CS 2110 Homework 7 Intro to C Solved

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Justin Hu, Christopher Turko, Irene Lee, Shawn Wahi, Sameer Suri, Alice Zeng
1 Overview 2
1.1 Purpose 2
1.2 Task 2
1.3 Criteria 2
2 Detailed Instructions 3
2.1 “my string.c” functions 3
2.2 hw7.c 3
2.3 hw7.h 4
2.4 Makefiles and Testing 4
3 Useful Tips 5
3.1 Man Pages 5
3.2 Debugging with GDB and printf 5
4 Checking Your Solution 6
5 Deliverables 7
6 Appendix 8
6.1 Appendix D: Rules and Regulations 8
6.1.1 General Rules 8
6.1.2 Submission Conventions 8
6.1.3 Submission Guidelines 8
6.1.4 Syllabus Excerpt on Academic Misconduct 9
6.1.5 Is collaboration allowed? 9

1 Overview
1.1 Purpose
The purpose of this assignment is to introduce you to basic C programming, building on your knowledge of assembly. This assignment will familiarize you with C syntax and how to compile, run, and debug C programs. You will become familiar with how to work with strings, arrays, pointers, and structs in C. You will understand the relationship in C between arrays and pointers, including pointer arithmetic (think about how arrays are stored in memory in assembly). You will also become familiar with how to use a Makefile to automate the compilation of your program.
1.2 Task
In this assignment, you will be managing a fictional class of students and ensuring that the administration of students goes smoothly.
You will write C functions to add a student, remove a student, update a student’s information, compare students, as well as sort the class of students. Your job is to make sure that certain rules are being followed and for some functions you will have to signal whether or not it completed successfully. See the Detailed Instructions section for more details on the specific requirements for each function.
You will write your C code in two files, my string.c and hw7.c. In my string.c, you will write your own implementations of common C library functions for working with strings: strlen(), strncmp(), and strncpy(). In hw7.c, you will implement the functionality as mentioned above regarding the class of students. Please see the Detailed Instructions below for more, well, detailed instructions.
Take a look at the sections on Makefiles and Testing and Example Output for more info on how to compile and test your program.
1.3 Criteria
Your C code must compile without errors or warnings, using the provided Makefile. Your array of structs should be populated correctly at the end of the program. Your helper functions in my string.c must all be implemented correctly, producing the same behavior for test cases as the equivalent library functions from string.h.
2 Detailed Instructions
2.1 “my string.c” functions
The first part of this homework is to implement three very common C string library functions:
• my strlen: compute the length of a null-terminated string
• my strncmp: compare two strings, up to at most n characters
• my strncpy: copy at most n characters from a source string to a target memory location
The caveat is that you must implement these functions using only pointer notation. That is, you cannot use array indexing notation, such as str[i] = ‘a’. This restriction only applies in the my string.c file. We recommend implementing these functions first so you are able to use these functions as you move on with the assignment.
You will notice that many of the arguments in the my string.c and hw7.c files are of type const char *. This is a pointer to a char that is constant. This means that you cannot edit any of the characters to which a const char * points to. If you attempt to do so, using something like *pointer = ’c’, you will get a compile error. If const does not precede a char * declaration, you can edit the characters to which it points to.
In order to understand the functionalities of these three library functions, you need to take a look at their man page (i.e. manual page). See the section on Man Pages for more info.
Some notes:
1. You are NOT allowed to use array notation in this file. All functions should be implemented using pointers only! Think about how arrays and pointers correlate with each other in C. Again, this restriction only applies to this file.
2. You are NOT allowed to use any of the standard C string libraries (e.g. #include <string.h>).
3. Although expressions passed in to this program have a min/max length, the string functions should not have a boundary on any arguments passed in.
4. For my strncmp, you do not need to return a specific number, as long as it follows the description in the man page.
2.2 hw7.c
• addStudent(const char *name, int age, double gpa, const char *id):
In this function, you will add a student struct with the given name, age, gpa, and id to the end of the class array. If the given name’s length (including the null terminator) is above MAX NAME SIZE, truncate the name to be MAX NAME SIZE. Be mindful of how strings are represented in C! If the given id’s length is smaller than MIN ID SIZE, of if the student with the given name already exists in the class array, or if adding the student would cause the number of students to exceed the maximum size of the class, do not create and add the student. Return SUCCESS when you are able to successfully create and add the student, otherwise return FAILURE.
