Newbie Questions on If statement

[Yue]

Hi, all,

I know this is too simple...but can somebody tell me:


any expression other than "0" is of boolean "true" type


so: if (x) {} is equivalent to if(x != 0) (1. it has to be a "true"
boolean within if bracket?)


2. if I want the expression to return false in the if bracket, I just
need to write a single "0" or "x=0"


Thanks very much!


yue

 

[Daniel T.]

I know this is too simple...but can somebody tell me:

any expression other than "0" is of boolean "true" type

so: if (x) {} is equivalent to if(x != 0) (1. it has to be a "true"
boolean within if bracket?)

2. if I want the expression to return false in the if bracket, I just
need to write a single "0" or "x=0"

If I understand you correctly, you understand the if statement.

However, you generally don't want to do assignments inside the
expression of an 'if' statement. Things can get pretty muddled pretty
fast that way.

 

[Ron Natalie]

so: if (x) {} is equivalent to if(x != 0) (1. it has to be a "true"
boolean within if bracket?)

Yes provided x isn't some odd type that has overloads for != that do
nonobvious things.

2. if I want the expression to return false in the if bracket, I just
need to write a single "0" or "x=0"

if(0) and if(false) mean the same thing.
if(x=0) will evaluate to false, but has the side effect of setting x
to zero as well.

if(x==0) is the moral equivelent of writing if(!x) (again it can be
thwarted by classes that overload == or ! in non obvious ways).

 

[Dave Rahardja]

so: if (x) {} is equivalent to if(x != 0) (1. it has to be a "true"
boolean within if bracket?)

For POD types, yes. For user-defined types (classes), generally, no.

-dr

 

[Rahul]

For POD types, yes. For user-defined types (classes), generally, no.

-dr

user-defined types would work if they have an operator function, which
converts the user-defined type to a bool type...

 

[Yue]

if(x==0) is the moral equivelent of writing if(!x)  (again it can be
thwarted by classes that overload == or ! in non obvious ways).

thank you for your reply, Ron.
Does that mean by default, x is a non-zero value?