Assignment Operators and Expressions (대입(할당) 연산자와 표현식)
Expressions such as
i = i + 2
in which the variable on the left hand side is repeated immediately on the right, can be written in the compressed form
i += 2
The operator += is called an assignment operator.
Most binary operators (operators like + that have a left and right operand) have a corresponding assignment operator op=, where op is one of
+ - * / % << >> &
If expr 1 and expr 2 are expressions, then
expr 1 op = expr 2
is equivalent to
expr1 = (expr1) op (expr2)
except that expr1 is computed only once. Notice the parentheses around expr2:
x *= y + 1
means
x = x * (y + 1)
rather than
x = x * y + 1
As an example, the function bitcount counts the number of 1-bits in its integer argument.
#include <stdio.h>
/* count 1 bites in x */
int bitcount(unsigned int);
int main(void)
{
unsigned int src = 14;
printf("%d \n %s", bitcount(src), "t");
return 0;
}
bitcount(unsigned int x) {
int b;
/* for (b = 0; x != 0; x >>= 1){
if (x & 01) {
b++;
}
}
*/
for (b = 0; x != 0; x &= (x-1)) {
b++;
}
return b;
} [원본에서 출력 프로그램 만들었음]
Declaring the argument x to be unsigned ensures that when it is right-shifted, vacated bits will be filled with zeros, not sign bits, regardless of the machine the program is run on.
[The C Programming Language p.50]
