03.linked-lists.c

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

struct listNode {
	char data;
	struct listNode *nextPtr;
};

typedef struct listNode ListNode;
typedef ListNode *ListNodePtr;

void insert(ListNodePtr *sPtr, char value);
char delete(ListNodePtr *sPtr, char value);
int isEmpty(ListNodePtr sPtr);
void printList(ListNodePtr currentPtr);
void instructions(void);

int main() {
	ListNodePtr startPtr = NULL;
	int choice;
	char item;
	
	instructions();
	printf("?");
	scanf("%d", &choice);
	
	while(choice =! 3){
		switch(choice){
			case 1:
				printf("Enter a character: ");
				scanf("\n%c", &item);
				insert(&startPtr, item);
				printlist(startPtr);
				break;
				
			case 2:
				if(!isEmpty(startPtr)){
					printf("Enter character to be deleted: ");
					scanf("\n%c", &item);
					
					if(delete(&startPtr, item)){
						printf("%c deleted!\n", item);
						printList(startPtr);
					}
					else{
						printf("%c not found.\n\n", item);
					}
				}
				else{
					printf("List is empty.\n\n");
				}
				break;
				
			default:
				printf("Invalid choice.\n\n");
				instructions();
				break;
		}
		printf("?");
		scanf("%d", &choice);
	}
	printf("End of run.\n");
	return 0;
}

void instructions(void){
	printf("Enter your choice:\n");
	printf("1 to insert an element into the list.\n");
	printf("2 to delete an element from the list.\n");
	printf("3 to end.\n");	
}

void insert(ListNodePtr *sPtr, char value){
	ListNodePtr newPtr;
	ListNodePtr previousPtr;
	ListNodePtr currentPtr;
	
	newPtr = malloc(sizeof(ListNode));
	
	if(newPtr != NULL){
		newPtr->data = value;
		newPtr->nextPtr = NULL;
		
		previousPtr = NULL;
		currentPtr = *sPtr;
		
		while(currentPtr != NULL && value > currentPtr->data){
			previousPtr = currentPtr;
			currentPtr = currentPtr->nextPtr;
		}
		
		if(previousPtr == NULL){
			newPtr->nextPtr = *sPtr;
			*sPtr = newPtr;
		}
		else{
			previousPtr->nextPtr = newPtr;
			newPtr->nextPtr = currentPtr;
		}
	}
	else{
		printf("%c not inserted. No memory available.\n", value);
	}
}

char delete(ListNodePtr *sPtr, char value){
	ListNodePtr previousPtr;
	ListNodePtr currentPtr;
	ListNodePtr tempPtr;
	
	if(value == (*sPtr)->data){
		tempPtr = *sPtr;
		*sPtr = (*sPtr)->nextPtr;
		free(tempPtr);
		return value;
	}
	else{
		previousPtr = *sPtr;
		currentPtr = (*sPtr)->nextPtr;
		
		while(currentPtr != NULL && currentPtr->data != value){
			previousPtr = currentPtr;
			currentPtr = currentPtr->nextPtr;
		}
		if(currentPtr != NULL){
			tempPtr = currentPtr;
			previousPtr->nextPtr = currentPtr->nextPtr;
			free(tempPtr);
			return value;
		}
	}
	return'\0';
}

int isEmpty(ListNodePtr sPtr){
	return sPtr == NULL;
}

void printList(ListNodePtr currentPtr){
	if(currentPtr == NULL){
		printf("List is empty.\n\n");
	}
	else{
		printf("The list is:\n");
		while(currentPtr != NULL){
			printf("%c --> ", currentPtr->data);
			currentPtr = currentPtr->nextPtr;
		}
		printf("NULL\n\n");
	}
}