile. Because=is more versatile the example I gave is possible. If there was only=(and no==) the example I gave simply wouldn't work (you would get an warning saying that a boolean is never null). I think the mathematical term for this kind of 'proof' is proof by contradiction. The compiler would recognize!=as the not equals operator, BUT it would recognize the=as identity equality and not assignment. Thus the AST would look (where the VB-route is taken) something like this:WHILESTMT(BOOLEXPR(BOOLEXPR("line", Operator.IdentityEquality, "reader.ReadLine"), Operator.IdentityInequality, NULL))As opposed to (and why my example works):WHILESTMT(BOOLEXPR(BOOLEXPR("line", **_Operator.Assign_**, "reader.ReadLine"), Operator.IdentityInequality, NULL))More simply, the following expression results in a boolean type (and boolean value) in VB:a = bIn C# is results in the type of 'a' (and the value contained by 'a'). Which is why these statements are possible:int0 = int1 = int2 = int3 = int4 = 0; // Set all to 0.He who asks a question is a fool for five minutes. He who does not ask a question remains a fool forever. [Chineese Proverb] Jonathan C Dickinson (C# Software Engineer)
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You can't get a NRE using the == operator. The .Net runtime essentially does this:
if (Object.ReferenceEquals(a, null) && Object.ReferenceEquals(b, null)) return true;else if (Object.ReferenceEquals(a, null) || Object.ReferenceEquals(b, null)) return false;
else return a.Equals(b);Unless you override the == operator (in which case you should do this in the header). The String.Equals is better because you would be more inclined to use the StringComparison enum[^] - but that is only the case for Strings.
He who asks a question is a fool for five minutes. He who does not ask a question remains a fool forever. [Chineese Proverb] Jonathan C Dickinson (C# Software Engineer)
Jonathan, I can see why my language may have been confusing. I was not meaning to imply that using the == operator would result in a NullReferenceException. My first statement was that the "Equals" method should be used to make the comparison, and I then went on to state that the static method should be preferred for strings (rather than the instance method) since using the instance method could result in a NullReferenceException while using the static method will not. Looking back at my post, however, I can see why one might think I was implying something different, which was not my intent. Regardless, thanks.
"We are men of action; lies do not become us."