CS 101  Lab Activity 8

Objectives:

• Use your knowledge of select statements, arrays, loops and string functions to write code for the Hangman game (Part 2)and to write a program that computes statistics on the words in a text file (Part 3).

• Understanding function return values and input parameters.

• Understand arrays of characters, arrays of strings to decrypt an encrypted message.

• This lab is to be worked in groups.

References

• Lectures 13/14 on loops, lecture 15 on arrays and lecture 16 on functions.

Part 1: Nested Loops

Answer questions 1-3 on the answer sheet.

Part 2: Hangman Game

1. Requirements Specification (Problem Definition)

• The user selects between options : Hard, Moderate and Easy
• The computer assigns the maximum number of guesses based on selected option
• The computer picks a word from an available word list
• The user is allowed to guess the letters in the word, one at a time
• If a guessed letter is indeed in the word, its exact location in the word will be shown
• Otherwise the user loses a guess
• Only a limited number of guesses is allowed - a correct guess is not counted
• The user keeps guessing until:
  • The complete word is shown (the user wins) OR
  • The user runs out of guesses (the computer wins)

Open up a unix terminal  and make a new directory named lab8.

cd

mkdir lab8

cd lab8

Download the files named hangdemo and hang.c .
Run the demo program hangdemo (At the Unix prompt type: hangdemo).

./hangdemo

Watch how the demo program works. You're going to write a similar program. If you have a problem running this program then at the Unix prompt type

chmod u+rwx hangdemo 

2. Analysis---Refine, Generalize, Decompose the problem definition

  We will give you the skeleton code in hang.c that includes the steps that you need to go through in your program (see step 4. Implementation below). But of course, you can start to write the program from scratch if you prefer. You should consider using the following functions in your program:

• rand() - to generate random numbers
• strlen() - to determine the length of a string
• strcpy() - to copy a string to another
• strcmp() - to compare two strings
• tolower() - to convert a character to lowercase (if it is an uppercase letter)

3. Design---Develop Algorithm

The complete flow-chart for the program is shown below.

4. Implementation --- Write the "Program" (Code)

Use the flow chart above and open gedit to type your code in the file named hang.c that you downloaded.

5. Run the code

After you've completed your program, then answer questions #4 and #5 on the Answer sheet.

Part 3: String Matching and Statistics

1. Requirements Specification (Problem Definition)
In this part of the lab, you will learn how to call a C function and pass input arguments to parameters.  You will also code a couple simple C functions which will allow you to match strings, and calculate simple statistics.

Download three files named lab8.c, lab8.h and shelterfromthestorm.txt into your lab8 directory.

• Use gedit to open the skeleton source file 'lab8.c' as your starting point.

• When compiling, name your executable file 'lab8' by using the -o switch, e.g. at the Unix prompt type,
  > gcc lab8.c  -o  lab8

• and if you don't have any error messages, run your program by typing,
  > ./lab8

Note: not all the details of the code are listed in the steps below. For example, if you code a loop that uses the variable 'i' then it is assumed that you know that you must declare this variable in your function.

You will not have to write any prototypes since this has already been done for you.
Use gedit to open the file 'lab8.h' (do not change anything in this file) and notice that the prototypes for all functions in this lab have already been typed for you.

Why should you use the lab8.h file?
Many practical programs consist of more than one function, and each might be coded in different .c files. To make sure that the entire program shares a consistent set of functions (names of functions, data type of the input parameters etc) and data structures, we create a header file (a .h file) and put all the function prototypes, as well as commonly used constants in that file. This is the case for MP2. In this lab, we'll use a header file lab8.h to give you practice in reading .h files containing prototypes and constants.

Since C (and Unix) is case sensitive, it is best to copy all the function prototypes from the .h file to your actual .c file to start implementing the functions. That will ensure that you are using exactly the same function names (e.g. showMenu, not showmenu nor ShowMenu), and you have the data type for each parameter as well as the return value ready. We have already copied the prototypes from the lab8.h file into the lab8.c file for you.

2. Analysis---Refine, Generalize, Decompose the problem definition

The input for this program will come from two sources. Input will come from a keyboard. We will display a menu and request an integer response. The scanf function will be used to read the users response. We will also read words from a file. To do this we will use a new function named fscanf. The fscanf fuction requires the use of pointers. Since we haven't covered pointers in lectures yet all code for the fscanf function has been written for you already.


