Question: Bound of while loop

Hello all,

here the programme I think there are some mistakes couldnot know where please any comment will be helpful:

# Firstly, set the size limit for the grid, which shall define how many
# points there are in both the vertical and horizontal direction
size=40;
# limit is a variable used to set an unobtainable upper bound
limit=size+1;
# x defined, starting at 1, and two other variables ud (upper diagonal) and
# dd (downward diagonal) begin at 0. All three are used to iterate through
# line creation

x=1;
ud=0;
dd=0;
# Iteration through x, using the line function to create a number of
# horizontal lines up to the limit point

while(x<(limit))
line([0, size], [x, x]);
x=x+1;
end

# Now iterating through the diagonals pointing upwards, using two sets of
# lines, both starting from the line going through the origin. The first
# iterates through the lines that pass through positive x values at y=0,
# the second iterates through the lines passing through negative x values
# at y=0
# ud must be increased by 2 each time to ensure that equilateral triangles
# are formed.

while(ud<(limit))
line([(ud), (size)], [0, (size-ud)]);
line([0, (size-ud)], [(ud), (size)]);
ud=ud+2;
end

# Similar to before, except this time iterating through downward pointing
# diagonals.

while(dd<(limit))
line([(dd), 0], [0, (dd)]);
line([(size), (dd)], [(dd), (size)]);
dd=dd+2;
end

# xvector and yvector set up as two vectors holding x and y co-ordinates of
# points respectively.

xvector = zeros(1, limit);
yvector = zeros(1, limit);

# Reinitiallising x and y values for iterative purposes.

x=0;
y=0.5;
n=1;

# The program now iterates through potential y values for the potential
# points. Then it tests the value of y to see what orientation the lattice
# is at that point, then randomly selects x values to enter, iterating
# between all the possible x values in the orientation before moving on to
# the next y value.

while(y<size)
if(mod(y,1)==0.5)
x=0.5;
while(x<size)
z=rand;
if(z>0.5)
xvector(n) =x;
yvector(n) =y;
n=n+1;
end
x=x+1;
end
elseif(mod(y,2)==1)
x=0;
while(x<size)
z=rand;
if(z>0.5)
xvector(n) =x;
yvector(n) =y;
n=n+1;
end
x=x+2;
end
else
x=1;
while(x<size)
z=rand;
if(z>0.5)
xvector(n) =x;
yvector(n) =y;
n=n+1;
end
x=x+2;
end
end
y=y+0.5;

end

# The program then enters the two co-ordinate vectors saved previously into
# the scatter function.

hold;
scatter(xvector, yvector);