CS 246 Assignment 2

Like all assignments, you will complete this assignment via GitHub. See the submission instructions for how to get the starter code and how to submit this assignment.

(If you end up with the assignment files in a .zip file, you can say unzip xxx.zip to unzip it, where xxx.zip is the name of your downloaded file. As always, make sure you are in the right working directory. Use ls and pwd to see where you are.)

cat

Edit the file cat.c to reimplement the command-line tool cat. By default, cat simply repeats what it reads in. We don’t yet know about reading from files, so we will just mimic behavior, by printing out precisely what is read in.

Use getchar to read in individual characters and print them out.

Your program should keep running until it reads end-of-file, which is indicated by a -1 return value from getchar. You can produce an end-of-file on the command line by typing Ctrl+D on an empty line.

Note that the terminal intermediates a bit between you and your program: your program will not repeat the characters as you type them, but only when you press <Enter>. This is because the terminal delivers the characters to a C program only after you press return, and is expected behavior.

If you’re not sure how your program should behave, just run cat without any arguments. Behave like that cat.
SHOUTER

Edit the file shout.c to be like the program above, but changing all letters to uppercase. Detect letters by using the isalpha function, but do not use toupper. Instead, use arithmetic on characters to perform the conversion. See the section Character-Handling Functions on page 138 of King.
SCREAMER

Edit the file scream.c to behave identically like the program above, but do not capitalize using arithmetic. Instead, consult an ASCII table (like in King’s Appendix E, but also available across the internet). Write out the bits used to represent 'A' and the bits used to represent 'a'. What’s the difference? Is the same difference apparent when looking at 'B' and 'b'? Figure out how to use bit-flicking operations (as covered in Section 20.1 of King) to make a letter uppercase, and use this technique to write your program.
wc

Reimplement the utility wc by reading in characters using getchar and reporting how many characters, words, and lines have been read. Whitespace (which separates all words) can be detected by isspace. Lines are separated by newlines ('\n').

For example, if you type the following in (followed by Ctrl+D),
```
One of the main causes of the fall of the Roman Empire was that–--lacking zero–--they
had no way to indicate successful termination of their C programs.
  -- Robert Firth
```
your program should produce
```
175
29
3
```
Note that an empty input (an immediate Ctrl+D) should produce three 0s.

Recall that you can use \< and on the command line to provide a file as input to a program, if you want to test larger inputs. (This is described on p. 54 of Shotts.)

If you’re uncertain how your program should behave, check against the real wc (which prints its answers out in the opposite order from what I am asking here).
Converter: decimal to hex

Write a program (in conv_dec.c) that reads in a number and prints out the hexadecimal version of that number. The catch is that the input must be read as characters. Use a loop with getchar to read in characters until a newline is spotted. As the characters are read in, use some math (hint: multiply by 10 in a key spot) to compute the number the user has written. Then print out that number in hex—but with another catch: no printf. Instead, convert the value to hexadecimal yourself, printing out the characters (with putchar) backwards. (The “backwards” bit is to make this easier, actually!) Output a newline before the program exits.

For example, if I enter
```
123
```
my program outputs
```
B7
```
because 0x7B equals 123. Note that the output is written backwards.

This program should use no I/O functions other than getchar and putchar.
Converter: hex to octal

Write a program (in `conv_hex.c`) that reads in a number in hexadecimal and prints it
out in octal. Like the last program, you will use only `putchar` and `getchar`. However,
unlike the last program, *both* the input and the output are reversed. (Again, this makes
it *easier*.) In addition, your program must be able to handle arbitrarily large numbers.
Do this by converting "on the fly" -- do not read in all of a user's input, figure out
the value, and then convert to octal. Instead, take advantage of the similarity between
hexadecimal and octal and convert as you read, with only one loop.

For example, if I enter

    AB320D54

my program outputs

    27612046501

This is challenging problem. You will get partial credit if your program works only
up to a maximum.

Reflections

Edit refl.txt (short for “reflections”) to answer the questions therein.

When you’re all done, submit on GitHub by creating a Pull Request according to these instructions.