#include <stdio.h>

#define MAXLEN 100

typedef struct {
   char element[MAXLEN];
   int top;
} stack;

stack init ()
{
   stack S;

   S.top = -1;
   return S;
}

int isEmpty ( stack S )
{
   return (S.top == -1);
}

int isFull ( stack S )
{
   return (S.top == MAXLEN - 1);
}

char top ( stack S )
{
   if (isEmpty(S)) {
      fprintf(stderr, "top: Empty stack\n");
      return '\0';
   }
   return S.element[S.top];
}

stack push ( stack S , char ch )
{
   if (isFull(S)) {
      fprintf(stderr, "push: Full stack\n");
      return S;
   }
   ++S.top;
   S.element[S.top] = ch;
   return S;
}

stack pop ( stack S )
{
   if (isEmpty(S)) {
      fprintf(stderr, "pop: Empty stack\n");
      return S;
   }
   --S.top;
   return S;
}

void print ( stack S )
{
   int i;

   for (i = S.top; i >= 0; --i) printf("%c",S.element[i]);
}

int main ()
{
   stack S;

   S = init(); printf("Current stack : "); print(S); printf(" with top = %c.\n", top(S));
   S = push(S,'d'); printf("Current stack : "); print(S); printf(" with top = %c.\n", top(S));
   S = push(S,'f'); printf("Current stack : "); print(S); printf(" with top = %c.\n", top(S));
   S = push(S,'a'); printf("Current stack : "); print(S); printf(" with top = %c.\n", top(S));
   S = pop(S); printf("Current stack : "); print(S); printf(" with top = %c.\n", top(S));
   S = push(S,'x'); printf("Current stack : "); print(S); printf(" with top = %c.\n", top(S));
   S = pop(S); printf("Current stack : "); print(S); printf(" with top = %c.\n", top(S));
   S = pop(S); printf("Current stack : "); print(S); printf(" with top = %c.\n", top(S));
   S = pop(S); printf("Current stack : "); print(S); printf(" with top = %c.\n", top(S));
   S = pop(S); printf("Current stack : "); print(S); printf(" with top = %c.\n", top(S));
}