int or bool?

[Fred]

Why was the bool type introduced into c++?
What does it provide that int does not and are the two entirely
interchangable in conditional expressions?

Thanks
Fred

[Chris Jefferson]

Fred wrote:

Why was the bool type introduced into c++?
What does it provide that int does not and are the two entirely
interchangable in conditional expressions?

First of all, I like bool because it lets me say what I mean. If I want
a function to return a "true" or "false" value, I make it return bool,
because that is exactly what I mean.

They are totally interchangable, because 1!=-1, but bool(1)==bool(-1).
Bools can in many ways be considered "almost the same as" ints where you
are only allowed 0 or 1, but they impose this condition for you rather
than forcing you to make sure you apply it yourself.

You can of course write functions and templates which behave differently
depending on which one they are given, but of course this is true for
all types.

Chris

[Ivan Vecerina]

"Fred" <Fr**@somewhere .abc> wrote in message
news:cp******** **@titan.btinte rnet.com...

Why was the bool type introduced into c++? See for example:
http://www.gotw.ca/gotw/026.htm
What does it provide that int does not and are the two entirely
interchangable in conditional expressions?

bool only has two possible values/states: true and false.

Expressions such as a != b have a different meaning
for bool than for int.
When a and b are of bool type, it is equivalent to a logical x-or.

One should use bool whenever a value can only be true or false,
just as one should use int rather than double as it helps avoid
bugs.

hth,
Ivan
--
http://ivan.vecerina.com/contact/?subject=NG_POST <- email contact form
Brainbench MVP for C++ <> http://www.brainbench.com

[Andrew Koenig]

"Fred" <Fr**@somewhere .abc> wrote in message
news:cp******** **@titan.btinte rnet.com...

Why was the bool type introduced into c++?
Because the practice of defining one's own synonym for int and using it as a
boolean type had grown to the point where large systems typically had
multiple incompatible definitions of boolean types.
What does it provide that int does not and are the two entirely
interchangable in conditional expressions?

They are not interchangeable . For one thing, if int and bool are different
types, you can overload on them.

[Dave O'Hearn]

Fred wrote:

Why was the bool type introduced into c++?
What does it provide that int does not and are the two
entirely interchangable in conditional expressions?

It was introduced because lots of code was creating its own bool types
and they were incompatible with each other. When done with macros, this
creates problems if two libraries try to define TRUE differently. With
enums in the global scope, it will fail to compile. Also, not everyone
made their "true" convertable to 1 like the standard does. Someone
might define "true" as -1, and then two different concepts of "true"
would compare unequal.

--
Dave O'Hearn

[jeffc]

"Fred" <Fr**@somewhere .abc> wrote in message
news:cp******** **@titan.btinte rnet.com...

Why was the bool type introduced into c++?
What does it provide that int does not and are the two entirely
interchangable in conditional expressions?

Using a number to represent a boolean was a hack to get around the fact that
there was no boolean. Kind of like using char* because there was no String
class.

[jeffc]

"Andrew Koenig" <ar*@acm.org> wrote in message
news:zd******** **************@ bgtnsc04-news.ops.worldn et.att.net...

"Fred" <Fr**@somewhere .abc> wrote in message
news:cp******** **@titan.btinte rnet.com...

Why was the bool type introduced into c++?

Because the practice of defining one's own synonym for int and using it as a
boolean type had grown to the point where large systems typically had
multiple incompatible definitions of boolean types.

Not to mention the fact that it required work to define and make available such
a basic type to begin with.

[Howard]

One should use bool whenever a value can only be true or false,
ok
just as one should use int rather than double as it helps avoid
bugs.

what? I'd think one should use int when integers are required, and double
when floating-point numbers are required (and when the float type is not
otherwise required for whatever reason). What does this have to do with
avoiding bugs?

-Howard

[Olivier Azeau]

Howard wrote:

One should use bool whenever a value can only be true or false,

ok

just as one should use int rather than double as it helps avoid
bugs.

what? I'd think one should use int when integers are required, and double
when floating-point numbers are required (and when the float type is not
otherwise required for whatever reason). What does this have to do with
avoiding bugs?

-Howard

Saying you can use an int to store a boolean value is like saying you
can use a double to store an int : you can do it but you can get a bug
for example if you store multiple values of the "bigger" set to
represent a single value of the "smaller" set.

bool a = true, b = true;
if( a && b )
assert( a == b ); // true

int a = -1, b = 1;
if( a && b )
assert( a == b ); // false

[Vinodh Kumar P]

"Chris Jefferson" <ca*@cs.york.ac .uk> wrote in message
news:41******** ******@cs.york. ac.uk...

Fred wrote:

Why was the bool type introduced into c++?
What does it provide that int does not and are the two entirely
interchangable in conditional expressions?

First of all, I like bool because it lets me say what I mean. If I want
a function to return a "true" or "false" value, I make it return bool,
because that is exactly what I mean.

They are totally interchangable, because 1!=-1, but bool(1)==bool(-1).

TCPPPL says nonzero integers convert to true and 0 converts to false.
Why all nonzero integers including negative integers should convert to zero?
Converting negative integers to false is as natural as converting 0 to
false?