Because minutes is being used as the control var for the do/while loop, it must be declared before the do loop. It's also good form to initialize it at that time too. Also, be sure that you aren't redeclaring it inside the loop (with the keyword int), which would create a second shadow variable with the same name.
int minutes = -1;
minutes = ...;
} while minutes < 0;
When a var is declared inside a set of curly braces, it only exists inside that immediate pair of curly braces. It ceases to exist outside of the immediately closest braces surrounding it. This is called variable scope and will be discussed in a later lecture.
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