Week 08 Laboratory Exercises

Objectives

  • working with structs and pointers
  • introducing linked lists
  • using memory allocation

Preparation

Before the lab you should re-read the relevant lecture slides and their accompanying examples.

Exercise — in pairs:
Pet Statistics

In this exercise, you will read some pet information from standard input and relay it in a human readable format.

Download pet_stats.c here, or copy it to your CSE account using the following command:

cp -n /web/cs1511/21T1/activities/pet_stats/pet_stats.c .

New! You can view a diagram explaining the code here
pet_stats.c already contains a struct for a pet and a main function. You cannot change either of these and can only make changes to the functions: setup_pet() and print_pet().

Your task in this exercise is first to complete the function setup_pet() so that it:

  • Stores the first input string in the name field
  • Stores the second input string in the type field
  • Converts the third input string into an int and stores it in the age field
  • Converts the fourth input string into an int and stores it in the weight field

Hint: You may need the strtol() function to convert a string into an int.
You can assume each string contains at most 50 characters.

You will then need to complete the function print_pet() so that it writes out a single line of text describing the pet, like: "Mr_Snuffle-uffle-kins is a cat who is 4 years old and weighs 6kg\n"

When you have completed the functions setup_pet() and print_pet() this is how pet_stats.c should behave:

dcc -o pet_stats pet_stats.c
./pet_stats Mr_Snuffle-uffle-kins cat 4 6
Mr_Snuffle-uffle-kins is a cat who is 4 years old and weighs 6kg
./pet_stats 007  British_Short-hair 35 78
007 is a British_Short-hair who is 35 years old and weighs 78kg
You can run an automated code style checker using the following command:
1511 style pet_stats.c

When you think your program is working, you can use autotest to run some simple automated tests:

1511 autotest pet_stats

When you are finished working on this exercise, you and your lab partner must both submit your work by running give:

give cs1511 lab08_pet_stats pet_stats.c

Note, even though this is a pair exercise, you both must run give from your own account before Monday 12 April 20:00 to obtain the marks for this lab exercise.

Exercise — in pairs:
Print out the elements of a Linked List

Download list_print.c here, or copy it to your CSE account using the following command:

cp -n /web/cs1511/21T1/activities/list_print/list_print.c .

Your task is to add code to this function in list_print.c:

// print a linked list in this format:
// 17 -> 34 -> 51 -> 68 -> X
void print(struct node *head) {

    // PUT YOUR CODE HERE
}
print is given one argument, head, which is the pointer to the first node in a linked list.

Add code to print so that it prints the elements in the list

For example if the linked list contains these 8 elements:

1, 7, 8, 9, 13, 19, 21, 42

print should print 1 -> 7 -> 8 -> 9 -> 13 -> 19 -> 21 -> 42 -> X

Testing

list_print.c also contains a main function which allows you to test your print function.

This main function:

  • converts the command-line arguments to a linked list
  • assigns a pointer to the first node in the linked list to head
  • calls list_print(head)

Do not change this main function. If you want to change it, you have misread the question.

Your list_print function will be called directly in marking. The main function is only to let you test your list_print function

Here is how you use main function allows you to test list_print:

dcc list_print.c -o list_print
./list_print 1 2 4 8 16 32 64 128 256
1 -> 2 -> 4 -> 8 -> 16 -> 32 -> 64 -> 128 -> 256 -> X
./list_print 2 4 6 5 8 9
2 -> 4 -> 6 -> 5 -> 8 -> 9 -> X
./list_print 42 4
42 -> 4 -> X
./list_print 43
43 -> X
./list_print
X

Assumptions/Restrictions/Clarifications.

print should not change the linked list it is given. Your function should not change the next or data fields of list nodes.

print should not use arrays.

print should not call malloc.

print should not call scanf (or getchar or fgets).

Do not change the supplied main function. It will not be tested or marked.

You can run an automated code style checker using the following command:
1511 style list_print.c

When you think your program is working, you can use autotest to run some simple automated tests:

1511 autotest list_print

When you are finished working on this exercise, you and your lab partner must both submit your work by running give:

give cs1511 lab08_list_print list_print.c

Note, even though this is a pair exercise, you both must run give from your own account before Monday 12 April 20:00 to obtain the marks for this lab exercise.

Exercise — in pairs:
Insert an element at the head of a Linked List

Download list_insert_head.c here, or copy it to your CSE account using the following command:

cp -n /web/cs1511/21T1/activities/list_insert_head/list_insert_head.c .

Your task is to add code to this function in list_insert_head.c:

// Insert a new node containing value at the start of the linked list.
// The head of the new list is returned.
struct node *insert_head(int value, struct node *head) {

    // PUT YOUR CODE HERE (change the next line!)
    return NULL;

}
insert_head is given two arguments, value and head. value is an int. head is the pointer to the first node in a linked list.

Add code to insert_head so that it creates a new list node (using malloc) containing value and places it at the start of the list.

insert_head should return a pointer to the new list.

