As a Programmer I am agree with your teacher. yes it is good if you can write a program on computer. But that's not the case in every scenario. Suppose your are building a complex software at that time you have to foresee the potential breaking points before you start writing your code so you can avoid the bugs at that time code or logic on paper will help you.
I personally prefer single quotes.
There are some advantages of double quotes like you don't have to close quotes every time you use variable. But I prefer singles because its cleaner and it helps me read my own code better.
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