• updateStudentName(struct student s, const char * name):
In this function, you will update a student so that their name is updated to the name parameter passed into this function. The student to be updated will be the student in the class array with the same name as s. If the updated name’s length (including the null terminator) is above MAX NAME SIZE, truncate the name to be MAX NAME SIZE. If you are able to successfully update the student’s name, return SUCCESS. If you are unable to find the student, return FAILURE.
• swapStudents(int index1, int index2):
In this function, you will swap the position of a student at index1 with the position of the student at index2. If the indices are invalid (such as a negative index or an index beyond the current size of the class) do no swap. On successful swap, return SUCCESS. Otherwise, return FAILURE;
• removeStudent(struct student s):
In this function, you will remove a student with the name in the passed in student struct. You must maintain array contiguity when removing. This means that there must be no gaps between students within the class array. On successful removal, return SUCCESS. If you cannot find the student with the given information, return FAILURE.
• compareStudentID(struct student s1, struct student s2);:
In this function, you will compare two students by using the last three characters of their IDs. If the string formed out of the last three characters of s1 is greater than the string formed out of the last three characters of s2, return a positive value. If it’s less than, return a negative value. If equivalent, return 0.
• sortStudentByID(void));:
In this function, you will sort the class array of students by using any sorting algorithm of your choice. The result should be in ascending order. The ordering of the sorted array is determined by compareStudentID.
2.3 hw7.h
Within this file, you be provided with the function prototypes, the definition of the student struct, as well as various macros that you can use in your implementation of the functions in hw7.c.
2.4 Makefiles and Testing
Since your program is connected to an autograder, it’s a little difficult to compile it by hand. To help you out with compiling and running tests, we’ve provided you with a Makefile.
Make is a common build tool for abstracting the complexity of working with compilers directly. In fact, the PDF you’re reading now was built with a Makefile! Makefiles let you define a set of desired targets, their prerequisites, and sets of directives to build those targets. In all of our C assignments (and also in production level C projects), a Makefile is used to compile C programs with a long list of compiler flags. We have already provided you a Makefile for this homework, and although you are not being tested on it, we highly recommend that you take a look at this file and understand the gcc commands and flags used to understand how to compile C programs. If you’re interested, you can also find more information regarding Makefiles here.
To test your code manually, compile your code using make and run the resulting object file with the commandline arguments of your choice.
Keep in mind that you should run all commands inside the Docker terminal. We highly recommend running the usual script as follows to immediately get a terminal:
./cs2110docker.sh -it
If you use your own Linux distribution/VM, make sure you have the check unit test framework installed. However, keep in mind that your code will be tested on Docker.
Below is an example of manually testing your code.
# Clean up all compiled output
$ make clean
# Recompile the hw7 executable
$ make hw7
# Run the hw7 executable
$ ./hw7
To run the autograder, see the Autograder section.
3 Useful Tips
3.1 Man Pages
The man command in Linux provides “an interface to the on-line reference manuals.” This is a great utility for any C and Linux developer for finding out more information about the available functions and libraries. In order to use this, you just need to pass in the function name to this command within a Linux (in our case Docker) terminal.
For instance, entering the following command will print the corresponding man page for the strlen function:
$ man strlen
Additionally, the man pages are accessible online at:
NOTE: You can ignore the subsections after the “RETURN VALUE” (such as ATTRIBUTES, etc) for this homework, however, pay close attention to function descriptions.
3.2 Debugging with GDB and printf
We highly recommend getting use to “printf debugging” in C early on.
Side Note: Get used to GDB early on as it will come in handy in any C program you will write for the rest of 2110, and even in the future!
When running GDB, if you get to a point where user input is needed, you can supply it just like you normally would. When an error happens, you can get a Java-esque stack trace using the backtrace(bt) command. For more info on basic GDB commands, search up “GDB Cheat Sheet.”
4 Checking Your Solution