For example if value is 12 and the linked list contains these 3 elements:

16, 7, 8

insert_head should return a pointer to a list with these elements:

12, 16, 7, 8

Testing

list_insert_head.c also contains a main function which allows you to test your insert_head function.

This main function:

  • converts the command-line arguments to a linked list
  • assigns a pointer to the first node in the linked list to head
  • reads a single integer from standard input and assigns it to value
  • calls insert_head(value, head)
  • prints the result.

Do not change this main function. If you want to change it, you have misread the question.

Your insert_head function will be called directly in marking. The main function is only to let you test your insert_head function

dcc list_insert_head.c -o list_insert_head
./list_insert_head 16 7 8
12
[12, 16, 7, 8]
./list_insert_head 16
42
[42, 16]
./list_insert_head
2
[2]

Assumptions/Restrictions/Clarifications.

insert_head should not use arrays.

insert_head should not call scanf (or getchar or fgets).

insert_head should not print anything. It should not call printf.

Do not change the supplied main function. It will not be tested or marked.

You can run an automated code style checker using the following command:
1511 style list_insert_head.c

When you think your program is working, you can use autotest to run some simple automated tests:

1511 autotest list_insert_head

When you are finished working on this exercise, you and your lab partner must both submit your work by running give:

give cs1511 lab08_list_insert_head list_insert_head.c

Note, even though this is a pair exercise, you both must run give from your own account before Monday 12 April 20:00 to obtain the marks for this lab exercise.

Exercise — in pairs:
Find an element in a Linked List

Download list_contains.c here, or copy it to your CSE account using the following command:

cp -n /web/cs1511/21T1/activities/list_contains/list_contains.c .

Your task is to add code to this function in list_contains.c:

// Return 1 if value occurs in linked list, 0 otherwise
int contains(int value, struct node *head) {

    // PUT YOUR CODE HERE (change the next line!)
    return 42;

}
contains is given two arguments, an int value and head, which is the pointer to the first node in a linked list.

Add code to contains so that its returns 1 if value occurs in the linked and otherwise it returns 0.

For example if the linked list contains these 8 elements:

1, 7, 8, 9, 13, 19, 21, 42

and contains is called with value of 9,

contains should return 1.

Testing

list_contains.c also contains a main function which allows you to test your contains function.

This main function:

  • converts the command-line arguments to a linked list
  • assigns a pointer to the first node in the linked list to head
  • reads a single integer from standard input and assigns it to value
  • calls list_contains(value, head)
  • prints the result.

Do not change this main function. If you want to change it, you have misread the question.

Your list_contains function will be called directly in marking. The main function is only to let you test your list_contains function

Here is how you use main function allows you to test list_contains:

dcc list_contains.c -o list_contains
./list_contains 1 2 3 4
3
1
./list_contains 1 2 3 4
42
0
./list_contains 15 17 17 18
17
1
./list_contains 15 17 17 18
21
0
./list_contains
42
0

Assumptions/Restrictions/Clarifications.

contains should return a single integer.

contains should not change the linked list it is given. Your function should not change the next or data fields of list nodes.

contains should not use arrays.

contains should not call malloc.

contains should not call scanf (or getchar or fgets).

contains should not print anything. It should not call printf.

Do not change the supplied main function. It will not be tested or marked.

You can run an automated code style checker using the following command:
1511 style list_contains.c

When you think your program is working, you can use autotest to run some simple automated tests:

1511 autotest list_contains

When you are finished working on this exercise, you and your lab partner must both submit your work by running give:

give cs1511 lab08_list_contains list_contains.c

Note, even though this is a pair exercise, you both must run give from your own account before Monday 12 April 20:00 to obtain the marks for this lab exercise.

Challenge Exercise — individual:
Insert into the nth position in a Linked List

Download list_insert_nth.c here, or copy it to your CSE account using the following command:

cp -n /web/cs1511/21T1/activities/list_insert_nth/list_insert_nth.c .

Your task is to add code to this function in list_insert_nth.c:

// Insert a new node containing value at position n of the linked list.
// if n == 0, node is inserted at start of list
// if n >= length of list, node is appended at end of list
// The head of the new list is returned.
struct node *insert_nth(int n, int value, struct node *head) {

    // PUT YOUR CODE HERE (change the next line!)
    return NULL;

}
insert_nth is given three arguments, n, value and head. n is an int. value is an int. head is the pointer to the first node in a linked list.

Add code to insert_nth so that it creates a new list node (using malloc) containing value and places it before position n of the list.

The elements are counted in the same manner as array elements (zero-based), so the first element in the list is regarded as at position 0, the second element position 1 and so on.

If there are less than n elements in the list, the new list node should be appended to the end of the list.

insert_nth should return a pointer to the new list.

For example if n is 1 and value is 12 and the linked list contains these 3 elements:

16, 7, 8

insert_nth should return a pointer to a list with these elements:

16, 12, 7, 8

Testing

list_insert_nth.c also contains a main function which allows you to test your insert_nth function.

