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220 lines
6.4 KiB
Plaintext
220 lines
6.4 KiB
Plaintext
Notes on K&R C (2nd edition)
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----------------------------
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This repository contains examples and exercises from the
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https://en.wikipedia.org/wiki/The_C_Programming_Language[second edition K&R.]
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- Compiled using gcc version 8.3.0 on Debian 10 x86_64
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01-hello-world.c
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~~~~~~~~~~~~~~~~
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https://github.com/krislamo/knrc/commit/3e078042a42fed15b4de1b8ff31834f952ef5d81[(Diff)]
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https://github.com/krislamo/knrc/blob/3e078042a42fed15b4de1b8ff31834f952ef5d81/01-hello-world.c[(Source)]
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- A return type is explicitly set on the main function to clear a `gcc` warning in a slight deviation
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from the book.
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This example demonstrates an understanding of how to compile source code
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to machine code. It includes the `01-hello-world.c` source file and a `Makefile` that
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executes a `gcc` command to compile. In addition, a `.gitignore` file is included in
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the `./bin` directory to keep binary artifacts out of version control.
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Exercise 1-1: leave out parts
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^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
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While these omissions are not directly included in the source, here are some examples of
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leaving parts out to generate compilation errors or warnings.
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Removing braces:
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----
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$ sed -i 's/[{}]//g' 01-hello-world.c
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$ make
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gcc -o ./bin/01-helloworld 01-hello-world.c
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01-hello-world.c: In function ‘main’:
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01-hello-world.c:5:2: error: expected declaration specifiers before ‘printf’
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printf("hello, world\n");
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^~~~~~
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01-hello-world.c:6: error: expected ‘{’ at end of input
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make: *** [Makefile:4: hello] Error 1
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----
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Removing the semicolon:
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----
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$ sed -i 's/[;]//g' 01-hello-world.c
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$ make
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gcc -o ./bin/01-helloworld 01-hello-world.c
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01-hello-world.c: In function ‘main’:
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01-hello-world.c:5:26: error: expected ‘;’ before ‘}’ token
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printf("hello, world\n")
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^
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;
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}
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~
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make: *** [Makefile:4: hello] Error 1
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----
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Removing the include directive:
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----
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$ sed -i 's/#include.*//g' 01-hello-world.c
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$ make
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gcc -o ./bin/01-helloworld 01-hello-world.c
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01-hello-world.c: In function ‘main’:
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01-hello-world.c:5:2: warning: implicit declaration of function ‘printf’ [-Wimplicit-function-declaration]
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printf("hello, world\n");
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^~~~~~
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01-hello-world.c:5:2: warning: incompatible implicit declaration of built-in function ‘printf’
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01-hello-world.c:5:2: note: include ‘<stdio.h>’ or provide a declaration of ‘printf’
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01-hello-world.c:1:1:
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+#include <stdio.h>
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01-hello-world.c:5:2:
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printf("hello, world\n");
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^~~~~~
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$ ./bin/01-helloworld
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hello, world
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$
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----
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Exercise 1-2: unknown escapes in printf
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^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
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Adding a `\k` into printf:
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----
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$ sed -i 's/\\n/\\k\\n/g' 01-hello-world.c
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$ make
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gcc -o ./bin/01-helloworld 01-hello-world.c
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01-hello-world.c: In function ‘main’:
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01-hello-world.c:5:9: warning: unknown escape sequence: '\k'
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printf("hello, world\k\n");
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^~~~~~~~~~~~~~~~~~
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$ ./bin/01-helloworld
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hello, worldk
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$
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----
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02-vars-and-math.c
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~~~~~~~~~~~~~~~~~~
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https://github.com/krislamo/knrc/commit/9a193d84f112aa2bdfccc6c5137ce95aeccb1ead[(Diff)]
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https://github.com/krislamo/knrc/blob/9a193d84f112aa2bdfccc6c5137ce95aeccb1ead/02-vars-and-math.c[(Source)]
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This example incorporates comments, declaring variables, variable assignments, the
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while loop, and displaying arithmetic results into stdout.