Important Notes:
1. All non-compiling homework will receive a zero (with all the flags specified in the Makefile/Syllabus).
You must place any code elements you define (structs, macros, function declarations, etc.) in the C FILES. Usually placing those definitions in .h files would be good practice, but for this assignment you are not turning them in, and so the declarations would be lost when submitting.
To run the autograder locally (without GDB):
# To clean your working directory (use this instead of manually deleting .o files) $ make clean
# Compile all the required files
$ make tests
# Run the tester executable
$ ./tests
This will run all the test cases and print out a percentage, along with details of the failed test cases.
Other available commands:
• To run tests without gdb:
# Run all tests
$ make run-case
# Run a specific test
$ make run-case TEST=testCaseName
• To run tests with gdb:
# Run all tests in gdb $ make run-gdb
# Run a specific test in gdb
$ make run-gdb TEST=testCaseName
The output file will ONLY be graded on Gradescope.
Many test cases are randomly generated and your code should work every time we run the autograder on it, however, there’s no need to submit to Gradescope multiple times once you get the desired grade.
We reserve the right to update the autograder and the test case weights on Gradescope or the local checker as we see fit when grading your solution.
5 Deliverables
Please upload the following files to Gradescope:
1. my_string.c
2. hw7.c
Note: Please do not wait until the last minute to run/test your homework; history has proven that last minute turn-ins will result in long queue times for grading on Gradescope. You have been warned.
6 Appendix
6.1 Appendix D: Rules and Regulations
6.1.1 General Rules
1. Starting with the assembly homeworks, any code you write should be meaningfully commented for your benefit. You should comment your code in terms of the algorithm you are implementing; we all know what each line of code does.
3. Please read the assignment in its entirety before asking questions.
5. If you find any problems with the assignment, it would be greatly appreciated if you reported them to the TAs. Announcements will be posted if the assignment changes.
6.1.2 Submission Conventions
1. Unless otherwise noted, all files you submit for assignments should have your name somewhere near the top of the file as a comment.
3. Do not submit compiled files (.class files for Java code or .o files for C code). Only submit the files we ask for in the assignment.
4. Do not submit links to files. The autograder will not understand it, and we will not manually grade assignments submitted this way, as it is easy to change the files after the submission period ends.
6.1.3 Submission Guidelines
2. You are responsible for ensuring that you have turned in the correct files. After submitting, be sure to download your submission into a brand new folder and test that it works. What you turn in is what we grade; there are no excuses if you submit the wrong files. In addition, your assignment must be turned in via Canvas/Gradescope. Under no circumstances whatsoever will we accept any email submissions of assignments (Note: if you were granted an extension, you will still turn in the assignment over Canvas/Gradescope).
6.1.4 Syllabus Excerpt on Academic Misconduct
Academic misconduct is taken very seriously in this class. Quizzes, timed labs and the final examination are individual work.
Homework assignments are collaborative. In addition, many, if not all, homework assignments will be evaluated via demo or code review. During this evaluation, you will be expected to be able to explain every aspect of your submission. Homework assignments will also be programatically examined to find evidence of unauthorized collaboration.
You are expressly forbidden to supply a copy of your homework to another student via electronic means. This includes simply emailing it to them so they can look at it. If you supply an electronic copy of your homework to another student, and they are charged with copying, you will also be charged. This includes storing your code on any site which would allow other parties to obtain your code, including, but not limited to, public repositories (GitHub), Pastebin, etc. If you would like to use version control, use github.gatech.edu.
6.1.5 Is collaboration allowed?

Figure 1: Collaboration rules, explained colorfully


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