jmp.c

 #include <setjmp.h>
 #include <stdio.h>

 int main(void) {
   jmp_buf buf;
   int a, b;

   switch(setjmp(buf)) {
   case 0:
   case 1:
       printf("Enter a number:\n");
       scanf("%d", &a);
       printf("Enter a second number:\n");
       scanf("%d", &b);
       longjmp(buf, (a == b) + 2);
   case 2:
     printf("%d != %d\n\nTry again, but enter two equal numbers this time!\n\n", a, b);
     longjmp(buf, 1);
   case 3:
     printf("%d == %d\n", a, b);
     break;
   default:
     fprintf(stderr, "???\n");
     return 1;
   }

   return 0;
 }