' Conversion from Base 2 to Base 10
' Written by Michael L. Jones, M. S., Spring 2002
' Suffolk County Community College, Brentwood, New York

' Plan of attack:  Input a number in base 2.  Check that the number is in
' fact a binary number.  The input number will be entered as a string to
' allow for large numbers and for portability to other bases.  Start with
' the first bit, multiply by 2, add the next bit, multiply by 2 again, and so
' on until the last bit is added.  Output the result.

CLS

INPUT "What is the binary number"; bin$

PRINT

DEFLNG D  'Allows for large numbers

dec = 0   'Initalize decimal number

l = LEN(bin$)  'Get number of digits in binary number

FOR i = 1 TO l
 
  n = -1  'Sentinel value

  'Set ith digit to its decimal value

  IF MID$(bin$, i, 1) = "0" THEN n = 0
  IF MID$(bin$, i, 1) = "1" THEN n = 1

  'If the character is not a binary digit, n remains -1

  IF n = -1 THEN GOTO fail
 
  dec = 2 * dec + n  'Multiply by 2 and add new digit value

NEXT i

PRINT "The decimal equivalent of "; bin$; " is"; dec; "."

END

fail:

PRINT bin$; " is not a binary number."