option nolet
randomize
print "***************************************************************"
print "* programming :truebasic, random_walk (begin,end) 'version 1a'*"
print "* peter.vlasschaert@gmail.com,01/02/2020                      *"
print "***************************************************************"
x0 = 4
y0 = 0
print " begin point x coord. => ";x0
print " begin point y coord. => ";y0
x = x0
y = y0 
print "*********************"
print " end point (h,k) =>  "
print "*********************"
h = 5
k = 2
print " end point x = ";h
print " end point y = ";k
print
print "*********************"
print " domain (p,q) =>     "
print "*********************"
p = 6
q = 7
print "max: dimension  x-values = ";p
print "max: dimension  y-values = ";q
dim l(1)
nn = 0
ns = 0
nc = 0
do 

  dx = 2*x-p
  dy = 2*y-q

 done = 0
if abs(dx) = p and  abs(dy) = q then
 done = 1
nc = nc+1
x=x-sgn(dx)
y=y-sgn(dy)
print "nc = ";x,y
end if

if abs(dx) = p  then
  done = 1
ns = ns+1
x=x-sgn(dx)
end if

if abs(dy) = q  then 
  done = 1
ns = ns+1
y=y-sgn(dy)
end if
   
if done = 0 then
  done = 1
    nn = nn+1
   print " nn = "; nn
   mat redim l(nn)
l(nn) = int(4*rnd)+1
call random_walk(l(),nn,x,y)
end if
if x=h and y=k then exit do
loop
print " number of steps           :nn "; nn
print " number collision 'side  ' :ns "; ns
print " number collision 'corner' :nc "; nc
end

sub random_walk(l(),kk,x,y)
! How to use 'ELSE IF'
if 1=l(kk) then
y = y+1
else if 2=l(kk) then
y = y-1
else if 3=l(kk) then
x = x-1
ELSE                
x = x+1
END IF
end sub