#LoanCalc.bas
#   for HotPaw Basic 1.4.5  8/2005
#   example version 4.0
#
#  example equation to solve :
#  loan amortisazion example
#
e$="paymnt = fn pmt(price-down, rate/1200, 12*years)"
#
#  provide realistic  initial values :
price = 250000
down = 50000
rate = 10
years = 30
# 
# solver program setup
#
dim vn$(10), vv(10), vf(10)
draw -1
# show equation
form fld 6,20,130,24,e$,1
  vf(0) = fn formindex()
top:
form btn 140,20, 18,12,"OK",1
a$ = input$(1)
# get equation
e1$=s$(0) : e$=e1$
e2$=e$
form fld 0,vf(0),0,0,e2$,1
# get list of variables in equation
v$=fn getvarlist(e1$)
c$=","
for ii=1 to 9
  vn$(ii)=field$(v$,ii,c$)
  if vn$(ii)="" then exit for : else nn=ii
next ii
#
# create solver form
#
q$="solve"
for ii=1 to nn
  vv(ii)=eval(vn$(ii))
  y=32+16*ii
  form fld 52,y,58,12, (str$(vv(ii))+"  "),1
  vf(ii) = fn formindex()
  form btn 120,y,32,12,q$,1
  fn setformkey(fn formindex(), 48+ii)
next ii
form btn 0,160,0,0,"Done",1
# draw variable names
for ii=1 to nn
  y=32+16*ii
  draw vn$(ii), 16,y
next ii
#
# wait for input
#
while 1
  a$ = input$(1)
  if asc(a$)=3 then end
  if asc(a$)<32
    form reset 0,0,0,0,t$,-1 :' clear it
    form fld 6,20,130,24,s$(0),1
    goto top:
  endif
# get button number
tt = val(a$)
for i=1 to nn
  vv(i)=val(s$(i))
  fn assign2var(vn$(i), vv(i))
  f$=str$(vv(i))+"    "
  form fld 0,vf(i),0,0,f$,1
next i
# clear unknown
form fld 0,vf(tt),0,0,"  ",1
# attempt to solve
  x3=fn solve1(e2$,vn$(tt),vv(tt))
  x3=fn solve1(e2$,vn$(tt),x3)
  vv(tt)=x3
  fn assign2var(vn$(tt), x3)
# display results
d$="+#.##"
for i=1 to nn
  f$=fn format$(vv(i),d$)
  if i>3 then f$=str$(vv(i))
  form fld 0,vf(i),0,0,f$,1
next i
# check for amount of error
# max error allowed
ermax = 0.001
# check solution
i=instr(e$,"=")
if i>0
  er$=mid$(e$,1,i-1)+" - "
  er$=er$+mid$(e$, i+1)
else
  er$=e$
endif
# warn if solution didn't converge
if ermax > 0
  er = eval(er$)
  if (abs(er) > ermax)
    err$="ERROR = " + fn format$( er, "#.#E##")
    err$=err$+"                        "
    draw err$, 50, 147, 1
    erflag=1
  else
    err$="                        "
    draw err$, 50, 147, 1
    draw err$, 95, 147, 1
  endif
endif
# go back to input loop
wend
end
#
# Copyright 2004 rhn @ HotPaw
#