Predecrement and Post-decrement,,need help!!!!!!

Question

Hi everyone,
I tried to compile the following code on my pc, and it produced different results as I expected, can anyone explain to me why? thanks
public static void main (String[] args)
   int a=5,b=5,c=5,d=5;
   System.out.println( a-- + a); //line one
   System.out.println( b + b--); //line two
   System.out.println( --c + c);  //line three
   System.out.println(d + --d);  //line four
}where I think line one should produce the output 10, but I got the result 9 instead. Is it that "a--" was supposed to be evaluated after the "a+a"????
Line two produces 10, and I am satisfied with the result, because b-- was evaluated after "b+b" .
At line three, it's getting more confused, --c+c produces 8 !!!!!* , can anyone tell me why??????
Line four produces 9, why???
I also have a few more questions regarding this issue:
*if  d=4
how would expression
d-- + --d   //exp 1
--d + d--   //exp 2
d-- + d--   //exp 3
--d + --d    //exp 4be evaluated????????*
plz anybody can explain this to me, thanks!!!!
Edited by: df2334 on Jan 2, 2008 4:11 PM
Edited by: df2334 on Jan 2, 2008 4:18 PM

Answer 1

df2334 wrote:
Hi everyone,
I tried to compile the following code on my pc, and it produced different results as I expected, can anyone explain to me why? thanks
public static void main (String[] args)
int a=5,b=5,c=5,d=5;
System.out.println( a-- + a); //line one
System.out.println( b + b--); //line two
System.out.println( --c + c);  //line three
System.out.println(d + --d);  //line four
// 1
a is 5, so the value of the expression "a--" is 5 a is then decremented to 4. So it's 5 + 4.
// 2
b is 5. The value of the expression "b--" is 5. So it's 5 + 5. b is then decremented to 4.
// 3
c is 5. c is decremented to 4 and the value of expression "--c" is 4. So it's 4 + 4.
// 4
d is 5. d is then decremented to 4. The value of expression "--d" is 4. So it's 5 + 4.
And the lesson we learn is: Don't use the variable you're ++ing or ing in the same statement you're ++/ing it in other than the ++/-- expression.