[SOLVED] COMP2017 / COMP9017 Tutorial 2 Addressable Memory and Standard Library Func

COMP2017 / COMP9017 Tutorial 2 Addressable Memory and Standard Library Functions
The Preprocessor and Function Prototypes
The preprocessor is part of the compilation pipeline that allows functions from separate translation units to be utilised in your source files and linked together. We are also able to define compile time constants and compile code based on conditions known at compile time. This functionality is exposed through the C preprocessor language and we will be focusing on using #define and #include to statements in our following C programs. Prior to compilation it will evaluate the preprocessor statements and replace the value the preprocessor symbol is defined as.
Although there exists a const modifier within the C language, you are able to define constants and macros to be evaluated at compilation using preprocessor directives. The #define directive allows us to express constants and macros to be used as part of our source code.

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#define PI 3.14
We can therefore use PI through out our program, during the preprocessor phase, wherever PI is encountered by the preprocessor, it will replace it with the value 3.14.
The #include statement allows you to bring in header files which will expose function prototypes your program for you to use. This preprocessor directive allows you to include other files (commonly header files) into your source code (similar to a copy and pasting).
A very common use with #include is to include stdio and stdlib header files. These header files provide access to the function prototypes and preprocessor constants such as printf, fopen, scanf and NULL.
#include
For local header files, we use the the double quotes around the file. #include local.h

