Lab 5 -- More Pointers and Arrays

Reference solutions to all programs are available on mogul in /home/cs381/labs/pointers2.

Have a look at this example, which demonstrates some of the ways we can declare, construct, initialize, and otherwise use arrays in C.

The comments in this program describe its usage of the most important C features. Pay special attention to the usage of malloc to allocate chunks of memory and free to return them to the system when finished. It also shows the use of realloc to change the size of an allocated chunk of memory.

This demonstrates one of the key differences between C and Java: we have to tell C when we are finished with our allocated memory. Java uses garbage collection to reclaim memory no longer in use automatically. We will consider the merits of both approaches later in the semester; for now we simply need to remember that any memory we allocate in C must be released when we are done with it. Advice: when you add a malloc(), immediately add the corresponding free() in an appropriate place.

Question 1: Draw a series of memory diagrams showing the state of the stack and heap variables in existence and their values (indicate unintialized values with a "?") at the execution points labeled with comments as "EXECUTION POINT"s A, B, C, and D. (8 points)

Question 2: Explain the purpose of each component of the malloc statement on line 58 of arrays.c:

b = (double *)malloc(10*sizeof(double));

(2 points)

Question 3: Explain how the "while (*f)" loop that starts on line 117 of arrays.c works. What would happen if the first element of the array was a 0? What would happen if there was no 0 value in the array at all? (4 points)

Practice Program: Extend your input adder program to remember all the values read in by storing them in a dynamically-allocated array. Name your program inputsortadder.c. At the end, the program should print the addition problem and its solution, first with the numbers in the same order as entered, then sorted in increasing order (you might use the isort function from last time). For example, given the input values 9, 4, and 5, the program would print

9+4+5=18
4+5+9=18

Your task here is to be able to create the array and continue to make it larger as needed. Start with a reasonably-sized array (perhaps 10 slots). If the user inputs 10 or fewer values, you are all set. But if an 11th value is input, you will need to resize the array to make space. Use the same strategy as Java's Vector or ArrayList class - double the size of the array each time it fills. (10 points)

We have seen that strings in C are simply represented as NULL-terminated arrays of char. The following example demonstrates more about this and gives examples of some of C's string processing functions.

Also read the man page for string(3). It lists the string processing functions available in the standard C library.

Practice Program: K&R Exercise 5-4. Call your program strend.c and include a main function that tests your program by passing the first two command-line parameters to main as the parameters s and t to your function. (6 points)

Please submit all required files as email attachments to terescoj AT strose.edu by Thursday, December 31, 2015. Be sure to check that you have used the correct file names and that your submission matches all of the submission guidelines listed on the course home page. In order to email your files, you will need to transfer them from mogul to the computer from which you wish to send the email. There are a number of options, including the sftp command from the Mac command line.

Grading Breakdown
Lab questions	14 points
Practice program `inputsortadder.c` correctness	10 points
Practice program `strend.c` correctness	6 points
Total	30