knrc/README.adoc

Notes on K&R C (2nd edition)
----------------------------
This repository contains examples and exercises from the
https://en.wikipedia.org/wiki/The_C_Programming_Language[second edition K&R.]

- Compiled using gcc version 8.3.0 on Debian 10 x86_64

01-hello-world.c
~~~~~~~~~~~~~~~~
https://github.com/krislamo/knrc/commit/3e078042a42fed15b4de1b8ff31834f952ef5d81[(Diff)]
https://github.com/krislamo/knrc/blob/3e078042a42fed15b4de1b8ff31834f952ef5d81/01-hello-world.c[(Source)]

- A return type is explicitly set on the main function to clear a `gcc` warning in a slight deviation
from the book.

This example demonstrates an understanding of how to compile source code
to machine code. It includes the `01-hello-world.c` source file and a `Makefile` that
executes a `gcc` command to compile. In addition, a `.gitignore` file is included in
the `./bin` directory to keep binary artifacts out of version control.

Exercise 1-1: leave out parts
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
While these omissions are not directly included in the source, here are some examples of
leaving parts out to generate compilation errors or warnings.

Removing braces:

----
$ sed -i 's/[{}]//g' 01-hello-world.c
$ make
gcc -o ./bin/01-helloworld 01-hello-world.c
01-hello-world.c: In function ‘main’:
01-hello-world.c:5:2: error: expected declaration specifiers before ‘printf’
  printf("hello, world\n");
  ^~~~~~
01-hello-world.c:6: error: expected ‘{’ at end of input


make: *** [Makefile:4: hello] Error 1
----

Removing the semicolon:

----
$ sed -i 's/[;]//g' 01-hello-world.c
$ make
gcc -o ./bin/01-helloworld 01-hello-world.c
01-hello-world.c: In function ‘main’:
01-hello-world.c:5:26: error: expected ‘;’ before ‘}’ token
  printf("hello, world\n")
                          ^
                          ;
 }
 ~
make: *** [Makefile:4: hello] Error 1
----

Removing the include directive:

----
$ sed -i 's/#include.*//g' 01-hello-world.c
$ make
gcc -o ./bin/01-helloworld 01-hello-world.c
01-hello-world.c: In function ‘main’:
01-hello-world.c:5:2: warning: implicit declaration of function ‘printf’ [-Wimplicit-function-declaration]
  printf("hello, world\n");
  ^~~~~~
01-hello-world.c:5:2: warning: incompatible implicit declaration of built-in function ‘printf’
01-hello-world.c:5:2: note: include ‘<stdio.h>’ or provide a declaration of ‘printf’
01-hello-world.c:1:1:
+#include <stdio.h>

01-hello-world.c:5:2:
  printf("hello, world\n");
  ^~~~~~
$ ./bin/01-helloworld
hello, world
$
----

Exercise 1-2: unknown escapes in printf
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

Adding a `\k` into printf:

----
$ sed -i 's/\\n/\\k\\n/g' 01-hello-world.c
$ make
gcc -o ./bin/01-helloworld 01-hello-world.c
01-hello-world.c: In function ‘main’:
01-hello-world.c:5:9: warning: unknown escape sequence: '\k'
  printf("hello, world\k\n");
         ^~~~~~~~~~~~~~~~~~
$ ./bin/01-helloworld
hello, worldk
$
----

02-vars-and-math.c
~~~~~~~~~~~~~~~~~~
https://github.com/krislamo/knrc/commit/9a193d84f112aa2bdfccc6c5137ce95aeccb1ead[(Diff)]
https://github.com/krislamo/knrc/blob/9a193d84f112aa2bdfccc6c5137ce95aeccb1ead/02-vars-and-math.c[(Source)]

This example incorporates comments, declaring variables, variable assignments, the
while loop, and displaying arithmetic results into stdout.

Higher precision
^^^^^^^^^^^^^^^^^
https://github.com/krislamo/knrc/commit/e7e2367bd7342302de7befacd90761671ebfe0bf[(Diff)]
https://github.com/krislamo/knrc/blob/e7e2367bd7342302de7befacd90761671ebfe0bf/02-vars-and-math.c[(Source)]

After typing out the second program's source, I instantly noticed a lack of floating-point
numbers (from previous knowledge). So, impatiently, I came up with a solution for a cleaner
and higher precision conversion table before seeing the book's answer. This slight change
involved changing the variables' type to `float` and changing `%d` to `%g` in printf.

Match textbook formatting
^^^^^^^^^^^^^^^^^^^^^^^^^
https://github.com/krislamo/knrc/commit/0d48636cdcdd5bc47e30fa6de21a1b8dcab7ec32[(Diff)]
https://github.com/krislamo/knrc/blob/0d48636cdcdd5bc47e30fa6de21a1b8dcab7ec32/02-vars-and-math.c[(Source)]

Conform to the textbook example, using better formatting and floating-point numbers
throughout the equation.

The for loop
^^^^^^^^^^^^
https://github.com/krislamo/knrc/commit/8ba629852ea914d74a28d0410e8a14aaf9724981[(Diff)]
https://github.com/krislamo/knrc/blob/8ba629852ea914d74a28d0410e8a14aaf9724981/02-vars-and-math.c[(Source)]

- I skipped over exercises 1-3 and 1-4 into the for loop in a slip-up

Here we simplify the code into a for loop, removing all but one variable.

Exercise 1-3: print a heading
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
https://github.com/krislamo/knrc/commit/0893987235ce02329c87ea000fb97eb0688bea54[(Diff)]
https://github.com/krislamo/knrc/blob/0893987235ce02329c87ea000fb97eb0688bea54/02-vars-and-math.c[(Source)]

I add a heading above the table with an additional printf statement and made a slight adjustment in
the original printf to align it better.

Exercise 1-4. print Celsius to Fahrenheit table
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
https://github.com/krislamo/knrc/commit/93126a8207ba83e3712bbab7b1e54548761a5fa1[(Diff)]
https://github.com/krislamo/knrc/blob/93126a8207ba83e3712bbab7b1e54548761a5fa1/03-celsius-to-fahrenheit.c[(Source)]

This is a simple little solution for a Celsius to Fahrenheit table.

Exercise 1-5. print the table in reverse order
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
https://github.com/krislamo/knrc/commit/588969b09fabab1e91ff4f4b1c37e87fc23cf76b[(Diff)]
https://github.com/krislamo/knrc/blob/588969b09fabab1e91ff4f4b1c37e87fc23cf76b/02-vars-and-math.c[(Source)]

Move some numbers around to reverse the table.

09-word-count.c
~~~~~~~~~~~~~~~~
https://github.com/krislamo/knrc/commit/d064db2b171e3da74fd5082ae29456f64caeafeb[(Diff)]
https://github.com/krislamo/knrc/blob/d064db2b171e3da74fd5082ae29456f64caeafeb/09-word-count.c[(Source)]

Textbook example of counting lines, words, and characters from input.

Exercise 1-11: test the word count program
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

No input:

----
$ ./bin/09-word-count
0 0 0
$
----

Just 3 newlines:

----
$ ./bin/09-word-count



3 0 3
$
----

Just 3 tabs:

----
$ ./bin/09-word-count
                        0 0 3
$
----

Just 3 spaces:

----
$ ./bin/09-word-count
   0 0 3
$
----

Just a single word per line:

----
$ ./bin/09-word-count
one
word
per
line
4 4 18
$
----

Three blanks before and after:

----
$ ./bin/09-word-count
   three blanks before/after   0 3 31
$
----