/* File:     linked_list0b.c
 *
 * Purpose:  Implement an unsorted linked list with ops Insert (at head),
 *           Print.  This version uses a pointer to a pointer to get the
 *           updated value of head_p back to main.
 * 
 * Input:    Single character lower case letters to indicate operators, 
 *           followed by arguments needed by operators.
 * Output:   Results of operations.
 *
 * Compile:  gcc -g -Wall -o linked_list0b linked_list0b.c
 * Run:      ./linked_list0b
 *
 * Notes:
 *    1.  Repeated values are allowed in the list
 *    2.  Program assumes an int will be entered when prompted
 *        for one.
 */
#include <stdio.h>
#include <stdlib.h>

struct list_node_s {
   int    data;
   struct list_node_s* next_p;
};

void Insert(struct list_node_s** head_pp, int val);
void Print(struct list_node_s* head_p);
char Get_command(void);
int  Get_value(void);

/*-----------------------------------------------------------------*/
int main(void) {
   char command;
   int  value;
   struct list_node_s* head_p = NULL;  
      /* start with empty list */

   command = Get_command();
   while (command != 'q' && command != 'Q') {
      switch (command) {
         case 'i': 
         case 'I': 
            value = Get_value();
            Insert(&head_p, value);
            break;
         case 'p':
         case 'P':
            Print(head_p);
            break;
         case 'm': 
         case 'M':
            value = Get_value();
            printf("Member not implemented\n");
            break;
         case 'd':
         case 'D':
            value = Get_value();
            printf("Delete not implemented\n");
            break;
         case 'f':
         case 'F':
            printf("Free list not implemented\n");
            break;
         default:
            printf("There is no %c command\n", command);
            printf("Please try again\n");
      }
      command = Get_command();
   }

   // Free_list

   return 0;
}  /* main */


/*-----------------------------------------------------------------*/
void Insert(struct list_node_s** head_pp, int val) {
   struct list_node_s* temp_p;

   temp_p = malloc(sizeof(struct list_node_s));
   temp_p->data = val;
   temp_p->next_p = *head_pp;
   *head_pp = temp_p;
}  /* Insert */


/*-----------------------------------------------------------------
 * Function:   Print
 * Purpose:    print list on a single line of stdout
 * Input arg:  head_p
 */
void Print(struct list_node_s* head_p) {
   struct list_node_s* curr_p = head_p;

   printf("list = ");
   while (curr_p != NULL) {
      printf("%d ", curr_p->data);
      curr_p = curr_p->next_p;
   }  
   printf("\n");
}  /* Print */

/*-----------------------------------------------------------------
 * Function:      Get_command
 * Purpose:       Get a single character command from stdin
 * Return value:  The first non-whitespace character from stdin
 */
char Get_command(void) {
   char c;

   printf("Please enter a command (i, p, m, d, f, q):  ");
   /* Put the space before the %c so scanf will skip white space */
   scanf(" %c", &c);
   return c;
}  /* Get_command */

/*-----------------------------------------------------------------
 * Function:   Get_value
 * Purpose:    Get an int from stdin
 * Return val: The next int in stdin
 * Note:       Behavior unpredictable if an int isn't entered
 */
int  Get_value(void) {
   int val;

   printf("Please enter a value:  ");
   scanf("%d", &val);
   return val;
}  /* Get_value */