Int stands for integer and is the type of the specified variable. Printf is the output function and Scanf is the input function. C language and database knowledge, it is best to buy two books to read, this thing can not be said in that detail. Just write Tan Haoqiang's book in C language. I don't know database for the time being, but our professional book is Introduction to Database System, edited by Susan Wang and Sashixuan, and published by Higher Education Press.