Why did I make an error when introducing the basic class in the index controller when I wrote the same basic class as my teacher?

Question

Why did I write the same basic class as the teacher and made an error when introducing the basic class in the index controller?

Class 'think\controller' not found

Answer 1

This type of problem is relatively easy to solve, either the controller does not exist, or the path is wrong

Answer 2

Controller does not exist