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Jim01Prog.txt

// * Description: Uses the Sieve of Eratosthenes method to find all primes between 2 and n. The method works by assuming all numbers are prime to start with, finding primes, then marking their multiples as not prime. Any number that has hence not been set to not prime when it is checked is therefore a prime
// 
// More info: https://www.geeksforgeeks.org/sieve-of-eratosthenes/

DECLARE limit, primeCount : INTEGER
OUTPUT "Output all primes from 2 to n. Enter a value of n"
INPUT limit

DECLARE isPrime : ARRAY[2:limit] OF BOOLEAN

// Initialise array
FOR n <-- 2 TO limit
    isPrime[n] <-- TRUE
NEXT n

FOR n <-- 2 TO limit
    IF isPrime[n] = TRUE THEN
        // Print n if it is prime
        OUTPUT n
        primeCount <-- primeCount + 1
        
        // Then mark all its multiples as not prime
        FOR multiple <-- 2 TO DIV(limit, n)
            isPrime[n * multiple] <-- FALSE
        NEXT multiple
    ENDIF
NEXT n

OUTPUT "There are " & primeCount & " primes in the range 2-" & limit

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