the result of:
a = x, y => x
a = (i, j) => j
therefore, if we have:
x = (1 , 2)
a = (1 , 2) , 3 => 2
As said here:
The comma operator separates expressions (which have value) in a way
analogous to how the semicolon terminates statements, and sequences of
expressions are enclosed in parentheses analogously to how sequences
of statements are enclosed in braces: (a, b, c) is a sequence of
expressions, separated by commas, which evaluates to the last
expression c while {a; b; c;} is a sequence of statements, and does
not evaluate to any value. A comma can only occur between two
expressions – commas separate expressions – unlike the semicolon,
which occurs at the end of a (non-block) statement – semicolons
terminate statements.
The comma operator has the lowest precedence of any C operator, and
acts as a sequence point. In a combination of commas and semicolons,
semicolons have lower precedence than commas, as semicolons separate
statements but commas occur within statements, which accords with
their use as ordinary punctuation: a, b; c, d is grouped as (a, b);
(c, d) because these are two separate statements.
I hope this answers your question.
