Binary Search Tree

This is a discussion on Binary Search Tree within the C Programming forums, part of the General Programming Boards category; Hello, I am currently working on a binary search tree that acts as a phone book. I am nearly completed ...

  1. #1
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    Binary Search Tree

    Hello, I am currently working on a binary search tree that acts as a phone book. I am nearly completed with it and all functions seem to work properly except in two cases:

    An error message will not print to the screen when trying to delete, edit, or search for a node that does not exist.

    And if a node has a left and right branch, it can't be deleted.

    I've been trying to fix these problems, and I was hoping that you fine folk could assist me. If you feel uncomfortable with direct answers, just giving a nudge in the right direction would be great.

    Here is my code.

    Code:
    #include <stdio.h>
    #include <string.h>
    #include <stdlib.h>
    
    /*Create phone book entry structure.*/
    typedef struct pbentry {
    	char lastname[16];
    	char firstname[11];
    	char phone[11];
    	char email[26];
    } Entry;
    
    /*Create tree node structure.*/
    struct tree_node {
    	Entry data;
    	struct tree_node *left;
    	struct tree_node *right;
    };
    
    /*Necessary functions.*/
    struct tree_node * insert(struct tree_node *p, Entry e);
    struct tree_node * create_node (struct tree_node *q, struct tree_node *r, Entry e);
    struct tree_node * delete_node (struct tree_node *p, char l[], char f[]);
    struct tree_node * findmin(struct tree_node *p);
    struct tree_node * edit_node (struct tree_node *p, char l[], char f[]);
    void search_node(struct tree_node *p, char l[], char f[]);
    void print_tree(struct tree_node *p);
    
    int main(void)
    {
    	int option = 0; /*Variable for option selection.*/
    	Entry e;  /*Basic phone book entry*/
    	struct tree_node *p = NULL; /*Basic tree node*/
    	char ln[16]; /*Used for deletions, editing, and searching*/
    	char fn[11]; /*Used for deletions, editing, and searching*/
    
    	/*Return to menu after each instruction until the user quits.*/
    	while (option != 6) {
    		/*Show user the option menu.*/
    		printf("MENU\n");
    		printf("1. Add\n");
    		printf("2. Delete\n");
    		printf("3. Edit\n");
    		printf("4. Search\n");
    		printf("5. List\n");
    		printf("6. Quit\n");
    		/*Get option from the user.*/
    		printf("\nPlease select an option: ");
    		scanf("%d", &option);
    		/*If option is 1 (Add):*/
    		if (option == 1) {
    			/*Take in subject data from the user.*/
    			printf("Please enter the last name: ");
    			scanf("%s", &e.lastname);
    			printf("Please enter the first name: ");
    			scanf("%s", &e.firstname);
    			printf("Please enter the phone number: ");
    			scanf("%s", &e.phone);
    			printf("Please enter the e-mail address: ");
    			scanf("%s", &e.email);
    			/*Create a new node.*/
    			p = insert(p, e);
    			/*Confirm node creation.*/
    			printf("Record added successfully.\n\n");
    		}
    		/*If option is 2 (Delete):*/		
    		else if (option == 2) {
    			/*Take in subject data from the user.*/
    			printf("Please enter the last name: ");
    			scanf("%s", &ln);
    			printf("Please enter the first name: ");
    			scanf("%s", &fn);
    			/*Delete a node.*/
    			p = delete_node(p, ln, fn);
    		}
    		/*If option is 3 (Edit):*/		
    		else if (option == 3) {
    			/*Take in subject data from the user.*/
    			printf("Please enter the last name: ");
    			scanf("%s", &ln);
    			printf("Please enter the first name: ");
    			scanf("%s", &fn);
    			/*Edit a node.*/
    			p = edit_node(p, ln, fn);
    		}
    		/*If option is 4 (Search):*/		
    		else if (option == 4) {
    			/*Take in subject data from the user.*/
    			printf("Please enter the last name: ");
    			scanf("%s", &ln);
    			printf("Please enter the first name: ");
    			scanf("%s", &fn);
    			/*Search for a node.*/
    			search_node(p, ln, fn);
    		}
    		/*If option is 5 (List):*/		
    		else if (option == 5) {
    			print_tree(p);
    		}
    		/*If option is 6 (Quit):*/		
    		else if (option == 6) {
    			/*End the program.*/
    			break;
    		}
    		/*If the user does not select an existing option.*/		
    		else {
    			/*Print error message.*/
    			printf("That option does not exist. Please try again.\n\n");
    		}
    
