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:

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#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;

}

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This code is absolutely horrible, outdated, unsafe, non-standard, and there's nothing concurrent about it.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

Quote:

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Originally Posted by tongboy

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

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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!