|Few things on "how"
Have a pseudoce about WHAT is the purpose of the code showing inputs / outputs.
Than CHANGING the output would be more visible in code.
Get into habit to comment your code. I do 80% comments and 20% real code ratio.
I realize your construct your code using your native language that write it in English, so that is why there are no (English) comments in your code.
Find a IDE which allows you to set breakpoints or use some other method to track your code.