'                          BELTS.BAS
'      DogBasic program to calculate belt lengths/axle centres
'                    then chop to 2 decimal places

PI = 3.1415926535895#: CLS : DEFDBL A-M: N% = 0

START:  PRINT
   INPUT "First pulley diameter? - ", A
   INPUT "Second pulley diameter? - ", B
   C = (A + B) / 2
OPTIONS:
   INPUT "Calculate Axle spacing or Belt length? Enter A or B  - ", F$
   IF F$ = "A" OR F$ = "a" GOTO AXLES
   IF F$ = "B" OR F$ = "b" GOTO BELT
  GOTO OPTIONS

AXLES:
   INPUT "Enter belt length: ", D
   E = D / 2
BODGE:
   GOSUB CALCULATE
   F = G - D
   E = E - F / 2
   N% = N% + 1: PRINT N%; "Times round loop. Error ="; F
   IF E < C THEN PRINT "Too short - Try again:": GOTO AXLES
   IF ABS(F) > .000000000000001# GOTO BODGE
   PRINT "Axle centre spacing ="; : PRINT USING "#######.##"; E
  GOTO STARTAGAIN

BELT:
   INPUT "Enter axle distance: ", E
   IF E < C THEN PRINT "Too close - Try again:": GOTO BELT
   GOSUB CALCULATE
   PRINT "Length of belt ="; : PRINT USING "#######.##"; G
  GOTO STARTAGAIN

CALCULATE:
   H = A / 2 - B / 2:   REM  Where A = 1st pulley diameter, B = 2nd
   J = SQR(E ^ 2 - H ^ 2):   REM   Where E = axle distance
   M = ATN(H / J)
   K = A * PI / 2 + M * A
   L = B * PI / 2 - M * B
   G = 2 * J + K + L
  RETURN

STARTAGAIN:
   N% = 0
   PRINT
   PRINT "Again? (B from beginning, P for same pulleys or Q to quit)  ";
   INPUT "", Q$
   IF Q$ = "P" OR Q$ = "p" THEN PRINT : GOTO OPTIONS
   IF Q$ = "B" OR Q$ = "b" THEN CLS : GOTO START
   IF Q$ = "Q" OR Q$ = "q" THEN END
  GOTO STARTAGAIN



10000   REM       Subroutine to calculate belt length
10010   REM  Where A = 1st pulley diameter, B = 2nd pulley dia'
10020   REM     and E = spacing between axle centres.
10030   REM         Returns with belt length = G
10040   H = A / 2 - B / 2
10050   J = SQR(E ^ 2 - H ^ 2)
10060   M = ATN(H / J)
10070   K = A * PI / 2 + M * A
10080   L = B * PI / 2 - M * B
10090   G = 2 * J + K + L
10100   RETURN