CS 161 Lab 4




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Lab 4
Get checked off for up to 3 points of incomplete work from the previous lab
within the first 10 minutes of lab.
ONLY Monday Lab Students: As there was no lab on Monday ( Jan 18 ), you can
check off the lab for maximum of 10 points
Each lab will begin with a recap of last lab and a brief demonstration by the TAs
for the core concepts examined in this lab. As such, this document will not serve
to tell you everything the TAs will in the demo. It is highly encouraged that you
ask questions and take notes. In order to get credit for the lab, you need to be
checked off by the end of lab. For non-zero labs, you can earn a maximum of 3
points for lab work completed outside of lab time, but you must finish the lab
before the next lab. For extenuating circumstance, contact your lab TAs and
In this lab, you can form a group of 2-3 individuals. You must be checked off
together as a group at the end of the lab. Although you perform tasks as a group,
ensure thatyou understand the work and ask questions to TAs as needed.
(1 pt) Review from Lab #3
1. Vim commands:
a. How do you auto indent your program?
b. Explain what the following commands do:
dd, y3, p, :set cindent
(1 pt) VIM exercises
These exercises on the computer need to be repeated by each student in the pair.
This is to ensure that both students understand how to get around in Linux!!! For this part
of the lab, you will create a .vimrc file that will help you develop your C++ programs using
VIM. First, we need to create a simple .vimrc file in your home directory on the ENGR
(flip) server. vim .vimrc
In this file, you can insert the following lines so that it makes working with vim easier.
Comments are prefaced with a quotation mark, “.
filetype on
filetype plugin on
filetype indent on
autocmd FileType c, cpp
set cindent “This allows for c-like indentation
set sw=3 “Set the sw for the auto indent to 3 spaces
set number “Show the line numbers on the left
“Change the color of the text and turn on syntax highlighting
“color desert
color torte
colorscheme evening
syntax on “Turn on syntax highlighting
set showmatch “Show matching braces
set showmode “Show current mode
“When one of the chars is typed, the matching is typed and the
cursor moves left “The line below is single quotes
inoremap ‘ ”<Left>
“The line below is double quotes
inoremap ” “”<Left>
inoremap { {}<Left>
inoremap ( ()<Left>
There are many more commands you can insert in this file, and here is a reference
guide to some of these:
(2 pts) Testing and Debugging
Download the following cpp file. (Use wget command)
You must find as many bugs as possible and fix them. Some are logic errors, some are
syntax errors. Hint: there are 21 bugs in total, some are obvious, some are more
complex. Make sure you re compile and run your program after you make a single
fix to a mistake to make sure you actually fixed the mistake, didn’t introduction
new errors, and/or eliminated other errors as a result of the fix.
(1 pt) Design atoi
atoi() is a common function which takes a character and returns its decimal ASCII value.
Start by designing how this function will work. It should take any character found on the
ASCII chart ( and return the decimal value.
** Function: a_to_i
** Description: turns a character into a decimal value
** Parameters: char character
** Pre-Conditions: the input is a character
** Post-Conditions: returned the decimal value of the character
(2 pts) Implement atoi
Write the a_to_i() function based on your design. Test your function thoroughly.
Will your function properly return the decimal value of: ‘A’, ‘1’, ‘b’, ‘/’, ‘ ‘, etc.?
(1 pt) Design itoa
Similar to a_to_i(), i_to_a() takes an integer and returns the character associated
with that value. Design this function.
** Function: i_to_a
** Description: turns a decimal value into a character value
** Parameters: int decimal
** Pre-Conditions: the input is an integer
** Post-Conditions: returned the character which represents the decimal value
(2 pts) Implement itoa
Write the i_to_a() function. Test your function thoroughly. Will it return the correct
character value for 127, 65, 97, etc.? For this exercise, you can assume that the input
will not be less than 0 or greater than 127.
Show your completed work to the TAs for credit. You will not get points if you
do not get checked off!