go***********@gmail.com wrote:
I have a statement as follows,
a = b++;
why b=b+1 after a=b. I check the C language precedence (K&R Page 52) ,
++ should has higher precedence than = .
Rick
Let's define a new operator, @. @ has the following semantics. The
expression @x evaluates to the value x+1. The expression x@ evaluates
to the value of x. In neither case does the value of x change.
Now, let's let x = 3. What are the values of x, y and z after the
following assignments?
y = @x ;
z = x@ ;
Obviously, x = 3, y = 4 and z = 3.
The only difference between the @ operator I made up, and the ++
operator is that ++ has a side effect of incrementing the variable to
which it is applied. It still holds that ++x evalutes to the value x+1,
and x++ evalutes to the value of x.
Now, to answer your question, "a=b" doesn't happen anywhere, never, not
at all, not before "b++", and not after "b++". What happens is that,
first, the expression "b++" is evaluated. This expression evaluates to
whatever the value of b is (before incrementing). It makes no
difference that as a side effect b then gets incremented. So then, the
result of of the expression "b++" (which is b's old value) gets assigned
to a.
