ENCM 335 Fall 2018 Lab 6 for the Week of October 22 Complete Instructions

Transcription

1 page 1 of 5 ENCM 335 Fall 2018 Lab 6 for the Week of October 22 Complete Instructions Steve Norman Department of Electrical & Computer Engineering University of Calgary October 2018 Lab instructions and other documents for ENCM 335 can be found at Administrative details Each student must hand in their own assignment Later in the course, you may be allowed to work in pairs on some assignments. ATTENTION: Unusual Due Date Because most students in ENCM 335 have multiple midterms in the weeks of October 22 and October 29, I m allowing a little bit of extra time to complete this lab. The Due Date for this assignment is 3:30pm Monday, October 29. There is no Late Due Date, because solutions will be posted late in the afternoon on October 29, to help you study for the midterm on November 1. Marking scheme A B C D total unmarked 18 marks How to package and hand in your assignments Please see the information in the Lab 1 instructions. Exercise A: A memory diagram with pointers and structure objects This exercise is unmarked.

2 ENCM 335 Fall 2018 Lab 6 (complete) page 2 of 5 It s important to be clear about whether a pointer points to an entire structure or to some item within a structure object. Be careful to get each arrowhead you draw right on the edge of whatever box is appropriate. Download the file lab6exa.c. Make a memory diagram for point one. There is nothing to hand in. You can check your work against a solution that will be posted no later than Monday evening, October 22. Exercise B: Another memory diagram with structure objects The program you ll look at in this exercise shows why using structure types hold date/time-of-day combinations is really awful if you want to be able to compare one such combination to another to decide which is earlier. It s much better to describe date/time-of-day combinations using a number of elapsed seconds since some past date and time of day that makes operations such as comparisons, addition, and subtraction much easier and faster. (Systems derived from Unix, such as Linux and macos, use seconds elapsed since time 00:00:00 UTC, January 1, 1970.) Download the file lab6exb.c and read it carefully. Make a diagram of the stack for point one. Hand in your diagram. (You may want to make a copy of your diagram before you hand it in, so you can check your work against the posted solution before the midterm.) Exercise C: Simple text file output This exercise will have you write code to create some small, simple text files. The exercise is designed to give you practice with the fopen, fprintf, and fclose functions. You may want to review lecture slides notes on text file output before you work on this exercise. Here s a helpful tip: A command called less is useful for viewing text files in Cygwin or macos terminal windows. For example, less foo.txt would allow you to view the file foo.txt. To get out of less, press the q key. To get help about all the commands within less, press the h key.

3 ENCM 335 Fall 2018 Lab 6 (complete) page 3 of 5 Download all three files from the directory for this exercise. Study the code and comments in all three files, then build an executable with the command gcc -Wall main6c.c vec6c.c (Note that.h files are not listed in a command to build an executable, as that kind of file will be found using #include directives.) Run the executable. Replace the code in the definitions of save_precisely and save_fancily with code that will make the functions do what is specified in their function interface comments. In the precise format, the number of elements is given in the first line of output, and double values are printed in scientific notation with 20 digits after the decimal place. (The % conversion for that in printf and fprintf is %.20e.) For example, if an array of vectors is set up as vec_t arr[ ] = { {-1.0, 0.0, 0.5}, {1.1, 2.2, -3.3}, {0.01, , 0.5}, {0.75, 0.76, } }; then the corresponding output file should look like this e e e e e e e e e e e e+01 (By the way, some of the output shows that some numbers that can be represented exactly in base ten can t be represented exactly in the base two system used for the double type on most computers.) The fancy format doesn t print the number of array elements, but it does put an element index on each line. It uses parentheses and commas to group vector components together, and uses %.4f to print each double. Here is the fancy output file for the earlier example array: element 0: ( , , ) element 1: (1.1000, , ) element 2: (0.0100, , ) element 3: (0.7500, , ) Hand in printouts of the final version of vec6d.c and all four text files that will be produced by running your program. Exercise D: Simple text file input Please review lecture notes on text file input from Wednesday, October 17 and Monday, October 22 that material is highly relevant to this exercise!

4 ENCM 335 Fall 2018 Lab 6 (complete) page 4 of 5 Read This Second Lecture notes have not discussed using scanf or fscanf to read input as a series of whitespace-separated tokens, so I ll explain how that works here. First, here s an example what not to do. Suppose that fp is of type FILE*, and points to a FILE object that has been opened for input... char b[20]; int nscan; nscan = fscanf(fp, "%s", b); // DANGER! The problem in the above use of fscanf is that fscanf is not told the size of the array b, and a buffer overflow will occur if there is a sequence of 20 or more non-whitespace characters in the input stream. This is a safe way to get a string using fscanf: char b[20]; int nscan; nscan = fscanf(fp, "%19s", b); // Will not read more than 19 chars. The above function call will consume and discard whitespace until a non-whitespace character is found. Then, usually, it will make a string in the array b by copying consecutive non-whitespace input characters into the array until either a whitespace character is found in the input, or 19 characters have been copied into the array. In either case, nscan will get a value of 1. For example, suppose the input sequence looks like this, where represents a space: AB CDE The call to fscanf will put A, B, and \0 into b[0], b[1], and b[2]. The first character to be read by the next input operation with fp will be the first of the two spaces between B and C in the input stream. In the case that fscanf finds nothing but whitespace until the end of a file, it will return EOF. Of course the numbers 19 and 20 in the code above are just examples. In general, the value of n in "%ns" should be one less than the size of the array that is to receive the string, to allow room for a terminating \0. Download both of the files from the directory for this exercise. Have a look at the_text.txt, which is text from a lecture slide, with punctuation removed to make the job of counting words relatively easy. Edit the code in the.c file so that the main function does this: attempts to open the file the_text.txt for input; prints an error message and calls exit if the file was not opened; reads the whole input file, counting words and keeping track of the longest and shortest words seen so far; closes the file; reports the word count and the longest and shortest words. This is what the output should look like: word count: 95 longest word: programming (11 letter(s)) shortest word: C (1 letter(s))

5 ENCM 335 Fall 2018 Lab 6 (complete) page 5 of 5 Hand in a printout of your completed.c file.