Merge pull request #228 from H2CO3/patch-1

Fix mistakes in the C tutorial

1 files changed, 399 insertions, 279 deletions

diff --git a/c.html.markdown b/c.html.markdown
index 2b50efa0..8e16837c 100644
--- a/c.html.markdown
+++ b/c.html.markdown
@@ -1,23 +1,25 @@
 ---
-name: c
-category: language
-language: c
-filename: learnc.c
-contributors:
-    - ["Adam Bard", "http://adambard.com/"]
+- name: c
+- category: language
+- language: c
+- filename: learnc.c
+- contributors:
+ - [Adam Bard](http://adambard.com/)
+ - [Árpád Goretity](http://twitter.com/H2CO3_iOS)
+
 ---
 
-Ah, C. Still the language of modern high-performance computing.
+Ah, C. Still **the** language of modern high-performance computing.
 
 C is the lowest-level language most programmers will ever use, but
 it more than makes up for it with raw speed. Just be aware of its manual
 memory management and C will take you as far as you need to go.
 
 ```c
-// Single-line comments start with //
+// Single-line comments start with // - only available in C99 and later.
 
 /*
-Multi-line comments look like this.
+Multi-line comments look like this. They work in C89 as well.
 */
 
 // Import headers with #include
@@ -25,6 +27,17 @@ Multi-line comments look like this.
 #include <stdio.h>
 #include <string.h>
 
+// file names between <angle brackets> are headers from the C standard library.
+// They are searched for by the preprocessor in the system include paths
+// (usually /usr/lib on Unices, can be controlled with the -I<dir> option if you are using GCC or clang.)
+// For your own headers, use double quotes instead of angle brackets:
+#include "my_header.h"
+
+// The C preprocessor introduces an almost fully-featured macro language. It's useful, but
+// it can be confusing (and what's even worse, it can be misused). Read the
+// Wikipedia article on the C preprocessor for further information:
+// http://en.wikipedia.org/wiki/C_preprocessor
+
 // Declare function signatures in advance in a .h file, or at the top of
 // your .c file.
 void function_1();
@@ -33,264 +46,347 @@ void function_2();
 // Your program's entry point is a function called
 // main with an integer return type.
 int main() {
-
-// print output using printf, for "print formatted"
-// %d is an integer, \n is a newline
-printf("%d\n", 0); // => Prints 0
-// All statements must end with a semicolon
-
-///////////////////////////////////////
-// Types
-///////////////////////////////////////
-
-// You have to declare variables before using them. A variable declaration
-// requires you to specify its type; a variable's type determines its size
-// in bytes.
-
-// ints are usually 4 bytes 
-int x_int = 0;
-
-// shorts are usually 2 bytes
-short x_short = 0;
-
-// chars are guaranteed to be 1 byte
-char x_char = 0;
-char y_char = 'y'; // Char literals are quoted with ''
-
-// longs are often 4 to 8 bytes; long longs are guaranteed to be at least
-// 64 bits
-long x_long = 0;
-long long x_long_long = 0; 
-
-// floats are usually 32-bit floating point numbers
-float x_float = 0.0;
-
-// doubles are usually 64-bit floating-point numbers
-double x_double = 0.0;
-
-// Integral types may be unsigned. This means they can't be negative, but
-// the maximum value of an unsigned variable is greater than the maximum
-// signed value of the same size.
-unsigned char ux_char;
-unsigned short ux_short;
-unsigned int ux_int;
-unsigned long long ux_long_long;
-
-// Other than char, which is always 1 byte, these types vary in size depending
-// on your machine. sizeof(T) gives you the size of a variable with type T in 
-// bytes so you can express the size of these types in a portable way.
-// For example,
-printf("%lu\n", sizeof(int)); // => 4 (on machines with 4-byte words)
-
-// Arrays must be initialized with a concrete size.
-char my_char_array[20]; // This array occupies 1 * 20 = 20 bytes
-int my_int_array[20]; // This array occupies 4 * 20 = 80 bytes
-                      // (assuming 4-byte words)
-
-
-// You can initialize an array to 0 thusly:
-char my_array[20] = {0};
-
-// Indexing an array is like other languages -- or,
-// rather, other languages are like C
-my_array[0]; // => 0
-
-// Arrays are mutable; it's just memory!
-my_array[1] = 2;
-printf("%d\n", my_array[1]); // => 2
-
-// Strings are just arrays of chars terminated by a NUL (0x00) byte,
-// represented in strings as the special character '\0'.
-// (We don't have to include the NUL byte in string literals; the compiler
-//  inserts it at the end of the array for us.)
-char a_string[20] = "This is a string";