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Higher precision
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^^^^^^^^^^^^^^^^^
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https://github.com/krislamo/knrc/commit/e7e2367bd7342302de7befacd90761671ebfe0bf[(Diff)]
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https://github.com/krislamo/knrc/blob/e7e2367bd7342302de7befacd90761671ebfe0bf/02-vars-and-math.c[(Source)]
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After typing out the second program's source, I instantly noticed a lack of floating-point
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numbers (from previous knowledge). So, impatiently, I came up with a solution for a cleaner
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and higher precision conversion table before seeing the book's answer. This slight change
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involved changing the variables' type to `float` and changing `%d` to `%g` in printf.
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Match textbook formatting
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^^^^^^^^^^^^^^^^^^^^^^^^^
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https://github.com/krislamo/knrc/commit/0d48636cdcdd5bc47e30fa6de21a1b8dcab7ec32[(Diff)]
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https://github.com/krislamo/knrc/blob/0d48636cdcdd5bc47e30fa6de21a1b8dcab7ec32/02-vars-and-math.c[(Source)]
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Conform to the textbook example, using better formatting and floating-point numbers
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throughout the equation.
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The for loop
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^^^^^^^^^^^^
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https://github.com/krislamo/knrc/commit/8ba629852ea914d74a28d0410e8a14aaf9724981[(Diff)]
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https://github.com/krislamo/knrc/blob/8ba629852ea914d74a28d0410e8a14aaf9724981/02-vars-and-math.c[(Source)]
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- I skipped over exercises 1-3 and 1-4 into the for loop in a slip-up
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Here we simplify the code into a for loop, removing all but one variable.
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Exercise 1-3: print a heading
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^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
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https://github.com/krislamo/knrc/commit/0893987235ce02329c87ea000fb97eb0688bea54[(Diff)]
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https://github.com/krislamo/knrc/blob/0893987235ce02329c87ea000fb97eb0688bea54/02-vars-and-math.c[(Source)]
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I add a heading above the table with an additional printf statement and made a slight adjustment in
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the original printf to align it better.
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Exercise 1-4. print Celsius to Fahrenheit table
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^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
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https://github.com/krislamo/knrc/commit/93126a8207ba83e3712bbab7b1e54548761a5fa1[(Diff)]
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https://github.com/krislamo/knrc/blob/93126a8207ba83e3712bbab7b1e54548761a5fa1/03-celsius-to-fahrenheit.c[(Source)]
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This is a simple little solution for a Celsius to Fahrenheit table.
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Exercise 1-5. print the table in reverse order
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^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
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https://github.com/krislamo/knrc/commit/588969b09fabab1e91ff4f4b1c37e87fc23cf76b[(Diff)]
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https://github.com/krislamo/knrc/blob/588969b09fabab1e91ff4f4b1c37e87fc23cf76b/02-vars-and-math.c[(Source)]
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Move some numbers around to reverse the table.
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09-word-count.c
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~~~~~~~~~~~~~~~~
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https://github.com/krislamo/knrc/commit/d064db2b171e3da74fd5082ae29456f64caeafeb[(Diff)]
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https://github.com/krislamo/knrc/blob/d064db2b171e3da74fd5082ae29456f64caeafeb/09-word-count.c[(Source)]
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Textbook example of counting lines, words, and characters from input.
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Exercise 1-11: test the word count program
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^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
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No input:
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----
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$ ./bin/09-word-count
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0 0 0
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$
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----
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Just 3 newlines:
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----
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$ ./bin/09-word-count
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3 0 3
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$
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----
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Just 3 tabs:
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----
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$ ./bin/09-word-count
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0 0 3
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$
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----
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Just 3 spaces:
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----
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$ ./bin/09-word-count
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0 0 3
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$
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----
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Just a single word per line:
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----
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$ ./bin/09-word-count
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one
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word
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per
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line
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4 4 18
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$
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----
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Three blanks before and after:
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----
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$ ./bin/09-word-count
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three blanks before/after 0 3 31
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$
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----
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