Decimal to Binary (qbasic/BCX)

' converting a decimal integer to a binary string
' BCX basic
'

'
' postfix $ indicates a string variable
' could be written as:  dim A as String
'
dim A$


A$ = dec2bin$(123)
print "decimal 123 = binary ", A$

A$ = dec2bin$(255)
print "decimal 255 = binary ", A$

pause  ' wait


'
' postfix $ in function name indicates that the function returns a string
' could be written as:  function dec2bin Optional (a, digits=0) as String
' keyword Optional indicates parameter digits is optional and defaults to 0
' variables declared within the function are local
'
Function dec2bin$ Optional (a, digits=0)
  dim k, tmp, t  ' default to integer variables
  dim T$         ' string variable

  ' don't know the number of digits in a, so figure it out
  if digits = 0 then   
    tmp = a
    while tmp > 0
      tmp = tmp >> 1   ' shift right by 1 place
      digits++         ' increment by 1, same as: digits = digits + 1
    wend
  end if
  
  t = 1
  
  ' do the conversion to zeros and ones
  for k = 1 to digits
    tmp = a AND t
    if tmp = 0 then
      T$ = "0" & T$
    else
      T$ = "1" & T$
    end if
    t = t << 1    ' shift left by 1 place
  next

  function = T$   ' result is in T$, return this
End Function