Context Switching question

There are 2 threat to run at the same time. For example, there are number 1 and number 2, how can I run it at the same time. my coding still exit some problem, number 2 can not restore the previous number after I press ctrl^c, can anyone help me to debug it,thanks a lot:

Code:

#include <dos.h>
#include <stdio.h>
#include <stdlib.h>
#include <setjmp.h>
#include <conio.h>
jmp_buf buf_main, buf_p1, buf_p2;
void processOne();
void processTwo();
void main(void)
{
   char line[81];
   char option;
   int retVal;
   for (;;)
   {
   retVal=setjmp(buf_main);
   printf("\nEnter process number to execute the process, 'e' to exit: ");
   gets(line);
   option=line[0];
   switch(option)
   { case '1':
       if (retVal==0)
           processOne();
       else
           longjmp(buf_p1,1);
       break;

     case '2':
       if (retVal==1)
           processTwo();
       else
           longjmp(buf_p2,1);
       break;

     case 'e':
       exit(0);
       break;
   }
   }
}

void processOne()
{
   int breakRoutine();
   register clocktick=0;
   ctrlbrk(breakRoutine);
   for (;;)
   { setjmp(buf_p1);
       clrscr();
       printf("Clock of process 1 is %d", ++clocktick);
       delay(500);
   }
}

void processTwo()
{
   int breakRoutine();
   register clocktick=0;
   ctrlbrk(breakRoutine);
   for (;;)
   { setjmp(buf_p2);
       clrscr();
       printf("Clock of process 2 is %d", ++clocktick);
       delay(500);
   }
}

int breakRoutine()
{
   longjmp(buf_main,1);
   return 1;

}

This code is absolutely horrible, outdated, unsafe, non-standard, and there's nothing concurrent about it.
Oh, and it's more C than C++, so you posted on the wrong board.

If you want real multithreading, get a proper compiler, not some DOS thing (DOS does not have multithreading), then learn an appropriate threading library: pthreads on Linux, Win32 threads on Win32, or perhaps a cross-platform wrapper around them.

Originally Posted by tongboy

...how can I run it at the same time...

You can't unles you have two processors. With one processor, it is not possible to run two threads at the same. But you can make a precedence among the threads.

And...get a newer compiler!