Simple Question for Most - Help Explain Please

[j.crater]

If you would not be assigning a value to that variable in each iteration, you would need it defined outside loop - same as you already do with secret_number variable.

Originally posted, but is incorrect, as pointed out by buran:

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Other reason is if you want to use the value after the looping has finished. Since after the loop finishes, variable is out of scope and thus rest of the code cannot access it. That is the case in your current code with number_guess commented.