Array of random operators is generated 3 times

[blahosyl]

Analogous to issue nr. #2 , probably has the same solution

[blahosyl]

Tutoring suggested a global variable (this commit). While this works, it's bad practice, which is why I tried to write the code without global variables in the first place.

Checked with mentor: using global variables should be OK for this project, but to be avoided for live ones.