Of course it's moving past the while loop. It's just not doing anything that you see before it terminates. Try inputting a 3 digit number and see what it does.
The actual problem is here:
if (digits == 13 || digits == 15 || digits == 16) {
return digits;
}
A return statement in main will immediately terminate the program. If it has a value or variable in the statement, it will return that value to the operating system. This code is returning any cc number stored in digits that is 13, 15, or 16. If the length of the cc number is anything else, it'll run the code that follows.
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