#include <stdio.h>
#include <stdlib.h>
#include <string.h>


typedef struct _node List;  /* the name if the list will be a pointer to a node, so alias List type to Node */
typedef struct _node Node;
struct _node {
  Node *next;
  char *name;
  int age;
};


/* to create a new node with a name and an age */
Node* create(char *name, int age){

  Node* anode = (Node*) malloc(sizeof(Node));

  anode->name = (char*) malloc(sizeof(char) * (strlen(name)+1));  /* need one extra space for the null character */
  strcpy(anode->name, name);
  anode->age = age;
  anode->next = NULL;
  
  return anode;   /* memory dynamically allocated in subroutines is not released after exiting the function */

}

/* to destroy an node */
void destroy(Node *anode){
  free(anode->name);
  free(anode);
}

/* to insert a node */
void insert(List* list, char* name, int age){

  Node* p = list;
  Node* anode = create(name, age);
  
  while (p->next && (strcmp(anode->name, p->next->name)>0)) p = p->next;
  anode->next = p->next;
  p->next = anode;
}

/* to search a name */
Node* search(List *list, char *name){

  Node* p = list;

  while (p->next && (strcmp(name, p->next->name)>0)) p = p->next;
  if (p->next && !strcmp(name, p->next->name)) return p->next;
  else return NULL;
}

/* to delete a node */
int delete(List *list, char* name){

  Node *q, *p = list;

  while (p->next && (strcmp(name, p->next->name)>0)) p = p->next;
  if (p->next && !strcmp(name, p->next->name)) {
    q = p->next;
    p->next = p->next->next;
    destroy(q);
    return 1;
  }
  else return 0;
}

/* to kill the whole list */
void kill(List *list){
  Node *q, *p=list;

  while (p->next){
    q = p;
    p = p->next;
    destroy(q);
  }
  destroy(p);
}

/* show a node */
void printnode(Node* anode){

  printf("%s is %d years old.\n", anode->name, anode->age);
}

/* show the whole list */
void printall(List* list){

  Node* p = list;

  while (p->next) {
    printnode(p->next);
    p = p->next;
  }
}

/* print a task selection menu */
int tasksel(){
  char ch=0;
  
  while (ch < '0' || ch > '4') {
    printf("\nPlease select a task:\n");
    printf("  1. Add a person\n");
    printf("  2. Delete a person\n");
    printf("  3. Search a person\n");
    printf("  4. Show the whole pool\n");
    printf("  0. Exit\n");
    ch = getchar();
  }

  return ch-'0';    
}

main(){

  List *pool = create("",0);  /* the header node is empty for easy programing */
  int task;
  char name[20];
  int age;
  Node *anode;

  while (task = tasksel()) {
    switch (task) {
    case 1: 
      printf("Name? ");
      scanf("%s",name); 
      printf("Age? ");
      scanf("%d",&age);
      insert(pool, name, age);
      printf("Inserted\n");
      break;
    case 2:
      printf("Name to delete? ");
      scanf("%s",name);
      if (delete(pool, name)) printf("%s is deleted.\n",name);
      else printf("%s is not on file.\n");
      break;
    case 3:
      printf("Name to search? ");
      scanf("%s", name);
      if (anode = search(pool, name)) printnode(anode);
      else printf("Not found.\n");
      break;
    case 4:
      printall(pool);
    }
  }	

  kill(pool);
}