Write a "Hello World" program in 'C' without using a semicolon.
(this is tricky)

C/C++ : Exchange two numbers without using a temporary variable.
(somehow classic way)

C/C++ : Find if the given number is a power of 2.
(somehow classic way)

Write a program whose printed output is an exact copy of the source. Needless to say, merely echoing the actual source file is not allowed.
(a bit hard to think)

source: http://developers.slashdot.org/article.pl?sid=04/12/04/0116231

1.
#include <stdio.h>
void main() {
if (printf("hello world\n")) {}
}

2.
a=a+b;
b=a-b;
a=a-b;

C/C++ : Find if the given number is a power of 2.
(somehow classic way)

can i check bit by bit?

i did not know a pair of empty brackets can follow "if"

no. 4 is tricky...

By classic (or classical?), I mean a lot of people use the method.

there are at most 32 of them...

两边应该有一边是0，如果两边都不是0，一定就不是2的power了

然后把不为0的那一边再模1<<8和除1<<8

当然这里假设是unsigned int, 32bits

just ((num - 1) & num) is enough

((num - 1) ^ num) also can

It's quite practical and quite frequent. It's important to know it, otherwise you don't understand what's going on.

#include <stdio.h>
int main (void)
{
const char *str = "#include <stdio.h>%cint main (void)%c{%c const char *str = %c%s%c;%c printf(str, 10, 10, 10, 34, str, 34, 10, 10, 10, 10);%c return 0;%c}%c";
printf(str, 10, 10, 10, 34, str, 34, 10, 10, 10, 10);
return 0;
}