21.
Determine Output:
void main()
{
      int i=1, j=2;
      switch(i)
      {
            case 1: printf("GOOD"); break;
            case j: printf("BAD"); break;
      }
}

22.
Determine Output:
void main()
{
      int i;
      printf("%d", scanf("%d", &i)); // value 10 is given as input here
}

23.
Determine Output:
void main()
{
      int i=0;
      for(;i++;printf("%d", i));
      printf("%d", i);
}

24.
Determine Output:
void main()
{
      struct xx
      {
            int x=3;
            char name[] = "hello";
      };
      struct xx *s = malloc(sizeof(struct xx));
      printf("%d", s->x);
      printf("%s", s->name); 
}

25.
Determine output:
void main()
{
      extern int i;
      i=20;
      printf("%d", sizeof(i));
}