Coding exercise $($Language: C$)$

You tutor students part$-$time as part of your work$-$study program. Currently, the students are facing threads and memory management for the first time and they$$re having a hard time. To help them, you devised an exercise for them to practice with. One of the students submitted the following code, everything they added is encased to the base code supplied with $/*$Student$$s Code$*/$ Comment.

#include

#include

#include

int threads;

double sol$[100][100]$;

struct matrix$\{$ int data$[100][100]$; int size$1$; int size$2$; $\}$;

void $*$runner$($void $*$param$)\{$

$/*$Student$$s Code$*/$

struct matrix $*$matrices $=($struct matrix$*)$param;

int start$\_$row $=*(($int$*)$param$)$;

int end$\_$row $=$ start$\_$row $+1$;

for $($int i $=$ start$\_$row; i $<$ end$\_$row; i$++)\{$

for $($int j $=0$; j $<$ matrices$[1].$size$2$; j$++)\{$

sol$[$i$][$j$]=0$;

for $($int k $=0$; k $<$ matrices$[0].$size$2$; k$++)\{$

sol$[$i$][$j$]+=$ matrices$[0].$data$[$i$][$k$]*$ matrices$[1].$data$[$k$][$j$]$;

$\}$

$\}$

$\}$

$/*$Student$$s Code$*/$

pthread$\_$exit$(0)$;

$\}$

void matrixOperation$($int scalar, struct matrix X$,$ struct matrix Y$)\{$

$/*$Student$$s Code$*/$

pthread$\_$t tid$[$threads$]$;

int rows$\_$per$\_$thread $=$ X$.$size$1/$ threads;

int remaining$\_$rows $=$ X$.$size$1\%$ threads;

int thread$\_$args$[$threads$]$;

int start$\_$row $=0$;

for $($int i $=0$; i $<$ threads; i$++)\{$

thread$\_$args$[$i$]=$ start$\_$row;

int rows $=$ rows$\_$per$\_$thread $+($remaining$\_$rows $>0?1$ : $0)$;

remaining$\_$rows$--$;

start$\_$row $+=$ rows;

pthread$\_$create$($&tid$[$i$],$ NULL, runner, &thread$\_$args$[$i$])$;

$\}$

for $($int i $=0$; i $<$ threads; i$++)\{$

pthread$\_$join$($tid$[$i$],$ NULL$)$;

$\}$

$/*$Student$$s Code$*/$

$//$ Prints out the solution matrix

printf$("$Result $=$

$[")$;

for$($int i $=0$; i $<$ X$.$size$1$; i$++)\{$

printf$("[")$;

for$($int j $=0$; j $<$ X$.$size$2$; j$++)\{$

$($j$+1==$ X$.$size$2)?$ printf$("\%$f$",$ sol$[$i$][$j$])$ : printf$("\%$f$,",$ sol$[$i$][$j$])$;

$\}$

$($i$+1==$ X$.$size$1)?$ printf$("]")$ : printf$("],$

$")$;

$\}$

printf$("]$

$")$;

return;

$\}$

$/*$Student$$s Code$*/$

int main$()\{$

struct matrix X$,$ Y;

X$.$data$[0][0]=1$;

X$.$data$[0][1]=2$;

X$.$data$[1][0]=3$;

X$.$data$[1][1]=4$;

X$.$size$1=2$;

X$.$size$2=2$;

Y$.$data$[0][0]=5$;

Y$.$data$[0][1]=6$;

Y$.$data$[1][0]=7$;

Y$.$data$[1][1]=8$;

Y$.$size$1=2$;

Y$.$size$2=2$;

threads $=1$;

matrixOperation$(3,$ X$,$ Y$)$;

threads $=2$;

Y$.$data$[1][0]=12$;

matrixOperation$(2,$ X$,$ Y$)$;

Y$.$size$2=4$;

threads $=2$;

matrixOperation$(2,$ X$,$ Y$)$;

return $0$;

$\}$

$/*$Student$$s Code$*/$

Student$$s Result:

Result $=[[0\mathrm{.}000000,0\mathrm{.}000000],[0\mathrm{.}000000,0\mathrm{.}000000]]$

Result $=[[0\mathrm{.}000000,0\mathrm{.}000000],[0\mathrm{.}000000,0\mathrm{.}000000]]$

Result $=[[0\mathrm{.}000000,0\mathrm{.}000000],[0\mathrm{.}000000,0\mathrm{.}000000]]$

Expected Result:

Result $=[[18\mathrm{.}000000,24\mathrm{.}000000],[30\mathrm{.}000000,36\mathrm{.}000000]]$

Result $=[[12\mathrm{.}000000,16\mathrm{.}000000],[30\mathrm{.}000000,24\mathrm{.}000000]]$

ILLEGAL OPERATION

There are multiple errors within the code, how would you go about resolving those issues and explaining the changes made such that the student can improve? Was the approach efficient? $($Only use pThreads$)$