The Comma Operator
The comma is frequently used in C as a simple punctuation mark, to separate variable declarations, function arguments, etc. In certain situations, the comma acts as an operator.
You can form an expression by separating two sub expressions with a comma. The result is as follows:
Both expressions are evaluated, with the left expression being evaluated first.
- The entire expression evaluates to the value of the right expression.
For example, the following statement assigns the value of b to x, then increments a, and then increments b:
x = (a++, b++);
C operator precedence (Summary of C operators)
Rank and Associativity |
Operators |
1(left to right) |
() [] -> . |
2(right to left) |
! ~ ++ -- * (indirection) & (address-of) (type)
sizeof + (unary) - (unary) |
3(left to right) |
* (multiplication) / % |
4(left to right) |
+ - |
5(left to right) |
<< >> |
6(left to right) |
< <= > >= |
7(left to right) |
= = != |
8(left to right) |
& (bitwise AND) |
9(left to right) |
^ |
10(left to right) |
| |
11(left to right) |
&& |
12(left to right) |
|| |
13(right to left) |
?: |
14(right to left) |
= += -= *= /= %= &= ^= |= <<= >>= |
15(left to right) |
, |
() is the function operator; [] is the array operator. |
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Let us take an example of use of operators:
/* Use Of Operators */
int main()
{
int x = 0, y = 2, z = 1025;
float a = 0.0, b = 3.14159, c = -37.234;
/* incrementing */
x = x + 1; /* This increments x */
x++; /* This increments x */
++x; /* This increments x */
z = y++; /* z = 2, y = 3 */
z = ++y; /* z = 4, y = 4 */
/* decrementing */
y = y - 1; /* This decrements y */
y--; /* This decrements y */
--y; /* This decrements y */
y = 3;
z = y--; /* z = 3, y = 2 */
z = --y; /* z = 1, y = 1 */
/* arithmetic op */
a = a + 12; /* This adds 12 to a */
a += 12; /* This adds 12 more to a */
a *= 3.2; /* This multiplies a by 3.2 */
a -= b; /* This subtracts b from a */
a /= 10.0; /* This divides a by 10.0 */
/* conditional expression */
a = (b >= 3.0 ? 2.0 : 10.5 ); /* This expression */
if (b >= 3.0) /* And this expression */
a = 2.0; /* are identical, both */
else /* will cause the same */
a = 10.5; /* result. */
c = (a > b ? a : b); /* c will have the max of a or b */
c = (a > b ? b : a); /* c will have the min of a or b */
printf("x=%d, y=%d, z= %d\n", x, y, z);
printf("a=%f, b=%f, c= %f", a, b, c);
return 0;
}
and the result of this program will be displayed on the screen as:
x=3, y=1, z=1
a=2.000000, b=3.141590, c=2.000000 |
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