Other
than in a for statement, when is the comma operator used?
Answer:
The
comma operator is commonly used to separate variable declarations, function
arguments, and expressions, as well as the elements of a for statement.
Look closely at the following program, which shows some of the many ways a
comma can be used:
#include
<stdio.h>
#include
<stdlib.h>
void
main(void);
void
main()
{
/* Here,
the comma operator is used to separate
three
variable declarations. */
int i, j,
k;
/* Notice
how you can use the comma operator to perform multiple initializations on the
same line. */
i = 0, j
= 1, k = 2;
printf(“i
= %d, j = %d, k = %d\n”, i, j, k);
/* Here, the comma
operator is used to execute three expressions in one line: assign k to i,
increment j, and increment k. The value that i receives is always the rightmost
expression. */
i = (j++, k++);
printf(“i = %d, j =
%d, k = %d\n”, i, j, k);
/* Here, the while
statement uses the comma operator to assign the value of i as well as test it.
*/
while (i = (rand() %
100), i != 50)
printf(“i is %d, trying
again...\n”, i);
printf(“\nGuess what?
i is 50!\n”);
}
Notice the line
that reads
i = (j++, k++);
This line
actually performs three actions at once. These are the three actions, in order:
1.
Assigns the value of k to i. This happens because the left value (lvalue)
always evaluates to the rightmost argument. In this case, it evaluates to k.
Notice that it does not evaluate to k++, because k++ is a postfix incremental
expression, and k is not incremented until the assignment of k to i is made. If
the expression had read ++k, the value of ++k would be assigned to i because it
is a prefix incremental
expression,
and it is incremented before the assignment is made.
2.
Increments j.
3.
Increments k.
Also,
notice the strange-looking while statement:
while (i
= (rand() % 100), i != 50)
printf(“i
is %d, trying again...\n”);
Here,
the comma operator separates two expressions, each of which is evaluated for
each iteration of the while statement. The first expression, to the left of the comma, assigns
i to a random number from 0 to 99.
The
second expression, which is more commonly found in a while statement,
is a conditional expression that tests to see whether i is
not equal to 50. For each iteration of the while statement,
i is assigned a new random
number,
and the value of i is checked to see that it is not 50. Eventually, i is
randomly assigned the value 50, and the while statement
terminates.
---------------------------------------------------------------------------------
Posted By Sundeep aka SunTechie
Sundeep is a Founder of Youth Talent Auzzar, a passionate blogger, a programmer, a developer, CISE and these days he is pursuing his graduation in Engineering with Computer Science dept.
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