Systems Programming (XMUT)
Assignment 1: C programming

  • Due 6 October 7 pm

To Submit:

  • part1.txt
  • editor.c

ALERT! Do not rename these files.

This assignment is divided into 2 parts.

  • In Part I, you will be asked to answer questions about Weeks 1--3 topics, submitted in a plain text file named part1.txt
  • In Part II, you will be asked to implement C functions, submitted in a file named editor.c

Part 1: Concepts (30%)

right This part will test your conceptual knowledge of C fundamentals, including operators, arrays, and strings. Your answers must be submitted in a plain text file named part1.txt.

Core [20 Marks]

  1. [4 Marks] Are the following valid or invalid C identifiers?
    1. while
    2. record_100
    3. $record
    4. integer-counter
  2. [8 Marks] Suppose a, b and c are integer variables that have been assigned the values a = 7, b = 3 and c = 5. What is the value of each of the following expressions?
    1. a + b + c
    2. a / b
    3. a % b
    4. a * b % c
  3. [8 Marks] Suppose cl, c2 and c3 are character-type variables that have been assigned the characters 'D', '4' and '?', respectively. Based on the ASCII character set, what is the numerical value of each of the following expressions?
    1. c1 + c2 + c3
    2. c1 - 'A'
    3. 3 * c2
    4. '3' * c2

Completion [7 Marks]

  1. [1 Marks] Given the following C code snippet, what is the type of the expression c+i+l? Briefly explain your answer. 
       char c;
   int i;
   long l;
  2. [2 Marks] Given the following C code snippet, what is the value assigned to k in the 2nd line? Briefly explain your answer. 
       int i = 8, j = 6, k; 
   k = (j > 5) ? i : j;
  3. [2 Marks] What is the problem (if any) in the following C statement? 
       int rem = 10.0 / 4 % 2;
  4. [2 Marks] Rewrite the following code, using a for-loop, to produce the same output. 
       int main (void) 
   {
       int j = 5;
       while(j >= 0) 
           printf("%d ", --j);
       return 0;
   }

Challenge [3 Marks]

  1. [1 Marks] What is the value of i, j, and k after the last statement in the following C code snippet? Explain your answer by showing step-by-step solution. 
       int i = 5, j = 10, k = 1;
   (k += 3*--i) - j++;
  2. [2 Marks] What is the output of the following code fragment? Explain your answer. 
       char string[] = "One\0Two\0Three";
   printf("%d", strlen(string));

Part 2: Practical Programming (70%)

This part will test your application of the conceptual knowledge of C fundamentals to solve practical programming tasks. You may only use the Standard C Library to perform the tasks in this part. You must implement the functions in a file named editor.c.

The programming tasks involve the implementation of several basic text editor operations: insert, delete, replace, etc. An important component of a text editor is the editing buffer which can be viewed as a one-dimensional array of characters.

The functions you will be implementing deal with manipulating the contents of the editing buffer:
  1. for Core (Tasks 1 and 2), you will implement editor_insert_char and editor_delete_char;
  2. for Completion (Task 3), you will implement editor_replace_str.

Sample code showing an example of how you can test your code is provided under the files directory in the archive that contains this file.

Commenting

You should provide appropriate comments to make your source code readable. If your code does not work and there are no comments, you may lose all marks.

Coding Style

You should follow a consistent coding style when writing your source code. Coding style (aka coding standard) refers to the use of appropriate indentation, proper placement of braces, proper formatting of control constructs, and many others. Following a particular coding style consistently will make your source code more readable.

There are many coding standards available (search "C coding style"), but we suggest you consult the lightweight Linux kernel coding style (see coding-style). The relevant sections are Sections 1, 2, 3, 4, 6, and 8. Note that you do not have to follow every recommendation you can find in a coding style document, you just have to apply that style consistently.

Task 1: Core [25 Marks]

Implement a function with the prototype 
    int editor_insert_char(char editing_buffer[], int editing_buflen,
                           char to_insert, int pos);

which will insert the character to_insert at index pos of editing_buffer. The size of editing_buffer is editing_buflen. When a character is inserted at index pos, each of the original characters at index pos until the end of the buffer must be moved by one position to the right. The last character is thrown out. The function should return 1 if the character insertion occurred, otherwise it should return 0.

