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ser334_unit2_exercise_sample.lyx
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ser334_unit2_exercise_sample.lyx
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#LyX 2.4 created this file. For more info see https://www.lyx.org/
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\begin_document
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\index Index
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\leftmargin 2.54cm
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\secnumdepth 3
\tocdepth 3
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\end_header
\begin_body
\begin_layout Standard
\noindent
Arizona State University
\begin_inset space \hfill{}
\end_inset
SER334:
Operating Systems & System Programming
\end_layout
\begin_layout Standard
\noindent
Lecturer Acuña (6),
UGTA Lisonbee (2)
\begin_inset space \hfill{}
\end_inset
Revised 9/3/2024
\end_layout
\begin_layout Standard
\noindent
\begin_inset CommandInset line
LatexCommand rule
offset "0.5ex"
width "100col%"
height "1pt"
\end_inset
\end_layout
\begin_layout Standard
\size huge
Unit 2 Sample Problems - C Programming II
\end_layout
\begin_layout Standard
\begin_inset VSpace bigskip
\end_inset
\end_layout
\begin_layout Standard
In this sample problem set,
we will practice concepts of the C programming language.
\end_layout
\begin_layout Itemize
Length:
60 minutes with discussion.
\end_layout
\begin_layout Itemize
Questions:
Q1-Q3,
Q5-Q7.
(optional:
Q4,
Q8)
\end_layout
\begin_layout Standard
\begin_inset Formula $\;$
\end_inset
\end_layout
\begin_layout Standard
\series bold
\size larger
Memory Allocation
\end_layout
\begin_layout Enumerate
[Acuña] Consider the following snippet of code.
[4 points total]
\end_layout
\begin_deeper
\begin_layout Standard
\begin_inset listings
lstparams "language=C"
inline false
status open
\begin_layout Plain Layout
struct point_2d {
\end_layout
\begin_layout Plain Layout
int x;
\end_layout
\begin_layout Plain Layout
int y;
\end_layout
\begin_layout Plain Layout
Color col;
\end_layout
\begin_layout Plain Layout
};
\end_layout
\begin_layout Plain Layout
\end_layout
\begin_layout Plain Layout
void main() {
\end_layout
\begin_layout Plain Layout
point_2d* data[5];
\end_layout
\begin_layout Plain Layout
for(int i = 0;
i < 5;
i++) {
\end_layout
\begin_layout Plain Layout
point_2d tmp;
\end_layout
\begin_layout Plain Layout
tmp.x = i;
\end_layout
\begin_layout Plain Layout
tmp.y = i * i;
\end_layout
\begin_layout Plain Layout
data[i] = &tmp;
\end_layout
\begin_layout Plain Layout
}
\end_layout
\begin_layout Plain Layout
for(int i = 0;
i < 5;
i++)
\end_layout
\begin_layout Plain Layout
printf("Point #%d:
%d,
%d",
i,
data[i]->x,
data[i]->y);
\end_layout
\begin_layout Plain Layout
}
\end_layout
\end_inset
\end_layout
\begin_layout Enumerate
What will be the output?
\series bold
Trace this code manually,
do not run it.
\end_layout
\begin_deeper
\begin_layout Standard
\begin_inset Branch blank
inverted 0
status collapsed
\begin_layout Standard
\begin_inset VSpace 4cm
\end_inset
\end_layout
\end_inset
\end_layout
\begin_layout Standard
\begin_inset Branch soln
inverted 0
status collapsed
\begin_layout Standard
Ans:
[Acuña]
\end_layout
\begin_layout Standard
"Point #0:
4,
16",
"Point #1:
4,
16",
"Point #2:
4,
16",
"Point #3:
4,
16",
and "Point #4:
4,
16".
\end_layout
\begin_layout Standard
\begin_inset VSpace 2cm
\end_inset
\end_layout
\end_inset
\end_layout
\end_deeper
\begin_layout Enumerate
Why does the program give that output?
Explain in terms of memory and pointer usage.
\end_layout
\begin_deeper
\begin_layout Standard
\begin_inset Branch blank
inverted 0
status collapsed
\begin_layout Standard
\begin_inset VSpace 6cm
\end_inset
\end_layout
\end_inset
\end_layout
\begin_layout Standard
\begin_inset Branch soln
inverted 0
status collapsed
\begin_layout Standard
Ans:
[Acuña]
\end_layout
\begin_layout Standard
Each iteration of the loop is getting the address of the same piece of memory.
Since the last thing assigned to that place is the 4/16 point,
then the display will show that value.
\end_layout
\begin_layout Standard
\begin_inset VSpace 4cm
\end_inset
\end_layout
\end_inset
\end_layout
\end_deeper
\end_deeper
\begin_layout Enumerate
[Acuña] Consider the following (incorrect) function which removes the head node in a globally defined list called
\emph on
my_list
\emph default
.
The struct
\emph on
grade_node
\emph default
is used to represent a node containing grade information in a linked list of grades.
\end_layout
\begin_deeper
\begin_layout Standard
\begin_inset listings
lstparams "language=C"
inline false
status open
\begin_layout Plain Layout
struct grade_node {
\end_layout
\begin_layout Plain Layout
int value;
\end_layout
\begin_layout Plain Layout
char assignment[255];
\end_layout
\begin_layout Plain Layout
struct grade_node* next;
\end_layout
\begin_layout Plain Layout
};
\end_layout
\begin_layout Plain Layout
\end_layout
\begin_layout Plain Layout
struct grade_node* my_list = ...
