Task

Write a boolean function that tells whether a given integer is prime.



Remember that   1   and all non-positive numbers are not prime.

Use trial division.

Even numbers greater than   2   may be eliminated right away.

A loop from   3   to   √ n    will suffice,   but other loops are allowed.



Related tasks

   count in factors
   prime decomposition
   AKS test for primes
   factors of an integer
   Sieve of Eratosthenes
   factors of a Mersenne number
   trial factoring of a Mersenne number
   partition an integer X into N primes
   sequence of primes by Trial Division


'Reworked from the BBC Basic example
 
Public Sub Main()
Dim iNum As Integer
 
For iNum = 1 To 100
  If FNisprime(iNum) Then Print iNum & " is prime"
Next
 
End
'___________________________________________________
Public Sub FNisprime(iNum As Integer) As Boolean
Dim iLoop As Integer
Dim bReturn As Boolean = True
 
If iNum <= 1 Then bReturn = False
If iNum <= 3 Then bReturn = True
If (iNum And 1) = 0 Then bReturn = False
 
For iLoop = 3 To Sqr(iNum) Step 2
  If iNum Mod iLoop = 0 Then bReturn = False
Next
 
Return bReturn
 
End