COMP2017 / COMP9017 Addressable Memory and Standard Library Functions
Compilation with flags
You should make sure to compile your programs with the C11 standard and enable all compiler warnings with -Wall. You will be taught more useful compiler options in the future, in the mean time you can look up the clang man page to see other possible options.
$ clang -std=c11 -Wall -o
printf is used to print values to the standard output in C. This is a very useful function and you need to learn its parameters. The function prototype is:
int printf(const char* format, );
The first argument is the format string, and then takes zero or more arguments which are used to fill
in the placeholders within the format string.
In the simplest form, the format string simply echoes its value to standard output. The string is printed as given by the programmer. There are escape code/for characters that are bothersome to type or are used as part the C syntax, these are listed in the table below.
ESCAPE REPRESENTS
a Bell (alert)
b Backspace
Newline
r Carriage return t Tab space
ESCAPE REPRESENTS
Single quote
Double quote
\ Backslash
ooo Character in octal notation xhh Character in hex notation
Note: different operating systems use different characters to designate a new line. On Linux, the line feed character is used as the new line character. On Windows, the combination of a carriage return and line feed designate a new line. In C, if you specify
, then the compiler will substitute it with the appropriate characters for your operating system.
#include
int main(void) {
printf(int=%d float=%f string=%s
, 420, 3.141f, Hello from C); return 0;
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COMP2017 / COMP9017 Addressable Memory and Standard Library Functions The format string uses placeholders for printing C data types.
The placeholder always begins with % and has the following format: %[flags][width][.precision][length]specifier Here is a list of the most commonly used placeholders:
%d or %i %f
OUTPUT EXAMPLE
character a
signed integer 392
decimal floating point 392.65 NULL-terminated sequence of characters sample
unsigned integer 7235
unsigned hexadecimal integer 7fa
unsigned hexadecimal integer 7FA
pointer address 0x7fff6efe9ca8 literal percentage sign %%
The example program shown below outputs some records using more complicated placeholders:
#include
int main(void) {
printf(%-3s %-15s %-5s
, ID, Name, Score); const char* format = %03d %-15s %.2f
;
printf(format, 1, , 99.449);
printf(format, 2, , 99.999);
return 0; }
The %-15s tells printf to print all strings into a 15 character wide field and fill any leftover room with spaces. The gives it left alignment. %010d tells printf to pad the signed integer into a 10 character wide field and fill any leftover room with zeros. %.2f says to round the floating point value into 2 decimal places.
The output of the program is:
IDNameScore
00199.45
002100.00
Youcanreadthroughthedocumentationforprintfusing:$ man 3 printf
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COMP2017 / COMP9017 Addressable Memory and Standard Library Functions
To read and interpret string data from standard input, stdio.h provides the scanf function.
#include int main(void) {
int number;
if (scanf(%d, &number) != 1) {
puts(No number given);
return 1; }
printf(Your number is: %d
, number);
return 0; }
scanf uses the same placeholder format as the printf function. scanf requires you to pass a pointer to the variable as its parameters. This allows scanf to update the variable.
The & operator converts a variable to a pointer containing its address. Heres an example of using scanf to read formatted input:
#include int main(void) {
char buffer[20];
// Check all three inputs are given
if (scanf(%d %lf %19s, &x, &y, buffer) != 3) {
fprintf(stderr, Invalid input
);
return 1; }
printf(%d %f %s
, x, y, buffer);
return 0; }
The scanf function returns the number of input items successfully matched and assigned. This can be fewer than the number of arguments passed into it. It will return zero when it fails to read any input for any reason.
Note:bufferisanarrayandhastypechar[20],itautomaticallydecaysintoachar *thatcon- tains the address of the first element of the array. Its usage here is the same as writing &buffer[0].
When reading strings with scanf, you should provide a width specifier. This is because the buffer array we have declared is a fixed size. If a string longer than 20 characters was input (including the null terminator), scanf will write outside the bounds of array. This can potentially crash the program, overwrite the values of other variables or introduce a buffer overflow security vulnerability.
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COMP2017 / COMP9017 Addressable Memory and Standard Library Functions
Pre-tutorial Work Question 1: Shout
Write a C program that uppercases all letters inputted from the standard input. Characters that are not in the range [a-z] should pass through unchanged. You can use the toupper and getchar functions.
Sample input:
lorem ipsum
dolor sit amet
You can use toupper function as part of the ctype.h header, you can check out the toupper functionusingman 3 toupper.Alternativelyyoucanusetheasciitableasawayoftransforming the characters. As an extension, write a program that will transform all input to lower case.
Question 2: Travel and conversion
You are planning a road trip with your American friends. Given a kilometres per hour rate and the travel duration, you are curious how far you and your friends can travel.
Remembering that you need to communicate this distance to your American friends, you will also need to convert KM/h to M/h (miles per hour) as well as the distance travelled into miles. Round this down to
$ ./travel
What is your current km/h: 50
How many hours are you travelling for: 2.5
You will cover: 125.00 km (77.57 mi)
While travelling at 50 km/h (31.07 mph)
C strings and math library
C does not have a string type within its standard library. To represent a string in C, you will need to use a character array to store a sequence of characters, ending with a null character terminator. However, part of the C standard library is the string.h header that allows you to manipulate strings.
The standard library provides math functions that can be found within the math.h header file. You canfindthefunctionsbyusingthecommandman math.h.Usages:
#include
Typically when using math functions you will need to include link to the math library.
Sample output:
LOREM IPSUM
DOLOR SIT AMET
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COMP2017 / COMP9017 Addressable Memory and Standard Library Functions
gcc my_math_program.c -lm -o program
You will have your typical mathematical functions. However you will notice that some create a small distinction of the type they return by prepending an l or f to their name, denoting long or float respectively.
fma(x,y,z)
hypot(x,y)
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COMP2017 / COMP9017 Addressable Memory and Standard Library Functions
Question 3: C types and pointers
Answer the following questions without running any code.
You may check with the compiler after you have attempted these.
Suppose the variable int x has address 0x1000, and sizeof(int) is 4. Whatdoesprintf(%p %p
, &x, &x + 1)output?
Suppose the variable char y has address 0x1000. Whatdoesprintf(%p %p
, &y, &y + 1)output?
Suppose the first element of char z[100] has address 0x1000.
Whatdoesprintf(%p %p %td
, &z[1], z + 5, &z[12] &z[9])output? Whatdoesprintf(%p %p
, &z[3] 1, &z[20] 5)output?
Supposethefirstelementofdouble u[100]hasaddress0x1000,andsizeof(double) is 8
Whatdoesprintf(%p %p %td
, &u[1], u + 5, &u[12] &u[9])output? Whatdoesprintf(%p %p
, &u[3] 1, &u[20] 5)output?
What does printf(%c %d
, a + 1, z a) output?
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COMP2017 / COMP9017 Addressable Memory and Standard Library Functions
Question 4: Cricket
Write a C program that will store a batsmans name and the number of runs that they have scored and report the total runs and each score. If a batsman has not scored any runs, a Duck should be printed next to their name.
$ ./batsman
Enter Name and Score for batter 1: 40
Enter Name and Score for batter 2: 67
Enter Name and Score for batter 3: 123
Enter Name and Score for batter 4: 59
Enter Name and Score for batter 5: 21
Enter Name and Score for batter 6: 0
Enter Name and Score for batter 7:Dermott 0
Enter Name and Score for batter 8: Shaun Marsh 10
Enter Name and Score for batter 9: 78
Enter Name and Score for batter 10: 54
1. C. Bancroft: 40
2. M. Marsh: 67
3. J. Burns: 123
4. D. Warner: 59
5. T. Head: 21
6. W. Pucovski: Duck
7. B. McDermott: Duck
8. S. Marsh: 10
9. C. White: 78
10. U. Khawja: 54
You may assume the format is: and there at maxi-
mum 10 batsmen. The length of each first name and last name can be up to 100 characters.
As an extension you can attempt to solve this problem without assuming the maximum length of someones first and last name.
Question 5: Discuss Work
During the tutorial, discuss with your tutor your answers to question 3 and your implementation to question 4 (cricket scoring program).
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COMP2017 / COMP9017 Addressable Memory and Standard Library Functions
Tutorial Work
Question 6: Volume of a sphere
Write a C program that will calculate the volume of a sphere. The program must allow the user to input a radius.
In case you have forgotten how to calculate the the volume of a sphere, you can use the following formula:
V = 43 r 3
$ ./vsphere
Specify the radius of the sphere: 2
Volume is: 33.509335
You may use following definition of PI
const float PI = 3.1415;
After you have successfully written and tested your program, replace PI with M_PI from math.h. Check with your tutor about your compilation step if you run into trouble or refer to the C strings and math library of this tutorial.
Question 7: strlen
Implement your own strlen function. Note that the function definition for strlen uses const char* , this tells the compiler that this pointer can only be used to read. It is good practice to use only const pointers if you dont need to write to the memory referenced by the pointer.
#include
int my_strlen(const char* s) { //TODO
int main(void) {
printf(%d
, my_strlen());
printf(%d
, my_strlen(123));
printf(%d
, my_strlen(abc
));
printf(%d
, my_strlen(loremipsum
)); // should output 5 printf(%d
, my_strlen(lorem ipsum
)); // should output 12 return 0;
The strlen function is declared in the string.h header. You can double check your implemen-
tation by comparing it to the standard library function.
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// should output 0
// should output 3
// should output 4

