' look at a series of numbers and print out the prime numbers
' prime numbers are divisible only by unity or themselves
' this is BCX basic, a modern successor to Qbasic
 
DIM A    ' defaults to integer
 
FOR A = 1 TO 100
  IF IsPrime(A) THEN PRINT A;
NEXT
 
Pause   ' make console wait
 
FUNCTION IsPrime(Num)
  LOCAL X
  ' make exeptions for unity and 2
  IF Num = 1 THEN FUNCTION = True
  IF Num = 2 THEN FUNCTION = True
  ' leave on even numbers
  IF MOD(Num, 2) = 0 THEN EXIT FUNCTION
  FOR X = 3 TO Num - 1 STEP 2
    IF MOD(Num, X) = 0 THEN EXIT FUNCTION
  NEXT X
  FUNCTION = TRUE  ' return true if it's a Prime Number
END FUNCTION