I need help to make this work!! snake game

    * This how I have it but there's errors I can't find

function draw_snake(snake,food)

plot(snake(:,1),snake(:,2), 'ws',food(1,1),food(1,2), 'rs')%creates the vectors for the food and snake and plots them

whitebg([0 0 0])%creates black background axis([0, 25, 0, 25])%creates the axis for gameplay end

function checkpoint3()

global x y a b n

x =randi([10 20],1);%generates random x starting point for snake

y =randi([10 20],1);%generates random y starting point for snake

d =randi([1,4]);% generates random direction to start in for snake

a =randi([1 24],1);%generates random x coordinate for food

b =randi([1 24],1);%generates random y coordinate for food

snake=[x y];%defines the snake for x and y coordinates

food=[a b];%defines food for a and b coordinates

figure('KeyPressFcn',@my_callback);

 function my_callback(splooge,event)%callback function for movement

switch event.Character

      case 30%says if this arrow key is pressed

          d = 1;%assign this value to that arrow key

      case 31%says if this arrow key is pressed

          d = 2;%assign this value to that arrow key

      case 29 %says if this arrow key is pressed

          d = 3;%assign this value to that arrow key

      case 28 %says if this arrow key is pressed

          d = 4;%assign this value to that arrow key

end 

 end  

     while (snake(1)>=0 && snake(2)>=0 && snake(1)<=25 && snake(2)

<=25)%runs the snake as long as its within the game board

         draw_snake(snake,food)

switch d%calling callback function

   case 1%if this case is called on 

       snake(:,2)=snake(:,2)+1;%add value of 1 to y position

       draw_snake(snake,food)%draws the snake 

       pause(.1)

   case 2 

       snake(:,2)=snake(:,2)-1;%subtract value of 1 to y position

       draw_snake(snake,food)%draws the snake 

       pause(.1)

   case 3 

       snake(:,1)=snake(:,1)+1;%add value of 1 to x position

       draw_snake(snake,food)%draws the snake 

       pause(.1)

   case 4

       snake(:,1)=snake(:,1)-1;%subtracts value of 1 to x position

       draw_snake(snake,food)%draws the snake 

       pause(.1)

end

      if snake(1)==food(1) && snake(2)==food(2)%if the snake and

food are in the same position

          n=length(snake); %creates variable for length of snake 

          switch d 

              case 1%if up is called on 

                  snake(n,1)=food(1);%don't alter x position of new

segment of snake

                  snake(n,2)=food(2)-1;%have new segment follow from 
bottom 

              case 2 

                  snake(n,1)=food(1);%don't alter x position of new segment of snake 

                  snake(n,2)=food(2)+1;%have new segment follow from 
the top 
              case 3
                  snake(n,1)=food(1)-1;%have new segment follow from left 
                  snake(n,2)=food(2);%don't alter y position of new segment of snake 
              case 4 
                  snake(n,1)=food(1)+1;%have new segment follow from right 
                  snake(n,2)=food(2);%don't alter y position of new segment of snake 
          end
          food(1) = randi([1 25]);%creates a new x position for the food 
          food(2) = randi([1 25]);%creates a new y position for the food 
         % b = randi([1 25]);
      elseif snake(1)==0;%if snake exceeds boundaries display message box
         msgbox('YOU LOSE HAHAHA')
      elseif snake(2)==0;%if snake exceeds boundaries display message box
          msgbox('YOU LOSE HAHAHA')
      elseif snake(1)==25;%if snake exceeds boundaries display message box
          msgbox('YOU LOSE HAHAHA')
      elseif snake(2)==25;%if snake exceeds boundaries display message box
          msgbox('YOU LOSE HAHAHA')
      end 
     end 
end

[Jan]

Please explain the occuring problems. "there's errors" does not allow to give a meaningful advice.