restaurantLinkedList created by thewizardofazz - https://repl.it/Mqxv/1

restaurantLinkedList.c

// Connor Azzarello
// COEN 11 - Lab 5
// Wednesday Lab

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

void insert();
void search();
void show();

struct node {
  char name[21];
  int size;
  struct node *next;
};

struct node * head;
struct node * tail;

int main() { //asks the user for a mode selection, converts the string to a corresponding number to be used in the switch statement
  int c = -1;
  while (c != 3) {
    char s[21];
    printf("Enter mode command: \n");
    scanf("%s", & s);
    if (!strcmp(s, "insert")) {
      c = 0;
    } else if (!strcmp(s, "search")) {
      c = 1;
    } else if (!strcmp(s, "list")) {
      c = 2;
    } else if (!strcmp(s, "quit")) {
      c = 3;
    } else {
      printf("Invalid mode, try again\n");
    }
    switch (c) {
    case 0:
      insert();
      break;
    case 1:
      search();
      break;
    case 2:
      show();
      break;
    case 3:
      printf("Thank you for using this program!");
      break;
    }
  }
  return 0;
}

void insert() { // prompts the guest for their name and table size, then either creates a head node or continues to the end of the list and adds a new tail node
  struct node * ptr = head;
  struct node * r = head; // r serves as a placeholder pointer
  char name[21];
  int size;
  int error = 0;
  printf("What is your name? \n");
  scanf("%s", name);
  while (!(ptr==NULL)) {
    if (!strcmp(ptr->name, name)) {
      printf("Duplicate name entered, try again\n");
      error = 1;
      break;
    }
    r = ptr;
    ptr = ptr->next;
  }
  ptr = r;
  if (error == 0) {
    printf("What is your group size? \n");
    scanf("%d", &size);
    if (ptr == NULL) { // when head must be created
      head = (struct node * ) malloc(sizeof(struct node));
      strcpy(head->name, name);
      head->size = size;
      tail = head;
      tail->next = NULL;
    } else { // when head already exists
      ptr = (struct node * ) malloc(sizeof(struct node));
      strcpy(ptr->name, name);
      ptr->size = size;
      r->next = ptr;
      tail = ptr;
      tail->next = NULL;
    }
  }
}

void search() { //traverses the oldest to newest list to find a reservation with a size less than or equal to the size of the table that can be seated. once it is found, it is printed and that entry is removed
  struct node * ptr = head;
  struct node * r = head;
  int size;
  printf("How big is the table that may be seated?\n");
  scanf("%d", &size);
  while (!(ptr == NULL)) {
    if(ptr->size <= size) {
      printf("%s, %d\n", ptr->name, ptr->size);
      if(!ptr == head) {
        r->next = ptr->next;
      } else {
        head = ptr->next;
        r = head;
      }
      break;
      
    }
    r = ptr;
    ptr = ptr->next;
  }
}

void show() { // traverses the list printing the name and size of every reservation left in the system
  struct node * ptr = head;
  char name[21];
  int size;
  if (ptr == NULL) {
    printf("There are no waiting list entries, try another mode\n");
  } else {
    while (!ptr == NULL) {
      printf("%s, %d\n", ptr->name, ptr->size);
      ptr = ptr -> next;
    }
  }
}