using while in recursive function - c

Question

to display a linked list, I am using a recursive function. which was running infinite loop thanks to while loop.
when replaced with "if" the program worked without any issues.
looking for expert opinion on usage of
while
inside a recursive function.
recursive function with while
int display(node *curr){
if((curr->next != NULL) ){ //<--replace "if" with "while" and it runs infinite loop
printf("%d :: ",curr->data);
display(curr->next);
}
return 0;
}
complete code with create and display function
#include<stdio.h>
#include<unistd.h>
#include<string.h>
#include<stdlib.h>
struct node {
int data;
struct node *next;
};
typedef struct node node;
int create(node *head);
int display(node *head);
int main(int argc, char *argv[]){
int ch,n=0;
node *head,*tail,*current;
head=(node*)malloc(sizeof(node));
create(head);
printf("\n");
display(head);
return 0;
}
int create(node *curr){
int data;
node *next;
printf("Enter the Data Value (Enter -1 to Finish): ");
scanf("%d",&data);
curr->data=data;
if(data == -1)
{
curr->next=NULL;
//return curr;
}
else
{
curr->next=(node*)malloc(sizeof(node));
create(curr->next);
}
return 0; }
int display(node *curr){
if((curr->next != NULL) ){
printf("%d :: ",curr->data);
display(curr->next);
}
return 0; }

Answer 1

The reason why you cannot use the while(curr->next != NULL) loop to index through and print the list is because for each call of the function display(), the value of curr->next is constant. This seems like it will successfully print the data in your linked list, and then infnitely print the second to last data point, as the comparison for the last data point will continually fail.
as suggested by Ritwick Dey, using
int display(node *curr)
{
while (curr)
{
printf("%d",curr->data);
curr = curr->next;
}
}
should work for you; by changing the pointer of the current node, you modify the conditional of the while loop every iteration. a value of NULL will cause this check to fail, so you can print the final data point without issue. this implementation has the added benefit of avoiding the cost of the recursive function call.

Answer 2

Though the question is not fully clear, I think you are asking why the code is working after changing the 'while' statement to 'if'. The explanation is below:
1.)You are not advancing your next pointer.
2.)Let's assume you have advanced your next pointer even then your code will run infinitely.
A simple dry run should be enough for this:
Let's take an example suppose your Singly link list of positive integers looks like this:
8-->9-->7-->NULL
Then following will be your recursion tree which illustrates on which condition your code is running infinitely.
display(8)
while(8->next)->display(9)
        while(9->next)->display(7)
               while(7->next)->display(NULL)--return
After returning from display(NULL) this will run infinitely for this case: while(7->next)---->display(NULL) and it will continue to loop around the same.
The correct function to display the link list is already pointed out in the Ritwick's answer.

Answer 3

int display(node *curr)
{
while (curr)
{
printf("%d",curr->data);
curr = curr->next;
}
}
Simple......

Answer 4

You get an infinite loop because you never advance the in the list, that's: l = l->next(); so, you never reach null