-printf("%s\n", a_string); // %s formats a string
-
-/*
-You may have noticed that a_string is only 16 chars long.
-Char #17 is the NUL byte. 
-Chars #18, 19 and 20 have undefined values.
-*/
-
-printf("%d\n", a_string[16]); // => 0
-
-///////////////////////////////////////
-// Operators
-///////////////////////////////////////
-
-int i1 = 1, i2 = 2; // Shorthand for multiple declaration
-float f1 = 1.0, f2 = 2.0;
-
-// Arithmetic is straightforward
-i1 + i2; // => 3
-i2 - i1; // => 1
-i2 * i1; // => 2
-i1 / i2; // => 0 (0.5, but truncated towards 0)
-
-f1 / f2; // => 0.5, plus or minus epsilon
-
-// Modulo is there as well
-11 % 3; // => 2
-
-// Comparison operators are probably familiar, but
-// there is no boolean type in c. We use ints instead.
-// 0 is false, anything else is true. (The comparison 
-// operators always return 0 or 1.)
-3 == 2; // => 0 (false)
-3 != 2; // => 1 (true)
-3 > 2; // => 1
-3 < 2; // => 0
-2 <= 2; // => 1
-2 >= 2; // => 1
-
-// Logic works on ints
-!3; // => 0 (Logical not)
-!0; // => 1
-1 && 1; // => 1 (Logical and)
-0 && 1; // => 0
-0 || 1; // => 1 (Logical or)
-0 || 0; // => 0
-
-// Bitwise operators!
-~0x0F; // => 0xF0 (bitwise negation)
-0x0F & 0xF0; // => 0x00 (bitwise AND)
-0x0F | 0xF0; // => 0xFF (bitwise OR)
-0x04 ^ 0x0F; // => 0x0B (bitwise XOR)
-0x01 << 1; // => 0x02 (bitwise left shift (by 1))
-0x02 >> 1; // => 0x01 (bitwise right shift (by 1))
-
-///////////////////////////////////////
-// Control Structures
-///////////////////////////////////////
-
-if (0) {
-  printf("I am never run\n");
-} else if (0) {
-  printf("I am also never run\n");
-} else {
-  printf("I print\n");
-}
-
-// While loops exist
-int ii = 0;
-while (ii < 10) {
-    printf("%d, ", ii++); // ii++ increments ii in-place, after using its value.
-} // => prints "0, 1, 2, 3, 4, 5, 6, 7, 8, 9, "
-
-printf("\n");
-
-int kk = 0;
-do {
-    printf("%d, ", kk);
-} while (++kk < 10); // ++kk increments kk in-place, before using its value
-// => prints "0, 1, 2, 3, 4, 5, 6, 7, 8, 9, "
-
-printf("\n");
-
-// For loops too
-int jj;
-for (jj=0; jj < 10; jj++) {
-    printf("%d, ", jj);
-} // => prints "0, 1, 2, 3, 4, 5, 6, 7, 8, 9, "
-
-printf("\n");
-
-///////////////////////////////////////
-// Typecasting
-///////////////////////////////////////
-
-// Every value in C has a type, but you can cast one value into another type
-// if you want.
-
-int x_hex = 0x01; // You can assign vars with hex literals
-
-// Casting between types will attempt to preserve their numeric values
-printf("%d\n", x_hex); // => Prints 1
-printf("%d\n", (short) x_hex); // => Prints 1
-printf("%d\n", (char) x_hex); // => Prints 1
-
-// Types will overflow without warning
-printf("%d\n", (char) 257); // => 1 (Max char = 255)
-
-// Integral types can be cast to floating-point types, and vice-versa.
-printf("%f\n", (float)100); // %f formats a float
-printf("%lf\n", (double)100); // %lf formats a double
-printf("%d\n", (char)100.0);
-
-///////////////////////////////////////
-// Pointers
-///////////////////////////////////////
-
-// A pointer is a variable declared to store a memory address. Its declaration will
-// also tell you the type of data it points to. You can retrieve the memory address 
-// of your variables, then mess with them.
-
-int x = 0;
-printf("%p\n", &x); // Use & to retrieve the address of a variable
-// (%p formats a pointer)
-// => Prints some address in memory;
-
-
-// Pointers start with * in their declaration
-int *px, not_a_pointer; // px is a pointer to an int
-px = &x; // Stores the address of x in px
-printf("%p\n", px); // => Prints some address in memory
-printf("%d, %d\n", (int)sizeof(px), (int)sizeof(not_a_pointer));
-// => Prints "8, 4" on 64-bit system
-
-// To retreive the value at the address a pointer is pointing to,
-// put * in front to de-reference it.
-printf("%d\n", *px); // => Prints 0, the value of x, which is what px is pointing to the address of
-
-// You can also change the value the pointer is pointing to.
-// We'll have to wrap the de-reference in parenthesis because
-// ++ has a higher precedence than *.
-(*px)++; // Increment the value px is pointing to by 1
-printf("%d\n", *px); // => Prints 1
-printf("%d\n", x); // => Prints 1
-
-int x_array[20]; // Arrays are a good way to allocate a contiguous block of memory
-int xx;
-for (xx=0; xx<20; xx++) {
-    x_array[xx] = 20 - xx;
-} // Initialize x_array to 20, 19, 18,... 2, 1
-
-// Declare a pointer of type int and initialize it to point to x_array
-int* x_ptr = x_array;
-// x_ptr now points to the first element in the array (the integer 20). 
