Programming Puzzles

Some companies certainly ask for these things. Specially Microsoft. Here are my favorite puzzles. Don't send me emails asking for the solutions.
1. Write a "Hello World" program in 'C' without using a semicolon.
2. Write a C++ program without using any loop (if, for, while etc) to print numbers from 1 to 100 and 100 to 1;
3. C/C++ : Exchange two numbers without using a temporary variable.
4. C/C++ : Find if the given number is a power of 2.
5. C/C++ : Multiply x by 7 without using multiplication (*) operator.
6. C/C++ : Write a function in different ways that will return f(7) = 4 and f(4) = 7
7. Remove duplicates in array
8. Finding if there is any loop inside linked list.
9. Remove duplicates in an no key access database without using an array
10. Convert (integer) number in binary without loops.
11. 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.
12. From a 'pool' of numbers (four '1's, four '2's .... four '6's), each player selects a number and adds it to the total. Once a number is used, it must be removed from the pool. The winner is the person whose number makes the total equal 31 exactly.
13. Swap two numbers without using a third variable.
14. Given an array (group) of numbers write all the possible sub groups of this group.