increment

[Nandadulal]

sir,
would u plz .explain me that in c language if I take a value
int p=1;
{
print("%d,%d",++p,p++);
}
the output should be 2,1 because first preincrement so , we get 2, then for p we get 1. but it shows different result why?

[weaknessforcats]

Changing the value of a variable more than once in a statement produces undefined results.

The reason is that the order of evaluation is irrelvant. In your case you have ++p and p++.

The ++p is a prefix increment. The compiler is free to increment anytime before the end of the statement. Therefore, when you get to p++ you have either 1 (the compiler is waiting) or 2 (the compiler is not waiting).

Worse, the arguments can be evaluated in any order. Maybe it goes right to left. Now its p++ first which is 2
and then ++p which is now 3.

In short, when you use a variable more than once in the same statement (called a sequence point), any rule you make up to explain the result is bogus.