A small but very hard to find bug

Bug is a very disgusting thing in Computer Science. In one of my subjects project, I was required to write a Hearts card game robot player. I spent several hours finished the code, but it took me 2 days to debug it. :-(. A tiny bug found in the debugging process took me a whole night, which resulted to be mistyping variable Card as C, very embarrassed!

The funniest thing was that in order to find that tiny bug, I used a screen recording software recorded the whole playing process, then simulated the whole process by re-watching the recorded video again and again, but finally came to the conclusion that there was no bug in my program! I was nearly desperate, fortunately, an accidental warning msg “singleton variable” saved my life.

Here is the video I recorded:

after playing for awhile, my robot(bottom one) stopped play.