# using  pseudocode for  procedure algorithm.
            3 quantities needed
            total loan amount dollars 
            number of months  
            interest_rate in months
            check function in TCL
     ref. number format procedure
     check_answer   new area =? desired goal , desired goal reached (yes/no)
     set answers and printout with resulting values

        # pretty print from autoindent and ased editor
        # Monthly Car Loan Payments calculator (amortized over loan)
        # written on Windows XP on eTCL
        # working under TCL version 8.5.6 and eTCL 1.0.1
        # gold on TCL WIKI, 5nov2017
        package require Tk
        package require math::numtheory
        namespace path {::tcl::mathop ::tcl::mathfunc math::numtheory }
        set tcl_precision 17
        frame .frame -relief flat -bg aquamarine4
        pack .frame -side top -fill y -anchor center
        set names {{} {total loan amount dollars :} }
        lappend names {number of months:}
        lappend names {monthly interest rate: }
        lappend names {answers: intermediate term in formula }
        lappend names {optional  :}
        lappend names {optional : }
        lappend names {total loan amount dollars: }
        lappend names {monthly payments :} 
        foreach i {1 2 3 4 5 6 7 8} {
            label .frame.label$i -text [lindex $names $i] -anchor e
            entry .frame.entry$i -width 35 -textvariable side$i
            grid .frame.label$i .frame.entry$i -sticky ew -pady 2 -padx 1 }
        proc about {} {
            set msg "Calculator for Monthly Car Loan Payments
            from TCL WIKI,
            written on eTCL "
            tk_messageBox -title "About" -message $msg } 
       proc ::tcl::mathfunc::precision {precision float}  {
            #  tcl:wiki:Floating-point formatting, [AM]
            set x [ format "%#.5g" $float ]
            return $x
           }   
            #proc errorx always returns a positive error. 
            #Normally assume $aa is human estimate,
            #assume $bb is divinely exact.
       proc errorx  {aa bb} {expr { $aa > $bb ?   (($aa*1.)/$bb -1.)*100. : (($bb*1.)/$aa -1.)*100.}}
       proc calculate {     } {
            global answer2
            global side1 side2 side3 side4 side5
            global side6 side7 side8 
            global testcase_number
            incr testcase_number 
            set side1 [* $side1 1. ]
            set side2 [* $side2 1. ]
            set side3 [* $side3 1. ]
            set side4 [* $side4 1. ]
            set side5 [* $side5 1. ]
            set side6 [* $side6 1. ]
            set side7 [* $side7 1. ]
            set side8 [* $side8 1. ]
            set loan_amount $side1
            set number_months $side2
            set monthly_interest_rate $side3
            set term1 [+ 1. $monthly_interest_rate ]
            set monthly_payments [/  [* $loan_amount $monthly_interest_rate ] [- 1. [** $term1 [* -1.  $number_months ]]]]
            set side4 $monthly_payments
            set side7 $loan_amount
            set side8 [::tcl::mathfunc::precision 4 $monthly_payments ]
                    }
        proc fillup {aa bb cc dd ee ff gg hh} {
            .frame.entry1 insert 0 "$aa"
            .frame.entry2 insert 0 "$bb"
            .frame.entry3 insert 0 "$cc"
            .frame.entry4 insert 0 "$dd"
            .frame.entry5 insert 0 "$ee"
            .frame.entry6 insert 0 "$ff" 
            .frame.entry7 insert 0 "$gg"
            .frame.entry8 insert 0 "$hh" 
             }
        proc clearx {} {
            foreach i {1 2 3 4 5 6 7 8 } {
                .frame.entry$i delete 0 end } }
        proc reportx {} {
            global answer2
            global side1 side2 side3 side4 side5
            global side6 side7 side8
            global testcase_number
            console show;
            puts "%|table $testcase_number|printed in| tcl wiki format|% "
            puts "&| quantity| value| comment, if any|& "
            puts "&| $testcase_number:|testcase_number | |&"
            puts "&| $side1 :|total loan amount dollars |   |&"
            puts "&| $side2 :|number of months | |& "  
            puts "&| $side3 :|function factor | |& "
            puts "&| $side4 :|answers: intermediate term in formula| |&"
            puts "&| $side5 :|optional  | |&"
            puts "&| $side6 :|optional |  |&"
            puts "&| $side7 :|total loan |  |&"
            puts "&| $side8 :|monthly interest rate |  |&" 
            }
        frame .buttons -bg aquamarine4
        ::ttk::button .calculator -text "Solve" -command { set side8 0 ; calculate   }
        ::ttk::button .test2 -text "Testcase1" -command {clearx;fillup 2600.  24.0  0.1 289.0  0.0   0.0    2600.00  289.38}
        ::ttk::button .test3 -text "Testcase2" -command {clearx;fillup 1000.0 24.0 0.2 202.0   0.0   0.0  1000.00     202.55}
        ::ttk::button .test4 -text "Testcase3" -command {clearx;fillup 10000.0 24.0 0.2  2025.0  0.0    0.0  10000.00  2025.50}
        ::ttk::button .clearallx -text clear -command {clearx }
        ::ttk::button .about -text about -command {about}
        ::ttk::button .cons -text report -command { reportx }
        ::ttk::button .exit -text exit -command {exit}
        pack .calculator  -in .buttons -side top -padx 10 -pady 5
        pack  .clearallx .cons .about .exit .test4 .test3 .test2   -side bottom -in .buttons
        grid .frame .buttons -sticky ns -pady {0 10}
               . configure -background aquamarine4 -highlightcolor brown -relief raised -border 30
        wm title . "Monthly Car Loan Payments Calculator"     
     

  puts " %| testcase $testcase_number | value| units |comment |%"
  puts " &| volume| $volume| cubic meters |based on length $side1 and width $side2   |&"