Adding node to a linked list - c

Question

So I'm creating a linked list in C and adding some nodes to it that contain information. I have an if else statement where I create the linked list's head and then add nodes to it. The problem is that when I add a new node I seem to lose the old one. Not sure why this is happening or how to fix this.
Edit: I have made some updates to make it a runnable program.
#include<stdio.h>
#include<string.h>
#include<stdlib.h>
#include<stdint.h>
#include<regex.h>
int main(int argc, char argv[]) {
int head=0, i=0;
char tempCourseID[10], tempCourseGrade[10], tempCourseCH[10];
static struct LinkedList {
char *CourseName;
char *CourseGrade;
char *CourseCreditHours;
struct LinkedList *next;
} LinkedList;
static struct LinkedList *first, *savefirst, *headlist;
first = malloc(sizeof ((*first)));
savefirst = first;
headlist = first;
for(i ; i<5; i++){
printf("Enter Course name");
fgets(tempCourseID, sizeof(tempCourseID), stdin);
printf("Enter Course grade");
fgets(tempCourseGrade, sizeof(tempCourseGrade), stdin);
printf("Enter Course credit hours");
fgets(tempCourseCH, sizeof(tempCourseCH), stdin);
//checks to see if linked list head exists
if (head == 0) {
printf("No head has been found.\n");
headlist->CourseName = tempCourseID;
headlist->CourseGrade = tempCourseGrade;
headlist->CourseCreditHours = tempCourseCH;
headlist->next = NULL;
printf("A head has been created\n");
printf("A node has been added\n");
head = 1;
} else {
printf("Ahead already exists\n");
first = malloc(sizeof ((*first)));
first->CourseName = tempCourseID;
first->CourseGrade = tempCourseGrade;
first->CourseCreditHours = tempCourseCH;
first->next = NULL;
savefirst->next = first;
savefirst = first;
printf("A node has been add\n");
head = 1;
}
}
while (headlist != NULL) {
printf(" %s ", headlist->CourseName);
printf(" %s ", headlist->CourseGrade);
printf("%s \n", headlist->CourseCreditHours);
headlist = headlist->next;
}
return 0;
}

Answer 1

You have char tempCourseID[10] and char* CourseName
It is legal to use CourseName = tempCourseID; however tempCourseID is temporary, and so the string will be lost soon. In this case we need to allocate separate memory for CourseName, and then copy the value from tempCourseID
Use instead
CourseName = malloc(strlen(tempCourseID) + 1);//add +1 for null-character
strcpy(CourseName, tempCourseID);
//or
CourseName = strdup(tempCourseID)//shortcut!
There are problem with the linked list. You have too many variables with similar names. A linked list needs only head. You can introduce a temporary variable node for adding new nodes. If you are adding nodes to the tail, then save the last node in the list, lets call it savenode
In this example I removed fgets functions and replaced it with sprintf, that's just to make it easier to run the program and debug. You can put back fgets later.
int main(int argc, char argv[])
{
struct LinkedList
{
char *CourseName;
char *CourseGrade;
char *CourseCreditHours;
struct LinkedList *next;
};
int i;
char tempCourseName[100], tempCourseGrade[100], tempCourseCH[100];
struct LinkedList *head = NULL;
struct LinkedList *node = NULL;
struct LinkedList *savenode = NULL;
for(i = 0; i < 5; i++)
{
sprintf(tempCourseName, "CourseName %d", i);
sprintf(tempCourseGrade, "tempCourseGrade %d", i);
sprintf(tempCourseCH, "tempCourseCH %d", i);
node = malloc(sizeof(*node));
node->CourseName = strdup(tempCourseName);
node->CourseGrade = strdup(tempCourseGrade);
node->CourseCreditHours = strdup(tempCourseCH);
node->next = NULL;
if(head == NULL)
head = node;
//check savenode exists
//this will be the last node (tail) in the existing list
//get it to point to our new node
if(savenode)
savenode->next = node;
//now we have a new tail
savenode = node;
}
//walk through the list
node = head;
while(node)
{
printf("%s, %s, %s\n",
node->CourseName, node->CourseGrade, node->CourseCreditHours);
node = node->next;
}
return 0;
}