学校编程类问题（Visual Studio）

I just started to learn programming, and in school the teacher used a Macbook and a program called "X-Code", and at home I have windows with Visual Studio (2017). The teaches gave 0 explanation on what "setbuf" is, and also said that we have to use scanf a little different in Visual Studio. Now I'm at home and completely helpless. Actually VS said that it would better to try scanf_s, so I did, and the program runs until I could input the "Operation". After I input the first two arguments, it stops, and the window closes itself. Can any of you help me, and give me a bit of an explanation on the things I don't understand?I just started to learn programming, and in sch