plotting with changing variable values with switch case command

My whole program run with a loop . It is not showing the plot when I try below:

for nt =1:30001

...

        switch nt
        case 0
              h1=plot(x,y,x,z,'-.xr');
          case 10001
              h2=plot(x,y,x,z,'-.xg');
          case 20001
              h3=plot(x,y,x,z,'-.xk');
          case 22556
              h4=plot(x,y,x,z,'-.xb');
      end
        hold on;
        legend('1','2','3','4')

How can I plot all cases?

Answer 1

[Robert Cumming]

you need to specify the hold command before you start creating the plots.

[Meva]

I have added

   plot(h1,h2,h3,h4)

I used :

          switch nt

          case 0
                h1=plot(x,y,x,z,'-.xr');
            case 10001
                h2=plot(x,y,x,z,'-.xg');
            case 20001
                h3=plot(x,y,x,z,'-.xk');
            case 22556
                h4=plot(x,y,x,z,'-.xb');
          end

          hold on;
          plot(h1,h2,h3,h4)
          legend('1','2','3','4')

but it does not recognise h1

[Robert Cumming]

your loop starts at 1 - h1 is only activated when your loop index is 0 (doesn't look like that happens in your example)