Particles Moving Left Or Right On X-Axis

I just wrote this code to randomly place particles on the x-axis and then randomly assign a velocity so they go right or left. How could I make this code more efficient, and it doesn't seem to be working properly. Not all of the particles move during the simulation. Also, is there a better way to assign velocities to these particles, and make the code more general so I can easily input more particles? Eventually, I want the particles to be able to collide and reverse directiions every time they collide.

   % Ants On A Stick Walking Left Or Right
   
   tic
   
   clc
   clear all 
   
   axis ([0  40  0  40])
   set(gca,'box','off','ycolor','w','YTick',[])
   hold on
   
   ants = zeros(5,2);
   ants(:,1) = rand(1,5)*40;
   
   x = ants(:,1);
   y = ants(:,2);
   
   % Random velocity between -1 and 1, i.e. ants moving with random speeds,
   % more realistic
      %Vel = -1+2*rand(1,5);
   
   % Random velocity, -1 or 1 only, not zero, i.e. simplest case, ants moving left or right with
   % same speed
    Vel = randi([-1,1],6);
    numberToRemove = 0;
    Vel(Vel == numberToRemove) = [];
    Vel = Vel(1:5);
    Vel = Vel';
   
    %plot(x,y,'r.','MarkerSize',30)
   
%     for i = 1:size(ants)
%     
         for i = 0:0.5:20
             
            AssignVel = ants(:,1).*Vel(:,1);
             
             if AssignVel(1,1) < 0
                 x(1,1) = x(1,1) - 1;
             elseif AssignVel(1,1) > 0
                 x(1,1) = x(1,1) + 1;
                 
                  if AssignVel(2,1) < 0
                 x(2,1) = x(2,1) - 1;
             elseif AssignVel(2,1) > 0
                 x(2,1) = x(2,1) + 1;
                 
                 if AssignVel(3,1) < 0
                 x(3,1) = x(3,1) - 1;
             elseif AssignVel(3,1) > 0
                 x(3,1) = x(3,1) + 1;
                 
                 if AssignVel(4,1) < 0
                 x(4,1) = x(4,1) - 1;
             elseif AssignVel(4,1) > 0
                 x(4,1) = x(4,1) + 1;
                 
                 if AssignVel(5,1) < 0
                 x(5,1) = x(5,1) - 1;
             elseif AssignVel(5,1) > 0
                 x(5,1) = x(5,1) + 1;
                 
                 end
                      
                 end 
                   
                 end 
                
                 end 
             
              end
             
         plot(x,y,'r.','MarkerSize',30)
         
         pause(0.5); % change (0.1) to larger values to have a slower animation
         
         cla % Clears previous particle marker from axis
         
         end
%     
%     end
   
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