COMS W3157 Advanced Programming, Lab #2
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Please read this assignment carefully and follow the instructions
EXACTLY.
Submission
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Please refer to the lab retrieval and submission instruction, which outlines
the only way to submit your lab assignments. Please do not email me your
code.
If a lab assignment consists of multiple parts, your code for each part must
be in a subdirectory (named “part1”, “part2”, etc.)
Please make sure that your submission satisfies the requirements for the
following items:
– README.txt
– Makefile
The requirements remain the same as lab 1.
Valgrind
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There is another requirement that applies to all labs starting lab 2.
You will be heavily penalized if your program contains memory errors.
Memory errors include (among other things) failure to call free() on the
memory you obtained through malloc(), accessing past array bounds,
dereferencing uninitialized pointers, etc.
You can use a debugging tool called “valgrind” to check your program:
valgrind –leak-check=yes ./your_executable
It will tell you if your program has any memory error. See “The Valgrind
Quick Start Guide” at http://valgrind.org/docs/manual/quick-start.html for
more info.
You must include the output of the valgrind run for EACH PART in your
README.txt. In addition, TAs will run valgrind on your program when
grading.
You can include the valgrind output in your README.txt as follows. If
you¡¯re in your part1 directory, for example, issue the following command:
valgrind –leak-check=yes ./your_program >> ../README.txt 2>&1
The command will append the valgrind output at the end of your README.txt.
Make sure you put “>>”, not “>”. If you type “>”, it will overwrite your
README.txt.
Part 1: Sorting an integer array
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Write a program that dynamically allocates an array of integers. The size
of the array (the number of integers, not the byte size) should be read from
the user using scanf(). You may assume that the user will input a positive
integer (i.e., don¡¯t do error checking). The elements of the array should
be filled using random() function. After filling the array with random
numbers, your program should then make a copy of the array, and sort the new
array in ascending order: that is, the first entry of the array should
contain the smallest integer in the array, while the last entry should
contain the largest integer in the array. Then make a second copy of the
original array, and sort it in descending order. Finally your program
should print out all three arrays. All three arrays should be separately
allocated using malloc() library function. Don¡¯t forget to call free() to
deallocate the arrays.
You should always check the return value of malloc(), and if it¡¯s
NULL, print an error message and quit the program, like this:
p = malloc(1000000000);
if (p == NULL) {
perror(“malloc returned NULL”);
exit(1); }
Make sure you do this everytime you call malloc(). This applies to
all labs in this class.
Please name your executable program “isort”.
Type “man 3 random” to read the man page for random(). In K&R2, there is no
mention of random(). Instead, it describes the older and inferior rand()
function. The usage is the same. Use random() in your code.
The random() function returns a non-negative integer in the range from 0 to
2^31-1. In order to make the visual inspection of the output a little
easier, please convert the large random integer to one in the range from 0
to 99. Please print the arrays in the following format:
original: 31 57 1 44
ascending: 1 31 44 57
descending: 57 44 31 1
You will notice that random() function always returns the same
sequence of integers. It¡¯s just a pseudo-random number generator that
simulates randomness. You can “seed” the random number generator by
calling srandom() function once in the beginning of your program.
Calling it with the return value of time(NULL) will ensure a different
sequence of random numbers everytime the program is run. You should
do that.
For sorting, you have two options. You can implement any sorting
algorithm yourself. You are allowed to look up on the Internet or any
book for a sorting algorithm. If you do, please cite the source in
the comment for the function.
Or you can use qsort() function provided by the standard C library
(just like they provide printf()). Using the qsort() library function
is simpler, but requires that you know how to use pointers to
functions, which we have not covered yet. Section 5.11 of K&R2
describes pointers to functions. Unfortunately, the section uses a
sorting function named “qsort” to illustrate pointers to functions,
but it takes a different set of parameters than the real qsort() of
standard library. The standard library version of qsort() is
described on page 253, K&R2, or in the man page (type “man 3 qsort”).
There is, however, one little requirement about calling the sorting
function, whether it¡¯s your own function or the qsort() function. I
want you to call your sorting function indirectly through the
following function:
/* This function sorts an integer array.
begin points to the 1st element of the array.
end points to ONE PAST the last element of the array.
If ascending is 1, the array will be sorted in ascending order.
If ascending is 0, the array will be sorted in descending order.
*/
void sort_integer_array(int *begin, int *end, int ascending)
{
/* In here, you will call your real sorting function (your own
* or the qsort()). Basically, I want to make sure that you
* know how to translate the begin/end parameter to whatever
* is required for your sorting function.
*/
… }
Part 2: echo with a twist
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Write a program, named “twecho”, that takes words as command line
arguments, and prints each word twice, once as is and once
all-capitalized, separated by a space. For example,
./twecho hello world dude
should output:
hello HELLO
world WORLD
dude DUDE
Your program should handle any number of arguments. You can receive
the command line arguments if you start your main() function in the
following way:
int main(int argc, char **argv)
Please refer to section 5.10 in K&R2. In particular, the picture on
page 115 depicts clearly how the command line argument strings are
stored in memory.
Here are some requirements and hints:
– You must use the main() function exactly as given below. You CANNOT
modify the main function. Your job is to implement other functions
that main() calls.
int main(int argc, char **argv)
{
if (argc <= 1)
return 1;
char **copy = duplicateArgs(argc, argv);
char **p = copy;
argv++;
p++;
while (*argv) {
printf("%s %s\n", *argv++, *p++);
}
freeDuplicatedArgs(copy);
return 0; }
- You will probably need the following #includes:
#include
#include
#include
#include
– You can put duplicateArgs() and freeDuplicatedArgs() in the same .c
file as main().
– In duplicateArgs() function, you are making a “copy” of the memory
structure shown in the picture on page 115, K&R2. You will call
malloc() once for the overall array where each element is of type
char*, then you will call malloc() for each element of that array,
each of which will hold the all-cap version of each argument. Of
course, you will have to copy each string character-by-character,
capitalizing as you go.
Some useful library functions for doing this include strlen() and
toupper(). See the textbook.
Don¡¯t forget that the last element of the overall array of char*¡¯s
is a NULL pointer (see the picture in page 115, K&R2).
– In freeDuplicatedArgs() function, you must free() everything you
malloc()ed. First free() all individual strings, and then free()
the overall array.
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Good luck!