Another Puzzle

[Sameer Jamal]

Suppose x and y are distinct identifiers of type integer. show a simple
context into which either of the code fragments x = 0; y = 1 or y = 1; x= 0 can be substituted so that in most programming languages the resulting substitutions yield different results.
[ February 22, 2006: Message edited by: Sameer Jamal ]

[Manish Hatwalne]

int x=0;
int y=1;

System.out.println(x-y);
System.out.println(x/y);

- Manish

[Vishnu Prakash]

x++, y--

[Jim Yingst]

Sameer, is the ':' intentional in "x:= 0"? If so, is it intentional that all 3 other expressions do not include a ':'?

I'm thinking maybe the solution is in a for loop, where

int x, y;
for (x = 0; y == 1; )

is different in effect from

int x, y;
for (y = 1; x == 0; )

However we need to distinguish between = and == to get this to compile. Most other languages nowadays distinguish between relational operators and assignments - seeing := makes me think of Pascal for example. I don't see a good way to make your text work for any language I'm currently familiar with. Can you confirm the exact syntax, and maybe give a specific languuage it definitely works in?

[Sameer Jamal]

Originally posted by Jim Yingst:
Sameer, is the ':' intentional in "x:= 0"? If so, is it intentional that all 3 other expressions do not include a ':'?

No it was not intentional it was just a typing mistake.
There are few languages where comparison operator '==' will not work for eg: VB 6.0

The context can be

        Procedure P(x, y);{
         x, y : integer-var;
         . . . ;
        };
        do {P(z, z)}

In the case that the first code fragment is substituted for the ellipsis, the effect is to set z to 1, while in the second case z gets set to 0.
[ February 22, 2006: Message edited by: Sameer Jamal ]