Inserting at the end of queue in C - c

Question

I am trying to insert node at the end of queue and facing below error . This is simple fundamental error while compiling the code but making my life hard.
#include<stdio.h>
#include<stdlib.h>
typedef struct UNIX {
char str[20];
struct UNIX *next;
}examp;
examp *head=NULL;
int insert_last(char *s)
{
examp *new,*slide;
slide=head;
new = (examp *)malloc(sizeof(examp));
if(!new)
return(EXIT_FAILURE);
while(slide->next!=NULL)
slide=slide->next;
slide->next=new;
new->str=s;
new->next=NULL;
if(head==NULL)
{ head=new;
return 1;
}
return 1;
}
void display (void);
int main()
{
insert_last("hello ");
insert_last("how ");
insert_last("have ");
insert_last("you ");
insert_last("been ");
insert_last("! ");
display();
}
void display(void)
{
examp *slide;
slide=head;
while(slide->next!=NULL)
{ printf("%s ",slide->str);
slide=slide->next;
}
}
Error :stack_queue.c:27:10: error: assignment to expression with array type
new->str=s;
Update : Using strncpy reolved the error , but code is not working as expected and stopping unexpectedly.

Answer 1

You can't assign to a static array like that. Consider using strcpy or strncpy to copy the contents of the character string instead.

Answer 2

You cannot assign a string to an array! An array have its own memory, you can write or read elements in the array, but cannot assign an address.
You can eventually copy the string s contents to the array:
strncpy(new->str, s, 19);
new->str[19] = '\0'; //Close the string in case of overflow.
We used strncpy to limit the copied characters to the array size (19 chars + the ending '\0').

Answer 3

You can try it. Only replace in new->str=s; to strcpy(new->str, s); (ie. s will be copy in to new->str)
#include<stdio.h>
#include<stdlib.h>
typedef struct UNIX {
char str[20];
struct UNIX *next;
}examp;
examp *head=NULL;
int insert_last(char *s)
{
examp *new,*slide;
slide=head;
new = (examp *)malloc(sizeof(examp));
if(!new)
return(EXIT_FAILURE);
while(slide->next!=NULL)
slide=slide->next;
slide->next=new;
strcpy(new->str, s);
new->next=NULL;
if(head==NULL)
{ head=new;
return 1;
}
return 1;
}
void display (void);
int main()
{
insert_last("hello ");
insert_last("how ");
insert_last("have ");
insert_last("you ");
insert_last("been ");
insert_last("! ");
display();
}
void display(void)
{
examp *slide;
slide=head;
while(slide->next!=NULL)
{ printf("%s ",slide->str);
slide=slide->next;
}
}

Answer 4

As already stated you will have to use strcpy (or strncpy) in order to assign the string.
Asides from that I wanted to mention two things:
Do not forget to free your memory allocated by malloc. Create a method to free a single node (examp) then you can also provide a method to destroy the whole list.
I would suggest to rename the variable new to avoid confusion (pure C compiler may deal with it, but C/C++ compiler will most likely get into trouble).
Considering your update:
Take a look at the following line
while(slide->next!=NULL)
At this time slide does not even exist (it is NULL), still you perform an operation on the pointer. This is the reason why the program crashes.

Answer 5

Your error is in the first call insert_last("hello "):
int insert_last(char *s)
{
examp *new,*slide;
slide=head;
new = (examp *)malloc(sizeof(examp));
if(!new)
return(EXIT_FAILURE);
while(slide->next!=NULL)
slide=slide->next;
when you call it first time, head is NULL, so slide becomes NULL, but you don't check it, and call it in
while(slide->next!=NULL)
Here slide is null for the frst function call