www.spoj.pl

www.spoj.pl
A fantastic site for all budding programmers.
Has a huge collection of problems to solve and the solutions can be submitted in your choice of language. Is an online judge which tells you whether the solution you submitted was correct or not.

Every problem asks for a specific format for input and output and your program should adhere to it. It should also be run within the specified time and memory limit.
Once you have submitted your program, just go to the status option and check your program's status. If its still running then wait for a while and reload the page. once it has been compiled it will either accept it or give and error. Errors range from time limit/memory limit exceeded to compilation errors to runtime errors.

Some errors which i encountered in programs written in C:

1.Compilation error
Do not include conio.h and call getch(). When testing on your own computer you can call check but when submitting do not call them.
2.Runtime error(NZEC)
your main() should return int and at the end of main be sure to include return 0.
NZEC = non zero exit code. it comes when a program doesn't have any exit code like return 0 or exit(0).

The easiest program to start from is life,universe and everything.
So sharpen your skills. They are the only things you can count on.