C Programming MIT Problem SET5 - Solutions

Massachusetts Institute of Technology
Department of Electrical Engineering and Computer Science

6.087: Practical Programming in C

IAP 2010

Problem Set 5 – Solutions
Pointers. Arrays. Strings. Searching and sorting algorithms.

Out: January 19, 2010. Due: January 20, 2010.

Problem 5.1
In this problem, we continue our study of linked list. Let the nodes in the list have the following
structure
struct node
{
i n t data ;
struct node ∗ next ;
};

Use the template in Lec06 (slides 35,36) to add elements to the list.

(a) Write the function void display(struct node∗ head) that displays all the elements of the list.

(b) Write the function struct node∗ addback(struct node∗ head,int data) that adds an element to the
end of the list. The function should return the new head node to the list.

(c) Write the function struct node∗ find(struct node∗ head,int data) that returns a pointer to the
element in the list having the given data. The function should return NULL if the item does
not exist.

(d) Write the function struct node∗ delnode(struct node∗ head,struct node∗ pelement) that deletes the
element pointed to by pelement (obtained using find). The function should return the up­
dated head node. Make sure you consider the case when pelement points to the head node.

(e) Write the function void freelist (struct node∗ head) that deletes all the element of the list. Make
sure you do not use any pointer after it is freed.

(f) Write test code to illustrate the working of each of the above functions.

All the code and sample outputs should be submitted.




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, Answer: Here’s one possible implementation:
#include<s t d i o . h>
#include<s t d l i b . h>

struct node
{
i n t data ;
struct node ∗ next ;
};

/∗
@function n a l l o c
@desc a l l o c a t e s a new node e l e m e n t s
@ r e t u r n s p o i n t e r t o t h e new e l e m e n t on s u c c e s s , NULL on f a i l u r e
@param data [ IN ] pa y l o a d o f t h e new e l e m e n t
∗/
struct node ∗ n a l l o c ( i n t data )
{
struct node ∗ p=( struct node ∗ ) m a l l o c ( s i z e o f ( struct node ) ) ;
i f ( p!=NULL)
{
p−>next=NULL;
p−>data=data ;
}
return p ;
}

/∗
@function addfront
@desc adds node t o t h e f r o n t o f t h e l i s t
@param head [ IN ] c u r r e n t head o f t h e l i s t
@param data [ IN ] data t o be i n s e r t e d
@return updated head o f t h e l i s t
∗/
struct node ∗ a d d f r o n t ( struct node ∗ head , i n t data )
{
struct node ∗ p=n a l l o c ( data ) ;
i f ( p==NULL) return head ; /∗ no change ∗/
p−>next=head ;
return p ;
}

/∗
@function display
@desc d i s p l a y s t h e nodes i n t h e l i s t
@param head [ IN ] p o i n t e r t o t h e head node o f t h e l i s t
∗/
void d i s p l a y ( struct node ∗ head )
{
struct node ∗ p=NULL;
p r i n t f ( " list :" ) ;
f o r ( p=head ; p!=NULL; p=p−>next )
p r i n t f ( "%d " , p−>data ) ;
p r i n t f ( "\n" ) ;
}

/∗
@ f u n c t i o n addback



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