Homework 2

Out: Tue 16 Sept 1997
Due: Tue 23 Sept 1997

Programming Assingment:

Modify your program from Homework 1 to use functions for the list operations.

Write a program which uses a linked list of characters to count the number of each character in an input stream of text. Modify the previous program, modifying the DataBox data structure to include a count field, and adding functions to search a linked list, to increment the count of an element on the linked list, and to add elements to a linked list.

The new DataBox structure is:
struct DataBox { char item ; int count ; DataBox * next ; } ;
The type of a list uses a typedef as follows:
typedef DataBox * MyList ;
The find routine has signature:
DataBox * findItem( MyList ml, char charToFind ) { /* your code here */ }
The increment count routine has signature:
void incrementCount( MyList ml, DataBox * db ) { /* your code here */ }
The add to list routine has signature:
void addToList( MyList ml, char charToAdd, int initialCount ) { /* your code here */ } ;

Using the above defined functions, the loop in the main program is:

     while ( *p!='\0' ) { 
        if ( (db=findItem(ml, *p)) != NULL ) {
           incrementCount(ml,db) ;
        } else {
           addToList( ml, *p, 1 ) ;
        }
        p++ ; 
     }

Submitting Homework:

Use the command PostIt filename to submit your homework. You will first need to set the environment variable named POSTIT (note all capital letters!) to mth220:

   setenv POSTIT mth220

Then go to the directory where your file is located, let's say it's called MyLinkedList.C, and type

   PostIt MyLinkedList.C

What will happen is that an encrypted copy will be placed in your public_html/mth220 directory. (PostIt will create this directory and give it proper permissions when you first use PostIt).

PostIt will refuse to post over an already submitted assignment. You should repost assignments by appending a version number to the name. For example, MyLinkedList.C.1. The date that the public_html/mth220 file is created is your receipt for the submission. For this reason, do not repost over a file.