# Lunar Lander for the TI-95
# only integer increments of fuel?
# register 000 is position
# register 001 is velocity
# register 002 is fuel
# register 003 is acceleration
# initialize
CMS
# starting conditions
500
STO 000 # 500 ft above moon is starting position
+/-50
STO 001 # -50 ft/sec is starting velocity
60
STO 002 # 60 units fuel
# opening message
"Lunar Lander"
PAU
CLR
# prompt for fuel
LBL A
# set acceleration before each prompt
+/-5 
STO 003 # -5 ft/sec2 acceleration due to gravity
"Burn?"
BRK
# is burn more than fuel?
IF> 002
RCL 002 # burn up remaining fuel
NOP # if not, just continue
# update parameters
# assume t-step of 1 in each case
# update acceleration
ST- 002 # else remove burn from fuel
ST+ 003 # add (burn) ft/sec2 to acceleration
# update position
# x = x0 + v + a/2
RCL 000
+
RCL 001
+
RCL 003
/
2
=
STO 000
# update velocity
RCL 003 # recall acceleration
ST+ 001 # v = v0 + a
# add acceleration (*1 sec) to velocity
# did you crash
0 # 0 is greater than position?
IF> 000 
SBL D # if so print crash velocity
# if not
# report conditions
SBL B
# check if landed
0
IF= 000 # is position 0?
SBL E # if so, print closing message
0 # if not, check if fuel used up
IF= 002 # is fuel 0?
SBL C # if so, free fall
GTL A # otherwise, go back to prompt
HLT # end program
# print conditions after fuel input
LBL B
"Velocity:"
COL 16
MRG 001
PAU
CLR
"Position:"
COL 16
MRG 000
PAU 
CLR
"Fuel:"
COL 16
MRG 002
PAU
CLR
RTN
# free fall subroutine
LBL C
# calculate terminal velocity based purely from gravitational acceleration
# v = (v0^2 + 2gX)^(1/2)
(
RCL 001
x^2
+
10
*
RCL 000
)
SQR
INT
+/-
STO 001
"No fuel!"
PAU
CLR
"Free fall"
PAU
CLR
SBL D
RTN
# print crash message followed by velocity and position before crash
LBL D
"Crash!"
PAU
CLR
"Velocity:"
COL 16
MRG 001
PAU
CLR
"Position:"
COL 16
MRG 000
PAU
CLR
HLT # end program if crash
# print winning message
LBL E
"You landed!"
PAU
CLR
RTN