Boolean in C

sierdzio

bool is a built-in type in C, you don't have to implement anything.

SaintBroseph

Yes Yes! I actually wanted an example of a C boolean using typedef keyword.

JonB

typedef enum { false, true } mybool;

if that's the sort of thing your teacher wants from you, to show you understand?

sierdzio

typedef bool boolean;

JonB

@sierdzio

#typedef bool boolean

What is #typedef in C/C++? ;-)

sierdzio

Good point :D Corrected

DarkChocolateMuffinz

@SaintBroseph Here's an example (code) of C boolean using typedef

#include <stdio.h>

// creating custom data type bool
typedef enum {false, true} bool_enum;
int main() {
    bool_enum x=false; // declaration and initialization  
    if(x==true)  // conditional statements    
        printf("The value of x is true");  
    else  
        printf("The value of x is false");
  
    return 0;  
    // Output: The value of x is false
}

Source: [EDIT: Link removed --JKSH]

Ketan__Patel__0011

typedef bool boolean;
int main()
{
     boolean A = false;
     if (A == false) printf("MESSAGE")
     else  printf("MESSAGE")

     return 0;
}

if your problem is solved then please close the thread

Kent-Dorfman

comparing a boolean to true or false is redundant. Conditional expressions return a boolean (in C, 0 or not 0) so X or !X is adequate.

Also, bool is a C99 thing via <stdbool.h>. Much C legacy still exists where there is no real boolean type but instead zero or not zero logic.

kshegunov

@Kent-Dorfman said in Boolean in C:

comparing a boolean to true or false is redundant.

Not to mention wrong, generally speaking. 1 evaluates to true but so does -1, so comparing against true is simply the way to break it. Enums implicitly decay to the underlying type so checking against condition and !condition is the correct way to do it, even if a typedef is used.

sierdzio

I find it much easier to understand if something is false when I see if (something == false) than when I see if (!something). Especially in longer expressions it is very easy to miss a single character like ! and read the code wrong.

JonB

@sierdzio
I see a personal-choice-disagreement debate looming... ;-)

I do agree it is "unfortunate" that C chose just that little ! for "not". But personally I never write == false or != false, because I would never "say" that in RL....

J.Hilk

@sierdzio , @JonB

are you guys aware, that not is a valid keyword in c++ ?

https://en.cppreference.com/w/cpp/keyword/not

JonB

@J-Hilk
Yup. And it's devil's-spawn! ;-) [Same for and & or. If I wanted to program in Python or Pascal I would have picked that.] I would never use that, as "nobody" (most people) else uses it or knows about it, so I would regard it as an anti-pattern!

sierdzio

@J-Hilk said in Boolean in C:

@sierdzio , @JonB

are you guys aware, that not is a valid keyword in c++ ?

https://en.cppreference.com/w/cpp/keyword/not

Yes but not in all compilers :-( MSVC does not recognize it.

JonB

@sierdzio
Good, but are you sure? Since it is valid since C99, I would have thought that MSVC would accept those?

sierdzio

@JonB said in Boolean in C:

@sierdzio
Good, but are you sure? Since it is valid since C99, I would have thought that MSVC would accept those?

Last time I tried was last year. Clang, GCC all are 100% fine with it, MSVC was throwing errors.

I now see it's supposed to be defined in some iso646.h header, I never included it, perhaps that's the reason.

J.Hilk

@sierdzio said in Boolean in C:

Yes but not in all compilers :-( MSVC does not recognize it.

VS been nonconforming! 😱 Color me surprised 😉

JonB

@sierdzio
If one has to include a header file for them, makes me wonder if they are not "part of the language", just should be available if you include the header. Are they just #defines in that file??

sierdzio

@JonB said in Boolean in C:

@sierdzio
If one has to include a header file for them, makes me wonder if they are not "part of the language", just should be available if you include the header. Are they just #defines in that file??

yup :D

#define and    &&
#define and_eq &=
#define bitand &
#define bitor  |
#define compl  ~
#define not    !
#define not_eq !=
#define or     ||
#define or_eq  |=
#define xor    ^
#define xor_eq ^=

They are not actual C++ language reserved keywords.