segmentation error in ubuntu - c

Question

Please tell me why the segmentation error is there in my program there is no error .
I also tried to debug it but it never goes inside the for statement.
#include<stdio.h>
#include<malloc.h>
struct node
{
int data;
struct node* link;
} *start;
main()
{
int i,n,m;
start=NULL;
printf("enter the number of nodes you want");
scanf("%d",&n);
for(i=0;i<n;i++)
{
printf("enter the element you want to insert");
scanf("%d",&m);
create_list(m);
}
}
create_list(int data)
{
struct node *q,*temp;
temp=(struct node *)malloc(sizeof(struct node));
temp->data=data;
temp->link=NULL;
if(start==NULL)
start=temp;
else
{
while(q->link!=NULL) q=q->link;
q->link=temp;
}
}

Answer 1

You forgot to initialize q before using it:
q = start;
while(q->link!=NULL)

Answer 2

1.You haven't initialized q in create_list() and used it -
while(q->link!=NULL)
Intialize q=start; before this loop.
2.Also free the allocated memory for temp in function.
3.main() should be int main(void) and what is type of create_list? Declare its prototype before main.

Answer 3

In the function create_list local pointer q was not initialized
struct node *q,*temp;
^^^
However it is accessed in the loop
while(q->link!=NULL)
I think you mean the following
else
{
q = start;
while ( q->link != NULL ) q = q->link;
q->link = temp;
}
Take into account that the function should be declared before its usage. Place it declaration for example before main. And its return type shall be void and specified explicitly. Also function main shall have return type int.
For example
void create_list( int data );
int main( void )
{
//...
And it is a good idea to free all dynamically allocated memory before exiting the program.
Also header <malloc.h> is not a standard C header. You should use <stdlib.h> instead.

Answer 4

After all suggestions from the above it will be clearly in the future if you try to show some work of your clear codding and to respect the minimum standard.
Here is a way of how should be looking your code:
#include<stdio.h>
#include<stdlib.h> /* You need stdlib not malloc */
void create_list(int data); /* If you don't declare your function the compiler doesn't know nothing about create_list */
struct node{
int data;
struct node* link;
}*start;
int main(void){ /* Here return type of main is int and if no arg needed should be used void */
int i,n,m;
start=NULL;
printf("enter the number of nodes you want");
if((scanf("%d",&n)) != EOF) /* always check scanf's return */
for(i=0;i<n;i++){
printf("enter the element you want to insert");
if((scanf("%d",&m)) != EOF) /* here the same: always check scanf's return */
create_list(m);
}
return 0; /* return of main should be 0 or one of the following: EXIT_SUCCESS or EXIT_FAILURE, but 0 will be ok because it is standard*/
}
void create_list(int data){ /* here should be explicit what kind of function is */
struct node *q,*temp;
temp=(struct node *)malloc(sizeof(struct node)); /* if you allocate memory dynamically ..... */
temp->data=data;
temp->link=NULL;
if(start==NULL){
start=temp;
}else{
q = start;
while(q->link!=NULL){
q=q->link;
q->link=temp;
}
}
free(temp); /* .....then always free it */
}