    	}
    	return 0;
    }
    
    /*Adds a node to the tree.*/
    struct tree_node * insert(struct tree_node *p, Entry e) {
    	/*If there is no root:*/
    	if (p == NULL) {
    		/*Create a root.*/
    		p = create_node(NULL, NULL, e);
    	}
    	/*If there is a root, and the entry belongs before the root:*/
    	else if (strcmp(e.lastname, p->data.lastname) < 0) {
    		/*Add before root.*/
    		p->left = insert(p->left, e);
    	}
    	/*If there is a root, and the entry belongs after the root:*/
    	else if (strcmp(e.lastname, p->data.lastname) > 0) {
    		/*Add after root.*/
    		p->right = insert(p->right, e);
    	}
    	/*If there is a root, and the lastnames are identical: */
    	else {
    		/*If entry belongs before root: */
    		if (strcmp(e.firstname, p->data.firstname) < 0) {
    			/*Add before root.*/
    			p->left = insert(p->left, e);
    		}
    		/*If entry belongs after root: */
    		else if (strcmp(e.firstname, p->data.firstname) > 0) {
    			/*Add after root.*/
    			p->right = insert(p->right, e);
    		}
    		/*If entries are the same: */
    		else {
    			/*Do nothing.*/
    			return p;
    		}
    	}
    	/*Return revised tree.*/
    	return p;
    }
    
    /*Creates a new node.*/
    struct tree_node * create_node (struct tree_node *q, struct tree_node *r, Entry e) {
    	struct tree_node* newnode;
    	newnode = (struct tree_node*)(malloc(sizeof(struct tree_node)));
    	newnode->data = e;
    	newnode->left = q;
    	newnode->right = r;
    	return newnode;
    }
    
    /*Deletes a node from the tree.*/
    struct tree_node * delete_node (struct tree_node *p, char l[], char f[]) {
    	/*If entry is before root:*/
    	if (strcmp(l, p->data.lastname) < 0 || strcmp(f, p->data.firstname) != 0) {
    		/*Delete from before root.*/
    		p->left = delete_node(p->left, l, f);
    	}
    	/*If entry is after root:*/
    	else if (strcmp(l, p->data.lastname) > 0 || strcmp(f, p->data.firstname) != 0) {
    		/*Delete from after root.*/
    		p->right = delete_node(p->right, l, f);
    	}
    	/*If entry is located and has a left and right branch:*/
    	else if (p->left != NULL && p->right != NULL) {
    		/*Find which branch moves up in the tree.*/
    		p->data = findmin(p->right)->data;
    		p->right = delete_node(p->right, l, f);
    		/*Confirm node deletion.*/
    		printf("Record deleted successfully.\n\n");
    	}
    	/*If entry is located and has a left branch:*/
    	else if (p->left != NULL) {
    		/*Move left branch up.*/
    		p = p->left;
    		/*Confirm node deletion.*/
    		printf("Record deleted successfully.\n\n");
    	}
    	/*If entry is located and has a right branch:*/
    	else if (p->right != NULL) {
    		/*Move right branch up.*/
    		p = p->right;
    		/*Confirm node deletion.*/
    		printf("Record deleted successfully.\n\n");
    	}
    	/*If entry is not found:*/
    	else {
    		/*Error.*/
    		printf("Record could not be found.\n\n");
    	}
    	/*Return revised tree.*/
    	return p;
    }
    
    /*Finds the leftmost node in the right branch.*/
    struct tree_node * findmin(struct tree_node *p) {
    	/*If left node is not empty.*/
    	if (p->left != NULL) {
    		/*Go to the left node.*/
    		findmin(p->left);
    	}
    	/*Return leftmost node.*/
    	return p;
    }
    
