CSC35 Lab 7 -Wacky Words Solved

Wacky Words

Overview

As kids we all got to play fun word games. Of course, we started with the classic See N’ Say®, but eventually we moved on to other fun games such as MadLibs®.

Often, the player would enter various nouns, verbs. These words would then be inserted into a story. Because the player didn’t know the context of the words, the resulting story can be silly, nonsensical, or simply weird.

For this lab, you are going to a very basic form of this type of game. You will have the player input three words and your program will print out a wacky sentence. The sentence is completely up to you!

Sample Run

The following is a sample run of the program. The user’s input is
printed in blue. The data outputted from your buffers is printed in red. Don’t use this (rather boring) sentence in your program. Use your own!!!!

Part 1 – Using Your Last Lab

Like that last lab, you aren’t allowed to use that handy-dandy CSC35.o library. Instead, use will reuse some of your from Lab 6 to make this lab much easier.

You created a subroutine that was used to print a string to the screen. The name was up to use – as was the two registers that you used. All that being said, if your subroutine was named “MyExcellentWrite” and used register rax (for the address) and rbx (for the length), calling it would look like this:

Let’s make a copy of your last lab and modify it. Type the following at the UNIX prompt. I’m assuming your Lab 6 is named “lab6.s”. If it is something else, use that name:

 cp lab6.s lab7.s

Presto! You copied the file. Open and edit this one.

Part 2 – Your Read Subroutine

Running the UNIX Kernal call to read a string is pretty much like writing one. To create an empty buffer, you can use the .space directive. It will create specified number of bytes in memory.

You will call the UNIX “read” command with the buffer address and the maximum size of the buffer. UNIX will return the number of characters that the user entered in the %rax register. This is the length of the string. Also note, this length includes the new line. You should subtract one.

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mov $Hello, %rax
mov $23, %rbx
call MyExcellentWrite

3 So, let’s assume – once again – that you will write a subroutine called “MyAwesomeRead” and it uses the rax

register (for the buffer), and rbx (for the maximum number of character). Calling it would look like this:

Your subroutine will return the number of characters read in a register. This this example, it was rbx. Your main program will need to save this value – you will need it later.

Part 3 – The Game

This lab has several parts you need to get working before continuing on. If you attempt to write the entire program at one time, it will be nearly impossible to find bugs. If you try to write it all at one time, I might (during the lab) simply recommend you start over.

Remember: incremental design!

1. First, you need to be able to read data from the keyboard.
2. Now see if you can print off the buffer you just filled from the keyboard. Make sure to use the length of the string in the buffer rather than the entire buffer.
3. Working? Excellent! Now see if you can do it with another variable. You need a second buffer and variable to hold the number of characters UNIX read.
4. Now let’s see if you can make your program print the entire sentence on one line.

Requirements

You must think of a solution on your own. Looking at another student’s solution may result in a zero on this assignment. The requirements are as follows:

1. Read in three words from the player.
2. Prompt the player each time.
3. Print the sentence to the screen. This must be your creation! Use your imagination! 4. Show one your classmates your creation!

UNIX Commands

Editing

Folder Navigation

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File Organization

Just in case you need it…

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The following is the UNIX call for write. You used this in Lab 6.