A problems are simple, and I tried to submit once without testing, but I always failed to accept at once. Sometimes I get stuck in very simple mistakes. I feel that programming is so hard because of those mistakes, so I even don't have confidence to think about harder problems with advanced algorithm. Any advice please? Maybe I should change from C to another language? （But sometimes I really enjoy graspping the idea of hard problems. There are so many difficulties and exceptions for me to communicate with my computer.）