\end_layout
\begin_layout Plain Layout
\end_layout
\begin_layout Plain Layout
void remove_node() {
\end_layout
\begin_layout Plain Layout
free(my_list);
\end_layout
\begin_layout Plain Layout
if(my_list != null)
\end_layout
\begin_layout Plain Layout
my_list = my_list->next;
\end_layout
\begin_layout Plain Layout
}
\end_layout
\end_inset
\end_layout
\begin_layout Enumerate
What is the syntax error in remove_node?
\end_layout
\begin_deeper
\begin_layout Standard
\begin_inset Branch blank
inverted 0
status collapsed
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\begin_inset VSpace 3cm
\end_inset
\end_layout
\end_inset
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\begin_layout Standard
\begin_inset Branch soln
inverted 0
status collapsed
\begin_layout Standard
\series bold
Ans:
[Karaliova]
\end_layout
\begin_layout Standard
NULL in C is defined in all caps (because it is a macro),
using 'null' will trigger a compiler error.
\begin_inset VSpace 2cm
\end_inset
\end_layout
\end_inset
\end_layout
\end_deeper
\begin_layout Enumerate
What is the logical error in remove_node?
\end_layout
\begin_deeper
\begin_layout Standard
\begin_inset Branch blank
inverted 0
status collapsed
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\begin_inset VSpace 3cm
\end_inset
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\begin_layout Standard
\begin_inset Branch soln
inverted 0
status collapsed
\begin_layout Standard
\series bold
Ans:
[Karaliova]
\end_layout
\begin_layout Standard
Using free(my_list) prevents us from being able to access the pointer to the next element for the head node of the list.
In other words,
the list is no longer accessible.
Instead we should store the pointer to the current head of the list in a temp node first.
Then,
we need to set head's next node to be new lists's head.
Temp node can now be removed:
\end_layout
\begin_layout Standard
\begin_inset listings
lstparams "language=C"
inline false
status open
\begin_layout Plain Layout
void remove_node() {
\end_layout
\begin_layout Plain Layout
if(my_list != NULL) {
\end_layout
\begin_layout Plain Layout
grade_node* tmp = my_list;
\end_layout
\begin_layout Plain Layout
\end_layout
\begin_layout Plain Layout
my_list = my_list->next;
\end_layout
\begin_layout Plain Layout
free(tmp);
\end_layout
\begin_layout Plain Layout
tmp = NULL;
\end_layout
\begin_layout Plain Layout
}
\end_layout
\begin_layout Plain Layout
}
\end_layout
\end_inset
\end_layout
\end_inset
\end_layout
\end_deeper
\begin_layout Standard
\series bold
\size larger
Defining New Types
\end_layout
\end_deeper
\begin_layout Enumerate
[Acuña] Consider the problem of padding the following structure,
and answer the three questions below.
Assume that you are compiling on a system with a 32-bit architecture.
[4 points total]
\end_layout
\begin_deeper
\begin_layout Standard
\begin_inset listings
lstparams "language=C"
inline false
status open
\begin_layout Plain Layout
struct bmp_header {
\end_layout
\begin_layout Plain Layout
char creator_name[254];
\end_layout
\begin_layout Plain Layout
int width;
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int height;
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char signature_rgb[2];
\end_layout
\begin_layout Plain Layout
int offset_pixels;
\end_layout
\begin_layout Plain Layout
};
\end_layout
\end_inset
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\begin_layout Enumerate
What is the size of this struct as defined?
\end_layout
\begin_deeper
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\begin_inset Branch blank
inverted 0
status open
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\begin_inset VSpace 1cm
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inverted 0
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\begin_layout Standard
\series bold
Ans:
[Karaliova]
\end_layout
\begin_layout Standard
Total size of structure = ( 254 + 2 ) + 4 + 4 + (2 + 2) + 4 = 272 bytes
\end_layout
\begin_layout Standard
\begin_inset Tabular
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<column alignment="center" valignment="top">
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254 bytes
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4 bytes
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4 bytes
\end_layout
\end_inset
</cell>
<cell alignment="center" valignment="top" topline="true" bottomline="true" leftline="true" rightline="true" usebox="none">
\begin_inset Text
\begin_layout Plain Layout
\size scriptsize
2 bytes
\end_layout
\end_inset
</cell>
<cell alignment="center" valignment="top" topline="true" bottomline="true" leftline="true" rightline="true" usebox="none">
\begin_inset Text
\begin_layout Plain Layout
\series bold
\size scriptsize
2 bytes
\end_layout
\end_inset
</cell>
<cell alignment="center" valignment="top" topline="true" bottomline="true" leftline="true" rightline="true" usebox="none">
\begin_inset Text
\begin_layout Plain Layout
\size scriptsize
4 bytes
\end_layout
\end_inset
</cell>
</row>
</lyxtabular>
\end_inset
\end_layout
\begin_layout Standard
\begin_inset VSpace 1cm
\end_inset
\end_layout
\end_inset
\end_layout
\end_deeper
\begin_layout Enumerate
How much space would be wasted with word length padding?
\end_layout
\begin_deeper
\begin_layout Standard
\begin_inset Branch blank
inverted 0
status open
\begin_layout Standard
\begin_inset VSpace 1cm
\end_inset
\end_layout
\end_inset
\end_layout
\begin_layout Standard
\begin_inset Branch soln
inverted 0
status collapsed
\begin_layout Standard
\series bold
Ans:
[Karaliova]
\end_layout
\begin_layout Standard
Total size of padding = 2 bytes + 2 bytes = 4 bytes
\begin_inset VSpace 2cm
\end_inset
\end_layout
\end_inset
\end_layout
\end_deeper
\end_deeper
\begin_layout Enumerate
[Acuña] One of the issues with using unions is that it can be unclear which element in the union is the one currently being used.
Suggest a mechanism to indicate which element is active.