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General: The purpose of this project is to get some experience with arrays, pointers and memory

management. Mastery of these concepts is critical to C programming. Unless you really know what

you’re doing with pointers and memory allocation, you are a danger to society (well, figuratively

speaking, we hope). When I wrote this assignment, I presumed that you understood the mathematical

construct of a Matrix, and the calculation necessary to multiply two matrices together.

Your Mission: Edit the file “Project2.cpp” and implement the functions multiplyMatrices,

transposeMatrix, and multiplyMatricesPtr.

Stage 1, Matrix Multiplication: Recall the mathematical definition of a matrix product. Given an

MxN matrix A (M rows and N columns), and an NxK matrix B, calculate the MxK result matrix C as

follows:

Each element Cij = Ai0B0j + Ai1B1j + Ai2B2j + … + Ai(n-1)B(n-1)j

Every element of C must be computed this way. So, we’ll need two nested while loops, one for i

(which goes from 0 to M, the number of rows in A), and one loop for j, (which goes from 0 to K the

number of columns in B). Nested at the innermost level will be yet another while loop (I call mine

the “k-loop”) which goes from 0 to N and calculates the sum for each Cij.

Your function should have these three loops, one nested inside the other. You must, however,

explicitly code the function to use row-major ordering for the matrix storage. That means that Aij is

stored in the location a[i * a_cols + j] where a_cols is the variable holding the number of columns in

A (N in the discussion above). The matrices B and C are similarly stored in the arrays b[] and c[]

respectively. For your convenience, the code you are given for multiplyMatrices defines the variables

a_rows, a_cols, b_rows, b_cols, c_rows and c_cols (well, some are parameters, others are defined as

local variables, some may not be there). You may not need to use all these variables. If you decide

not to use them, please delete the variable definitions.

Stage 2, Matrix Multiplication with Dynamic Matrices: Implement function multiplyMatricesPtr

that works with dynamic matrices. Each dynamic matrix consists of an array of pointers such that

each element in the array points to one row of the matrix. (See class materials for details.) Both the

array of points, as well as each row, are dynamically allocated. As the result of multiplyMatricesPtr

function, you should return a new dynamic matrix (of appropriate size) that contains the result of

multiplication. We will “free” your matrix, so if you do not allocate appropriate size (or if you

change the format of the matrix), the program will crash.

Stage 3, Matrix Transpose: Implement function transposeMatrixPtr. Same as in the previous stage,

the resulting matrix should be dynamically allocated. The format of the matrix is described in the

previous stage. We will “free” your matrix, so if you do not allocate in the format that we expect the

program will crash.

Testing

You may develop your code any way you like, but the final testing should be on kamek (not

luigi, or any of the other 64-bit servers), using our Makefile.

FAQ

Q1: What does running ‘make’ do?

A: make, without any arguments, generates your executable called proj2. make test

generates proj2 and then executes it.

Q2: What does make clean do?

A: make clean removes all your object code and executable files (proj2), so that you can

start your compilation and linking afresh.

Q3: My code is working on my machine, but not on kamek.

A: Remove the –std=c++11 flag from the Makefile wherever it appears.

Try running ‘make clean’ to remove all your generated files before running ‘make’

again.

Q4: I am seeing a warning about files being time-stamped in the future.

A: Some of the machines have a whacky clock. kamek seems to be OK, so run your code

there.

Q5:In multiplyMatricesPtr, when we allocate the matrix C=A*B, should we perform error

checking to see if malloc succeeded? If it fails, should we abort the program? Or can we just

assume malloc will succeed?

A: Assume that malloc will succeed.

Q6: Can we get more test cases for stage 2?

A: Not from the instructors, no. You must make your own, and you are welcome to share them

on Piazza.

Q7: My gcc/g++ is not working on kamek with the Makefile.

A: In order to run the provided Makefile on the LRC servers, please log on to kamek and enter

the following command:

module initadd gcc

Then log out of the server and log back in.

This will permanently update gcc and g++ on your account on the server so that they will be

compatible with our Makefile.

CHECKLIST – Did you remember to:

¨ Re-read the requirements after you finished your program to ensure that you meet all

of them?

¨ Make sure that your program does not need modifications of main.cpp to work?

¨ Make sure that your program passes all our testcases?

¨ Seal all memory leaks?

¨ Make up your own testcases?

¨ Upload your solution to Canvas (Project2.cpp)? If you have multiple files, you should

zip them up into a file called Project2_

Please consult with us if you have multiple files.

¨ Download your uploaded solution into a fresh directory and re-run all testcases?