This repository contains examples and exercises from the second edition K&R.
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Compiled using gcc version 8.3.0 on Debian 10 x86_64
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A return type is explicitly set on the main function to clear a
gccwarning 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.
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
$
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
$
This example incorporates comments, declaring variables, variable assignments, the while loop, and displaying arithmetic results into stdout.
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.
Conform to the textbook example, using better formatting and floating-point numbers throughout the equation.
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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.
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.
This is a simple little solution for a Celsius to Fahrenheit table.
Textbook example of counting lines, words, and characters from input.
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 $