COMP2017 / COMP9017 Addressable Memory and Standard Library Functions
Question 8: Finding a substring
Construct a function that will find the locate the starting index of a string within another. This function should return a negative value if the substring does not exist within the line.
int substring(const char* line, const char* substr) { //TODO
int main() {
printf(%d
, substring(racecar, car)); //4 printf(%d
, substring(telephone, one)); //6 printf(%d
, substring(monkey, cat)); //-1
Question 9: Run-length Encoding
A common compression method is to encode the run length of the same symbol. The method also shows up in puzzle games such as picross.
int encode_run(const char* sequence, unsigned len, char* buf, unsigned int buf_len) {
int main() {
char encoded_run[128];
const char* line_run = 1122333334423;
encode_run(line_run, 14, encoded_run, 128);
printf(%s
, encoded_run); // 225211 }
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COMP2017 / COMP9017 Addressable Memory and Standard Library Functions
Question 10: Run-length Tuples
Similar to the previous question, we want to encode the runs of a sequence. However, the twist with this function is that we want to encode what symbol the run relates to.
int encode_run(const char* sequence, unsigned len, char* buf, unsigned int buf_len) {
//TODO, Modify your existing run
int main() {
char encoded_run[128];
const char* line_run = 1122333334423;
encode_run(line_run, 14, encoded_run, 128);
// (1,2) (2,2) (3,5) (4,2) (2,1) (3,1)
Write a decoder function that will output the run from the tuples buffer.
int decode_run(const char* tuples, unsigned len) { //TODO, Modify your existing run
int main() {
char encoded_run[128];
const char* line_run = 1122333334423;
encode_run(line_run, 14, encoded_run, 128); //(1,2) (2,2) (3,5) (4,2) (2,1) (3,1)
decode_run(encoded_run, 128); //1122333334423 return 0;
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COMP2017 / COMP9017 Addressable Memory and Standard Library Functions
Question 11: Password generator
Using the random function rand and srand functions from stdlib.h, set the seed for the random function and generate a password for a user. Your program should utilise the ascii table and will need to include valid keyboard characters, symbols and integers.
The length of the password will be specified as a command line argument.
./pass_gen 8
You will need to use rand and srand, these functions are declared in the stdlib.h file. You can readthemanpagesofthestdlibheaderfilebyusingthecommandman stdlib.h.
Question 12: out
Your program should behave in a similar way to the Unix cat program. If no arguments are passed to your program, it should read from stdin and output the input. If arguments are passed to your program, it should treat each argument as a file and output the contents of each file in order.
You should use the following functions: fgets, fread, fopen and fprintf. $ echo hello | ./out
$ echo hello | ./out file1

$ ./cat file1 file2 file3



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