    /*Edits a node's data.*/
    struct tree_node * edit_node (struct tree_node *p, char l[], char f[]) {
    	char num[11]; /*Used to determine course of action.*/
    	char e[26]; /*Used to determine course of action.*/
    	/*If entry is before root:*/
    	if (strcmp(l, p->data.lastname) < 0) {
    		/*Check before root.*/
    		edit_node(p->left, l, f);
    	}
    	/*If entry is after root:*/
    	else if (strcmp(l, p->data.lastname) > 0) {
    		/*Check after root.*/
    		edit_node(p->right, l, f);
    	}
    	/*If last name is found and first names are different:*/
    	else if (strcmp(l, p->data.lastname) == 0 && strcmp(f, p->data.firstname) != 0) {
    		/*If entry is before root.*/
    		if (strcmp(f, p->data.firstname) < 0) {
    			/*Check before root.*/
    			edit_node(p->left, l, f);
    		}
    		/*If entry is after root.*/
    		if (strcmp(f, p->data.firstname) > 0) {
    			/*Check after root.*/
    			edit_node(p->right, l, f);
    		}
    	}
    	/*If entry is located:*/
    	else if (strcmp(l, p->data.lastname) == 0 && strcmp(f, p->data.firstname) == 0) {
    		/*Ask for new phone number and retreive.*/
    		printf("New phone number (Enter s to skip): ");
    		scanf("%s", &num);
    		/*If skipped:*/
    		if (strcmp(num, "s") == 0) {
    			/*Ask for new email address and retreive.*/
    			printf("New email address (Enter s to skip): ");
    			scanf("%s", &e);
    			/*If skipped:*/
    			if (strcmp(e, "s") == 0) {
    				/*Confirm node edit.*/
    				printf("Record edited successfully.\n\n");
    				/*Return revised tree.*/
    				return p;
    			}
    			/*If email address is to be changed:*/
    			else {
    				/*Change email*/
    				strcpy(p->data.email, e);
    				/*Confirm node edit.*/
    				printf("Record edited successfully.\n\n");
    			}
    		}
    		/*If phone number is to be changed:*/
    		else {
    			/*Change phone number.*/
    			strcpy(p->data.phone, num);
    			/*Ask for new email address and retreive.*/
    			printf("New email address (Enter s to skip): ");
    			scanf("%s", &e);
    			/*If skipped:*/
    			if (strcmp(e, "s") == 0) {
    				/*Confirm node edit.*/
    				printf("Record edited successfully.\n\n");
    				/*Return revised tree.*/
    				return p;
    			}
    			/*If email address is to be changed:*/
    			else {
    				/*Change email.*/
    				strcpy(p->data.email, e);
    				/*Confirm node edit.*/
    				printf("Record edited successfully.\n\n");
    			}
    		}
    	}
    	/*If entry is not found:*/
    	else {
    		/*Error.*/
    		printf("Record could not be found.\n\n");
    	}
    	/*Return revised tree.*/
    	return p;
    }
    
    /*Searches for a node and retrieves data.*/
    void search_node(struct tree_node *p, char l[], char f[]) {
    	/*If entry is before root:*/
    	if (strcmp(l, p->data.lastname) < 0) {
    		/*Check before root.*/
    		search_node(p->left, l, f);
    	}
    	/*If entry is after root:*/
    	else if (strcmp(l, p->data.lastname) > 0) {
    		/*Check after root.*/
    		search_node(p->right, l, f);
    	}
    	/*If last name is found and first names are different:*/
    	else if (strcmp(l, p->data.lastname) == 0 && strcmp(f, p->data.firstname) != 0) {
    		/*If entry is before root.*/
    		if (strcmp(f, p->data.firstname) < 0) {
    			/*Check before root.*/
    			search_node(p->left, l, f);
    		}
    		/*If entry is after root.*/
    		if (strcmp(f, p->data.firstname) > 0) {
    			/*Check after root.*/
    			search_node(p->right, l, f);
    		}
    	}
    	/*If entry is located:*/
    	else if (strcmp(l, p->data.lastname) == 0 && strcmp(f, p->data.firstname) == 0) {
    		/*Print out data.*/
    		printf("%s, %s, %s, %s\n\n", p->data.lastname, p->data.firstname, p->data.phone, p->data.email);	
    	}
    	/*If entry is not found:*/
    	else {
    		/*Error.*/
    		printf("Record could not be found.\n\n");
    	}
    }
    
    /*Prints contents of tree.*/
    void print_tree(struct tree_node *p)
    {
    	/*If tree has nodes:*/
    	if (p != NULL) {
    		/*Print node data.*/
    		print_tree(p->left);
    		printf("%s, %s, %s, %s\n\n", p->data.lastname, p->data.firstname, p->data.phone, p->data.email);
    		print_tree(p->right);
    	}
    }

  2. #2
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    Well, I just solved my second problem. Turns out I never supplied a case for if a node didn't have a left or right branch, which is why it didn't work when I tried to delete all the nodes. I was mistaken about what the error-causing factor was.

    However, I still can't get an error message to pop up if I try to delete, edit, or search for a node that doesn't exist, and I'm sure it must be because I need to supply some kind of specific case for such an event instead of just using else, but I can't think of what that might be.

  3. #3
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    Code:
        if (p == NULL) {
            return NULL;
        }
    putting this at the beginning of each affected function should fix it.

    On the search function just return; rather than return NULL;
    Also you can add a message like

    Code:
        if (p == NULL) {
            printf("Member not found.\n");
            return;
        }

  4. #4
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    Now see, my problem was that I didn't think to put all that at the beginning instead of the end. That makes a lot more sense. Brian, you're a lifesaver. Thank you so much for your assistance.

  5. #5
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    No problem. I've been doing a lot of structures this week, and if you ever get an error that brings up a box you know it's because you didn't check if something equals null.

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