For example, if editing_buflen is 16 and the contents of editing_buffer are

pic.png

after executing 
    int r = editor_insert_char(editing_buffer, 16, 's', 12);
the value of r should be 1 and contents of editing_buffer should be

pic01.png

right You can test your implementation by compiling editor.c together with t1test.c (provided under the files directory). If everything goes well, this will generate an executable file t1test. To see if your implementation is correct, run t1test and compare the expected and actual buffer contents and return values. If they match, it means your implementation passes the test. You are free to modify t1test.c if you want to add in more test cases.

Task 2: Core [25 Marks]

Implement a function with the prototype 
    int editor_delete_char(char editing_buffer[], int editing_buflen,
                           char to_delete, int offset);

which will delete the first occurrence of the character to_delete. The search should start from index offset of editing_buffer. The size of editing_buffer is editing_buflen. When a character is deleted at index pos, each of the original characters at index pos until the end of the buffer must be moved by one position to the left. A null character ('\0') is inserted at the end of the buffer. The function should return 1 if the character deletion occurred, otherwise, it should return 0.

For example, if editing_buflen is 16 and the contents of editing_buffer are

pic02.png

after executing 
    int r = editor_delete_char(editing_buffer, 16, 'o', 6);
the value of r should be 1 and the contents of editing_buffer should be

pic03.png

right You can test your implementation by compiling editor.c together with t2test.c (provided under the files directory). Make sure that editor.c and t2test.c are in the same directory. If everything goes well, this will generate an executable file t2test. To see if your implementation is correct, run t2test and compare the expected and actual buffer contents and return values. If they match, it means your implementation passes the test. You are free to modify t2test.c if you want to add in more test cases.

Task 3: Completion [20 Marks]

Implement a function with the prototype 
    int editor_replace_str(char editing_buffer[], int editing_buflen, const char *str, const char *replacement, int offset);
which will replace the first occurrence of the string str with replacement.

The search for the first occurrence should start from index offset of editing_buffer. The size of editing_buffer is editing_buflen.

The replacement should not overwrite other contents in the buffer. This means that if replacement is longer than str, there is a need to move the characters after str to the right. Likewise, if replacement is shorter than str, there is a need to move the characters after str to the left. When moving characters to the right, throw out characters that will not fit in the buffer and when moving characters to the left, insert null characters in the vacated positions.

If str is empty (regardless of the value of replacement), no string replacement should occur. If replacement is empty, then this is the same as deleting the string str.

If the replacement text will go beyond the limits of editing_buffer, then replacement should only occur until the end of editing_buffer.

Ensure that the last character in the buffer is always the null character.

If the string replacement occurred, the function should return the index corresponding to the last letter of replacement in editing_buffer, otherwise, it should return -1. If the replacement text will go beyond the limits of editing_buffer, the function should return editing_buflen-1.

For example, if editing_buflen is 16 and the contents of editing_buffer are

pic04.png

After executing 
  int r = editor_replace_str(editing_buffer, 16, "World!", "there", 0);
the value of r should be 11 (which is the index of the last 'e' in "there") and the contents of editing_buffer should be

pic05.png

right You can test your implementation by compiling editor.c together with t3test.c (provided under the files directory). Make sure that editor.c and t3test.c are in the same directory. If everything goes well, this will generate an executable file t3test. To see if your implementation is correct, run t3test and compare the expected and actual buffer contents and return values. If they match, it means your implementation passes the test. You are free to modify t3test.c if you want to add in more test cases.

Marking Criteria for Part 2:

Criteria Weight Expectations for Full Marks
Compilation 5% Compiles without warnings
Comments 10% Sufficient and appropriate comments
Code Quality 15% Consistent coding style
Correctness 70% Handles all test cases correctly
  100%  

For the Correctness criteria, the following table shows the marks distribution over the different task types:

Task Type Marks
Core (task 1) 25
Core (task 2) 25
Completion (task 3) 20
Total 70
Print version | Backlinks |