A day in exam without preparation

I'm studying mechanical engineering in my nearest college and I had completed my 2 years of study with a lot of entertainment and fun with friends.
After completing those days,I had got many unforgettable moments like birthday celebrations,exam days etc,.
But,I had got an experienced by without being prepared for exam and attended it as a time pass and I had got another idea about that exam.
In previous examinations,I had atleast an initial idea about basic concepts or I take any other bit papers for examinations and any other ideas for it.
For problematic subjects,I have those idea.But for theoretical subjects,I had a special interest on it and I will try my best for understanding concepts and writing some sentences with those concepts easily.
But,today I had got a different experienced by without any basic idea about concepts for the first time in my life
I had a chance for getting pass in this exam.But,it is not enough to increase my overall grade in my course.
So,I had planned to leave this exam and prepare well for the next semester for clearing this exam.