Matlab random walk problem

Consider the random walk example done in class. (Pick three non-collinear points (make a triangle). Then start at one of the points. Then we pick a number 1, 2, or 3 randomly and go halfway to that point. Repeat the process as many times as desired.)

What happens if we use a square instead of a triangle for our walk? What about a pentagon? Generate images for both a square and pentagon. Use at least 50,000 points. In class, each corner had equal chance of being chosen (1/3). Rewrite the random walk code to allow for the chance a corner is chosen to be specified. Generate the image for a square in which the bottom-left corner has a 10% chance of being chosen, the top-left has a 30% chance of being chosen, the top-right has a 25% chance of being chosen, and the bottom-right has a 35% chance of being chosen. Use at least 50,000 points.

clear
clc

x_corner=[0, 0, 1];
y_corner=[0, 1, 1];

num_steps=50000;

x=zeros(1,num_steps);
y=zeros(1,num_steps);

for i=2:num_steps
    corner_num=randi(3);
    
    x(i)=(x(i-1)+x_corner(corner_num))/2;
    y(i)=(y(i-1)+y_corner(corner_num))/2;
    
%     if corner_num == 1
%         x(i)=x(i-1)./2;
%         y(i)=y(i-1)./2;
%     elseif corner_num == 2
%         x(i)=(x(i-1)+0.5)./2;
%         y(i)=(y(i-1)+0.5)./2;
%     else
%         x(i)=(x(i-1)+1)./2;
%         y(i)=y(i-1)./2;
%     end 
end

plot(x,y,'k.')

i need some help in explaining

 x(i)=(x(i-1)+x_corner(corner_num))/2;
    y(i)=(y(i-1)+y_corner(corner_num))/2;
    
%     if corner_num == 1
%         x(i)=x(i-1)./2;
%         y(i)=y(i-1)./2;
%     elseif corner_num == 2
%         x(i)=(x(i-1)+0.5)./2;
%         y(i)=(y(i-1)+0.5)./2;
%     else
%         x(i)=(x(i-1)+1)./2;
%         y(i)=y(i-1)./2;
%     end 
end

plot(x,y,'k.')

ive been trying to wrap my head around this code but why is there a +0.5 on the first elseif and a +1 on he second one i dont get it.

also is this necessary

 x(i)=(x(i-1)+x_corner(corner_num))/2;
    y(i)=(y(i-1)+y_corner(corner_num))/2;

or should i just use the if statment and erase that.

Thank you!