This code is supposed to put numbers into a linked list in ascending order. This is one function of my program that takes keyboard input(int x) from the user of the program.
node* insert(node *head, int x)
{
node *newPtr;
node *prePtr;
node *currentPtr;
newPtr = malloc(sizeof(node));
if(newPtr != NULL){
newPtr->value = x;
newPtr->next = NULL;
prePtr = NULL;
currentPtr = head;
while(currentPtr != NULL && x > currentPtr->value){
prePtr = currentPtr;
currentPtr = currentPtr->next;
}
if(prePtr == NULL){
newPtr->next = head;
head = newPtr;
}
else{
prePtr->next = newPtr;
newPtr->next = currentPtr;
}
}
}
int main(void)//calling input function in main
{
node *head = NULL;
int x=0;
while(x!=-1){
printf("?: ");
scanf("%d", &x);
head=insert(head,x);
print(head);
printf("\n");
}
return 0;
}
//It seems to only put a few numbers in, then it resets
The main() function asks for a numerical input, and sends that input into the insert function which is supposed to put the numbers in ascending order. Sample output:
$ gcc prelab2.c
$ ./a.out
?: 4
4 -> NULL
?: 3
3 -> 4 -> NULL
?: 9
3 -> 4 -> 9 -> NULL
?: 7
3 -> 4 -> 7 -> 9 -> NULL
?: 2
2 -> 3 -> 4 -> 7 -> 9 -> NULL
?: -1
There is only a small mistake. In main() method
head=insert(head,x);
your Insert method return nothing (NULL). so your head is never changed it is always NULL;
return head;
Just return head in insert method and it will work fine.
Try the following changes it should work fine.
node* insert(node *head, int x)
{
node *newPtr;
node *prePtr;
node *currentPtr;
newPtr = malloc(sizeof(node));
if(newPtr != NULL)
{
newPtr->value = x;
newPtr->next = NULL;
// check if the linked list is empty add the node directly and return
if(head == NULL)
{
head = newptr;
return head;
}
else
{
currentPtr = head;
while(x > currentPtr->value && currentPtr->next != NULL)
{
currentPtr = currentPtr->next;
}
// make the new node point where current next is pointing
newPtr->next = currentPtr->next;
// make the current point to new node
currentPtr->next = newPtr;
}
return head;
}
else
return NULL; // signifying malloc failed
}
EDIT: corrected the code missed out a condition check while copying
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