How To Call A Function Again In Case Statement In C Language?

As I under stand you want to call function from function b but not use the normal a() method to call. Correct?
Well you could call using a pointer to the function. I do not have access to a compiler here but the code would look something like this:
 
static void a(char message);
void (*ptr2a)(char) = a;
static void b(void );
void main( )
{
 for(int x = 0; x < 2; ++x)
 {
  switch(x)
  {
  case 0 : A((char)"Good Morningn");
   cycle;
   
  case 1 : B();
   cycle;
  }
 }
}
void a(char message)
{
 printf("%s",message);
}
void b(void)
{
 ptr2a((char)"and good night n");
}

If you need to call a() as the last thing in case 2, you could code your switch statement with Case 2 first, then Case 1 below it. If you then avoided calling break at the end of the Case 2 code, execution would continue on into the Case 1 code, thus calling a(). Of course, if there were any more cases below Case 1, their code would be called too unless you put a break after the a() in Case 1. Also it doesn't work if you need to do something in Case 2 after calling a(). It's incredibly bad coding style, too, but if, for some reasons, you really wanted to do that, it might be what you need.