Question

i = 1, 2, 3, 4, 5;

this actually assigns 1 to i.

*****I wonder if this type of assignment is actually useful somewhere?*****

Do you know some application of this syntax?

Answer 1

It’s not a “type of assignment”. The comma operator binds very loosely, looser than assignment. So you’ve written the equivalent of:

((((i = 1), 2), 3), 4), 5;

Integer literals in void contexts are useless (except maybe for avoiding warnings in macros that do nothing in certain cases, like assert), so no, there’s no use for exactly this syntax – the need for an expression which sets i to 1 and evaluates to 5 is pretty limited, and even if you found a case for that, the 2,3,4 are redundant.

More useful could be i = 1, code_that_actually_does_something;. The most frequent use of the comma operator is to sneak in multiple side-effects in a context where you’re not allowed multiple statements, such as in “if” and “while” conditions, or macros that have to evaluate as expressions.