I had completed my code for my project, then decided to change it. I now have an error that I do not understand. C4715 which according to MSDN.com is 'function' : not all control paths return a value. The specified function can potentially not return a value. I have included any and all sources to my professor, in my code. Can anyone explain this to me a little more in layman's terms??

My code is:

#include <cstdio>
#include <string>
#include <cstdlib>
#include <iostream>
#include <fstream>
using namespace std;


/*Create phone book entry structure.*/
typedef struct pbentry {
	char lastname[16];
	char firstname[11];
	char phone[11];

} 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)
{
	#pragma warning(disable : 4996)

	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("***** Yellow Book 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);
			
			/*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) {
			
			/*If skipped:*/
			if (strcmp(e, "s") == 0) {
				/*Confirm node edit.*/
				printf("Record edited successfully.\n\n");
				/*Return revised tree.*/
				return p;
			}
			
		}
		/*If phone number is to be changed:*/
		else {
			/*Change phone number.*/
			strcpy(p->data.phone, num);
			
			/*If skipped:*/
			if (strcmp(e, "s") == 0) {
				/*Confirm node edit.*/
				printf("Record edited successfully.\n\n");
				/*Return revised tree.*/
				return p;
			}
			
			}
	}
	}
	/*If entry is not found:*/
	

/*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);	
	}
	/*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);
		print_tree(p->right);
	}
}

Take a look a this function

struct tree_node * edit_node (struct tree_node *p, char l[], char f[]) {

The prototype suggests that your edit_node should return a value of type struct tree_node*

You have a if .. else if condition throughout the function, so if none of the conditions match, then you are not returning any value back to the calling function.

You need to fix that. You could set a default value to be sent back, which could be NULL suggesting that no node has been edited ?

Fixed that. Thanks Stilllearning, I had deleted it.
New problem has risen when I try to delete or edit, I get an Just-in-time Debugger error.
An unhandled win32 exception occurred in Binary search tree.exe[1092]. Does anyone know what I have doen wrong and how to fix this. Thanks in advance.

Its probably a segmentation fault of some sort. I cannot say what it is just glancing at your code. You may want to put some debug print statements or breakpoints in your code to try and narrow down the area where its throwing the exception.

Ok, started debugging and came up with this:

> msvcr80d.dll!strcmp(unsigned char * str1=0x00000000, unsigned char * str2=0x0012fc50) Line 83 Asm
Binary Search Tree.exe!delete_node(tree_node * p=0x00000000, char * l=0x0012ff08, char * f=0x0012fef4) Line 181 + 0xd bytes C++
Binary Search Tree.exe!delete_node(tree_node * p=0x00365708, char * l=0x0012ff08, char * f=0x0012fef4) Line 183 + 0x14 bytes C++
Binary Search Tree.exe!delete_node(tree_node * p=0x00365698, char * l=0x0012ff08, char * f=0x0012fef4) Line 183 + 0x14 bytes C++
Binary Search Tree.exe!delete_node(tree_node * p=0x00365628, char * l=0x0012ff08, char * f=0x0012fef4) Line 183 + 0x14 bytes C++
Binary Search Tree.exe!main() Line 88 + 0x11 bytes C++
Binary Search Tree.exe!__tmainCRTStartup() Line 586 + 0x19 bytes C
Binary Search Tree.exe!mainCRTStartup() Line 403 C
kernel32.dll!7c817067()
[Frames below may be incorrect and/or missing, no symbols loaded for kernel32.dll]
Any Clues, anyone?? Lost on this.

In delete_node() you need to check whether your tree node "p" is NULL or not before proceeding to do the strcmp. Otherwise trying to access p->data will throw an exception.

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