This main function:

  • converts the command-line arguments to a linked list
  • assigns a pointer to the first node in the linked list to head
  • reads an integer from standard input and assigns it to n
  • reads a second integer from standard input and assigns it to value
  • calls insert_nth(n, value, head)
  • prints the result.

Do not change this main function. If you want to change it, you have misread the question.

Your insert_nth function will be called directly in marking. The main function is only to let you test your insert_nth function

dcc list_insert_nth.c -o list_insert_nth
./list_insert_nth 16 7 8
0
12
[12, 16, 7, 8]
./list_insert_nth 16 7 8
1
12
[16, 12, 7, 8]
./list_insert_nth 16 7 8
2
12
[16, 7, 12, 8]
./list_insert_nth 16 7 8
3
12
[16, 7, 8, 12]
./list_insert_nth 16 7 8
42
12
[16, 7, 8, 12]
./list_insert_nth 42
0
16
[16, 42]
./list_insert_nth
0
2
[2]
./list_insert_nth
10
2
[2]

Assumptions/Restrictions/Clarifications.

insert_nth should not use arrays.

insert_nth should not call scanf (or getchar or fgets).

insert_nth should not print anything. It should not call printf.

Do not change the supplied main function. It will not be tested or marked.

You can run an automated code style checker using the following command:
1511 style list_insert_nth.c

When you think your program is working, you can use autotest to run some simple automated tests:

1511 autotest list_insert_nth

When you are finished working on this exercise, you must submit your work by running give:

give cs1511 lab08_list_insert_nth list_insert_nth.c

You must run give before Monday 12 April 20:00 to obtain the marks for this lab exercise. Note that this is an individual exercise, the work you submit with give must be entirely your own.

Challenge Exercise — individual:
Reverse a Linked List

Download list_reverse.c here, or copy it to your CSE account using the following command:

cp -n /web/cs1511/21T1/activities/list_reverse/list_reverse.c .

Your task is to add code to this function in list_reverse.c:

//
// Place the list pointed to by head into reverse order.
// The head of the list is returned.
//
struct node *reverse(struct node *head) {

    // PUT YOUR CODE HERE (change the next line!)
    return NULL;

}
Note list_reverse.c uses the following familiar data type:
struct node {
    struct node *next;
    int          data;
};
list_reverse is given one argument, head, which is the pointer to the first node in the linked list.

Add code to reverse which rearranges the list to be in reverse order.

reverse should return a pointer to the new list.

reverse must rearrange the list by changing the next fields of nodes.

reverse must not change the data fields of nodes.

For example if the linked list contains these 8 elements:

16, 7, 8, 12, 13, 19, 21, 12

reverse should return a pointer to a list with these elements:

12, 21, 19, 13, 12, 8, 7, 16

Testing

list_reverse.c also contains a main function which allows you to test your list_reverse function.

This main function:

  • converts the command-line arguments to a linked list
  • assigns a pointer to the first node in the linked list to head
  • calls reverse(head)
  • prints the result.

Do not change this main function. If you want to change it, you have misread the question.

Your list_reverse function will be called directly in marking. The main function is only to let you test your list_reverse function

cp -n /web/cs1511/21T1/activities/list_reverse/list_reverse.c .
dcc list_reverse.c -o list_reverse
./list_reverse 16 7 8 12 13 19 21 12
[12, 21, 19, 13, 12, 8, 7, 16]
./list_reverse 2 4 6 2 4 6
[6, 4, 2, 6, 4, 2]
./list_reverse 42
[42]
./list_reverse
[]

Assumptions/Restrictions/Clarifications.

list_reverse should not change the data fields of list nodes.

list_reverse should not use arrays.

list_reverse should not call malloc.

list_reverse should not call scanf (or getchar or fgets).

list_reverse should not print anything. It should not call printf.

Do not change the supplied main function. It will not be tested or marked.

You can run an automated code style checker using the following command:
1511 style list_reverse.c

When you think your program is working, you can use autotest to run some simple automated tests:

1511 autotest list_reverse

When you are finished working on this exercise, you must submit your work by running give:

give cs1511 lab08_list_reverse list_reverse.c

You must run give before Monday 12 April 20:00 to obtain the marks for this lab exercise. Note that this is an individual exercise, the work you submit with give must be entirely your own.

Submission

When you are finished each exercises make sure you submit your work by running give.

You can run give multiple times. Only your last submission will be marked.

Don't submit any exercises you haven't attempted.

If you are working at home, you may find it more convenient to upload your work via give's web interface.

Remember you have until Week 9 Monday 20:00 to submit your work.

You cannot obtain marks by e-mailing your code to tutors or lecturers.

You check the files you have submitted here.

Automarking will be run by the lecturer several days after the submission deadline, using test cases different to those autotest runs for you. (Hint: do your own testing as well as running autotest.)

After automarking is run by the lecturer you can view your results here. The resulting mark will also be available via give's web interface.

Lab Marks

When all components of a lab are automarked you should be able to view the the marks via give's web interface or by running this command on a CSE machine:

1511 classrun -sturec