3. Design---Develop Algorithm

The program can be broken into the following steps :

1. Complete the code for the function showMenu that shows the main menu, and returns any input from the user. The following is our menu:
   
   Main Menu
   ----------
   1. Input words
   2. Display words
   3. Search for an exact match
   4. Calculate the average length
   0. Exit

   Please enter a choice :
   
   You will need to add a scanf to read the response the user types from the keyboard.

2. Save and compile your code.
   gcc lab8.c  -o  lab8
   
   
   Run your program.
   ./lab8
   At this point you will see a menu but since you haven't completed the switch statement your code will only respond to user response 0.

3. The first function is inputWords, which reads words from a file into an array named words. 

The function inputWords returns the count of the number of words read, so you will have to modify the return statement in the inputWords function.
Next, modify the main function. In the swtich statment, add a case for 1, i.e. case 1:  and call inputWords  (note that this function requirest that you pass the words array as an input argument)  and assign the value that inputWords returns to the variable named count in main. Don't forget to add a break; statement.



4. The second function displayWords has been coded for you. Update main to call displayWords in the switch statement for case 2: .




5. Save, compile and run your program now. Select menu option 1 and next option 2. If you get an infinite loop (possibly by forgetting the break in the switch statement) type Control-c at the keyboard. You may have to type Control-c MANY times. You should see a list of words, the last eleven being,




Come
in
she
said
I'll
give
you
shelter
from
the
storm.




 


6. The third function is exactMatch. The function exactMatch counts how many times a certain target word appears. The user will provide the target word. The input parameters are count and words. Do not declare these again in your code.

• Declare a local integer num , which will will hold the number of matches. Initialize it to 0.

• Declare a variable named target of data type string.

• Prompt the user to enter a target string, with which he/she wants to search for an exact match.

• Use a single scanf statement to read the string into target.

• Write a for loop to search for exact match between the entered words and a target string. To compare two strings, use strcmp function declared in string.h. The strcmp function returns 0 if two strings are the same, and non-zero value otherwise. If there is an exact match, increment a local counter num. If you use an index variable in your for loop say i, (for refrencing words[i] then make sure to declare this variable.

• After the for loop, print out the number num of exact matches using a printf statement. You can remove the comments and complete the call to the printf function.



Update main to call exactMatch the switch case 3: statement.



Save, compile and run your program and test if this option works correctly.When you run your code make sure to select option 1 before you select other options since you need to first read in the array of strings from the file.





7. The last function is calculateMeanLength. This function calculates the average length of all the words in the file shelterfromthestorm.txt .

   • Declare a local double variable total , which will calculate the sum of lengths. Initialize it to 0.0 . Note that it should be declared as double (not integer.)

   • Write a for loop to calculate the sum of of word lengths. For each interation, add the length of each string. To get the length of a string, use strlen function declared in string.h. The strlen function returns the length of the string.
     For example,

         for(i=0;i<count;++i)
             total += strlen(words[i]);

   • After the for loop, use the printf function to print the average. (Uncomment the printf statement and complete it).To calculate the average length, which equals the total divided by the variable count, which stores the number of entered strings.

   
   Update main to call calculateMeanLength in the switch case 4: statement.

   
   4. Implementation --- Write the "Program" (Code)
   Use the pseudo-code above and open gedit to type your code in the appropriate function in the file named lab8.c that you copied from the directory  /class/cs101ta/public_html/labs/lab8 .

   
   5. Run the code
   Save, compile and run your program and test if this option works correctly.
   
   Now it's time to fill in the blanks on your answer sheet.
   
   
   Answer questions #6, #7, #8 on the answer sheet.

Notes:


• To store the words ( strings), we have declared (in main) a 2-dimensional array of characters named words. The code in lab8.h shows that the user must not enter more than 1000 words, and each word is at most 64 letters. For your convenience, we defined MAX_COUNT and MAX_LENGTH in lab8.h. (Why is MAX_LENGTH defined as (64+1) instead of 64?)

• We are using a variation of the scanf function called fscanf (file scanf) to read data from a file named "shelterfromthestorm.txt". We will NOT have to use Unix redirection (<) .

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The End!