zach.c

#include <stdio.h>

struct entry
{
    int             value;
    struct entry    *next;
};

void insertEntry (struct entry *newPtr, struct entry *beforePtr)
{
    newPtr->next = beforePtr;
    beforePtr = newPtr;
}

void insertAfter(struct entry * newEntry, struct entry * targetEntry) {
	newEntry->next = targetEntry->next;
	targetEntry->next = newEntry;
}

int main (void)
{
    void insertEntry (struct entry *newPtr, struct entry *beforePtr);
    struct entry n1, n2, n3, n2_3;
    struct entry *listPtr = &n1, *entryPtr = &n2_3;
    n1.value = 100;
    n2.value = 200;
    n3.value = 300;
    n2_3.value = 250;

    /*set up linked list */
    n1.next = &n2;
    n2.next = &n3;
    n3.next = 0;

    printf ("The linked list before adding another entry is:\n");

    while (listPtr != (struct entry *) 0 )
    {
	printf ("%i\n", listPtr->value);
        listPtr = listPtr->next;
    }

    printf ("The linked list after adding another entry is:\n");

    // insertEntry (entryPtr, n2.next);
	insertAfter(entryPtr, &n2);

    /*reset to start of list */
    listPtr = &n1;

    while (listPtr != (struct entry *) 0 )
    {
	printf ("%i\n", listPtr->value);
        listPtr = listPtr->next;
    }

    return 0;
}