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With commas, you can put several expressions into a place that
requires just one expression—for example, in the header of a
for
statement. This statement
for (i = 0, j = 10, k = 20; i < n; i++)
contains three assignment expressions, to initialize i
, j
and k
. The syntax of for
requires just one expression
for initialization; to include three assignments, we use commas to
bundle them into a single larger expression, i = 0, j = 10, k =
20
. This technique is also useful in the loop-advance expression,
the last of the three inside the for
parentheses.
In the for
statement and the while
statement
(see Loop Statements), a comma provides a way to perform some side
effect before the loop-exit test. For example,
while (printf ("At the test, x = %d\n", x), x != 0)