TIMER Example; Sieve of Eratosthenes Prime Number Correction (39188)

SUMMARY

On Page 333 of the "Microsoft QuickBASIC for Apple Macintosh: BASIC Language Reference", the TIMER function Example (the Sieve of Eratosthenes benchmark program) is supposed to find prime numbers. However, it mistakenly finds some numbers that are not actually prime.

The Sieve of Eratosthenes benchmark program on Page 333 should be replaced with the version below, which correctly returns only prime numbers.

defint a-z
size=8191
dim flags(8191)
count=0
for i=2 to size
  flags(i)=-1
next
for i=2 to sqr(size)
  if flags(i) then
    for k=i*i to size step i
      flags(k)=0
    next
  end if
next

for i=0 to size
  if flags(i) then print i; : count = count + 1
next
print
print count; "primes"
while mouse(0): wend