Sorted Linked List in C

This code is a sorted linked list in C. I was written for part of my PhD for keeping track of nodes in a Contiki OS. The code here is in it's general form. I am no expert programmer, as the code will show, but it works, which is more than many others I could find.

[[Media:M1GEO_SortedLinkedList_C.tar.gz|Source Code for Sorted Linked List in C]]

// George Smart // http://www.george-smart.co.uk/ // // Linked List example // the list element node structure. Add more stuff if you want to. struct list_el { unsigned int id;			// ID number struct list_el * next;			// link pointer (where the next element is) }; // this allows us to refer to the above structure as a node. typedef struct list_el node; // This defines *head as our top element. This allows us to find our // begining element in the linked list. node *head; // This function takes an ID and adds it to a linked list, creating a new // list or updating an existing ID if it exists. void addNode(unsigned int id) { node *curr, *new; // Create and setup our new link new = (node *)malloc(sizeof(node)); if (new == NULL) { printf("Memory not available to create link. Exiting.\n"); exit (EXIT_FAILURE); } 	new->id 				= id; // If Head is NULL, the list doesn't yet exist, so we create one. if (head == NULL) { head = new; new->next = NULL; return; } 	// does our new element go before the first one? if (new->id < head->id) { new->next = head; head = new; return; } 	// if our element goes in the middle, this code will scan through // to find out exactly where it belongs. curr = head; // start at the begining node. while ( (curr->next != NULL) ) { if ((new->id < curr->next->id)) { if((new->id > curr->id)) { // this inserts the new node into the middle if 				// it ID doesn't already exist in the list new->next = curr->next; curr->next = new; return; } else { // This section happens if the node DOES already exist // In a real program you would update the nodes other // data in this section. free(new); // get rid of 'new', we don't need it. return; } 		} 		curr = curr->next; // move to the next node. } 	// if we still haven't found the place, add at the end. //check if it's a dupe of the last element or not if (curr->id == new->id) { // if it's the same don't do anything, because the node already // exists. In a real program you would update the nodes other // data in this section. return; } else { // else add the new element on the end. curr->next = new; new->next = NULL; return; } } void delNode(int a) { int done = 0; node *curr, *prev; curr = head; // If we try and delete a node before the list exists, we'd get SIGSEGV if (head == NULL) { //printf("Couldn't remove node ID %d. List doesn't exist!\n", a); return; } 	// does our first element need to be removed? If yes, do it. if (head->id == a) { free(head); head = head->next; done = 1; return; } 	// find where the node to be deleted exists. Notice we run ahead one // node, so we don't loose the pointer to the one before the deletee while ( (curr->next != NULL) ) { if (curr->next->id == a) { prev = curr->next; free(prev); // get the memory back curr->next = prev->next; // short reference to prev done = 1; } 		if (curr->next != NULL) { curr = curr->next; //only move on if it is safe. } 	} 	// if you're interested in verbose, this well tell you if it couldn't // find what you wanted to delete. Useful for testing. if (done == 0) { //printf("Nothing done. Couldn't find node ID %d\n", a); } } // This code just loops through the entire list printing out the data. void showNodes { node * temp; printf("Printing List:\n"); temp = head; while(temp) { printf("%d\n", temp->id); temp = temp->next ; } } // The main program loop int main { head = NULL; // set head to NULL, symboling no list existing yet. int i = 0; // add nodes 5-10. for (i=10;i<=20;i++) { addNode(i); } 	addNode(5);		// add an element out of order at begining addNode(25);		// add an element out of order at end addNode(17);		// add an element out of order, creating duplicate // node this program updates same number. showNodes; delNode(5);		// remove the first element delNode(15);		// remove the a middle element delNode(25);		// remove the last elelemt delNode(30);		// remove a number that isn't present. showNodes; return 0; }
 * 1) include 
 * 2) include 