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Ingy döt Net 2023-07-01 11:58:00 -04:00
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Task/Loops-Increment-loop-index-within-loop-body/Common-Lisp/loops-increment-loop-index-within-loop-body.lisp Normal file
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(defun primep (n) ; https://stackoverflow.com/questions/15817350/
(cond ((= 2 n) t) ; Hard-code "2 is a prime"
((= 3 n) t) ; Hard-code "3 is a prime"
((evenp n) nil) ; If we're looking at an even now, it's not a prime
(t ; If it is divisible by an odd number below its square root, it's not prime
(do* ((i 3 (incf i 2))) ; Initialize to 3 and increment by 2 on every loop
((or (> i (isqrt n)) ; Break condition index exceeds its square root
(zerop (mod n i))) ; Break condition it is divisible
(not (zerop (mod n i)))))))) ; Returns not divisible, aka prime
(do ((i 42) ; Initialize index to 42
(c 0)) ; Initialize count of primes to 0
((= c 42)) ; Break condition when there are 42 primes
(incf i) ; Increments index by unity
(if (primep i)(progn (incf c) ; If prime increment count of primes
(format t "~&~5<~d~;->~>~20<~:d~>" c i) ; Display count of primes found and the prime
(incf i (decf i))))) ; Increment index to previous index plus the prime