Thread: 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This code is absolutely horrible, outdated, unsafe, non-standard, and there's nothing concurrent about it.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.