Lab 2: Sorting and GDB

CS 2401 
Lab 2: Sorting and GDB

For this lab I have provided a little class that stores numbers and keeps them in order. The way
it does this is with a “reverse bubble sort,” one that starts at the end of the array and works its
way to the beginning. The advantage of this is that the new numbers are added to the back end
of the array. (The spot always represented by the variable used.) When a new number is added
the bubble sort can make one pass through the array and the new number will drop in place.
The problem is that the bubble sort is crashing, and I need you to diagnose why that is
happening and to fix it. I want you to do this using gdb. I will also need you to write the
load_from_file and write_to_file member functions, as well as a main that drives the program.
Start by downloading the files I have provided on Blackboard.
You will find a little class that stores numbers in an array. Some of these functions have been
written for you, and some are left for you to write yourself.
Your jobs are to:
• Write the implementations for the load_from_file and save_to_file functions.
• Write a main that asks the user for the name of their file. Remember you can read the filename
into a string and then use the .c_str() function to use that string in an open command:
o ifs.open(filename.c_str());
The main then:
• loads the array from the file into a NumList object
• Calls the b_sort function on the NumList
• Writes the sorted numbers out to the screen, using the see_all function.
Here there is a problem. Something goes into an infinite loop. To find this you are going to use
gdb. (I have provided a data file called smaller.dat, so that you will not have to walk through so
much code.) Here are the steps:
• Compile with the –g option (g++ -g *.cc)
• Type gdb ./a.out
• Type break main
• Type run
• Start hitting n to walk through the code
• When you get to the call of a member function you want to “step into” hit s
• Continue hitting n
Using this method, try to find the error in the code that I gave you, and then correct it. When
you do, recompile everything and test it. You should see a sorted list of numbers on the screen
for either the larger.dat or the smaller.dat file.
Open your main again, and have it ask the user to type in three of their own numbers, which
will be inserted into the list. Using the string member function find (which returns the location
of a substr within the string) and the insert function (which will insert a substring at the position
sent as its first argument), modify the filename, so that the characters “sorted” are inserted
before the dot. (This means that “larger.dat” becomes “largersorted.dat” and “ebenezer.txt”
becomes “ebenezersorted.txt” ). Then have the main write the number array out to that file.
After you have successfully compiled all of this run it on the larger.dat file and insert the
numbers 106, 237 and 45,701.
Submit to your source code and sorted data file on Blackboard.