-// This works because arrays are actually just pointers to their first element.
-
-// Arrays are pointers to their first element
-printf("%d\n", *(x_ptr)); // => Prints 20
-printf("%d\n", x_array[0]); // => Prints 20
-
-// Pointers are incremented and decremented based on their type
-printf("%d\n", *(x_ptr + 1)); // => Prints 19
-printf("%d\n", x_array[1]); // => Prints 19
-
-// You can also dynamically allocate contiguous blocks of memory with the
-// standard library function malloc, which takes one integer argument 
-// representing the number of bytes to allocate from the heap.
-int* my_ptr = (int*) malloc(sizeof(int) * 20);
-for (xx=0; xx<20; xx++) {
-    *(my_ptr + xx) = 20 - xx; // my_ptr[xx] = 20-xx would also work here
-} // Initialize memory to 20, 19, 18, 17... 2, 1 (as ints)
-
-// Dereferencing memory that you haven't allocated gives
-// unpredictable results
-printf("%d\n", *(my_ptr + 21)); // => Prints who-knows-what?
-
-// When you're done with a malloc'd block of memory, you need to free it, 
-// or else no one else can use it until your program terminates
-free(my_ptr);
-
-// Strings can be char arrays, but are usually represented as char
-// pointers:
-char* my_str = "This is my very own string";
-
-printf("%c\n", *my_str); // => 'T'
-
-function_1();
+    // print output using printf, for "print formatted"
+    // %d is an integer, \n is a newline
+    printf("%d\n", 0); // => Prints 0
+    // All statements must end with a semicolon
+    
+    ///////////////////////////////////////
+    // Types
+    ///////////////////////////////////////
+    
+    // You have to declare variables before using them. A variable declaration
+    // requires you to specify its type; a variable's type determines its size
+    // in bytes.
+    
+    // ints are usually 4 bytes 
+    int x_int = 0;
+    
+    // shorts are usually 2 bytes
+    short x_short = 0;
+    
+    // chars are guaranteed to be 1 byte
+    char x_char = 0;
+    char y_char = 'y'; // Char literals are quoted with ''
+    
+    // longs are often 4 to 8 bytes; long longs are guaranteed to be at least
+    // 64 bits
+    long x_long = 0;
+    long long x_long_long = 0; 
+    
+    // floats are usually 32-bit floating point numbers
+    float x_float = 0.0;
+    
+    // doubles are usually 64-bit floating-point numbers
+    double x_double = 0.0;
+    
+    // Integral types may be unsigned. This means they can't be negative, but
+    // the maximum value of an unsigned variable is greater than the maximum
+    // signed value of the same size.
+    unsigned char ux_char;
+    unsigned short ux_short;
+    unsigned int ux_int;
+    unsigned long long ux_long_long;
+    
+    // Other than char, which is always 1 byte (but not necessarily 8 bits!),
+    // these types vary in size depending on your machine and compiler.
+    // sizeof(T) gives you the size of a variable with type T in 
+    // bytes so you can express the size of these types in a portable way.
+    // sizeof(obj) yields the size of an actual expression (variable, literal, etc.).
+    // For example,
+    printf("%zu\n", sizeof(int)); // => 4 (on most machines with 4-byte words)
+    
+    
+    // It's worth noting that if the argument of the `sizeof` operator is not a type but an expression,
+    // then its argument is not evaluated except VLAs (see below). Also, `sizeof()` is an operator, not a function,
+    // furthermore, the value it yields is a compile-time constant (except when used on VLAs, again.)
+    int a = 1;
+    size_t size = sizeof(a++); // a++ is not evaluated
+    printf("sizeof(a++) = %zu where a = %d\n", size, a);
+    // the above code prints "sizeof(a++) = 4 where a = 1" (on a usual 32-bit architecture)
+    
+    // Arrays must be initialized with a concrete size.
+    char my_char_array[20]; // This array occupies 1 * 20 = 20 bytes
+    int my_int_array[20]; // This array occupies 4 * 20 = 80 bytes
+                          // (assuming 4-byte words)
+    
+    
+    // You can initialize an array to 0 thusly:
+    char my_array[20] = {0};
+    
+    // Indexing an array is like other languages -- or,
+    // rather, other languages are like C
+    my_array[0]; // => 0
+    
+    // Arrays are mutable; it's just memory!
+    my_array[1] = 2;
+    printf("%d\n", my_array[1]); // => 2
+    
+    // In C99 (and as an optional feature in C11), variable-length arrays (VLAs) can be declared as well.
+    // The size of such an array need not be a compile time constant:
+    printf("Enter the array size: "); // ask the user for an array size
+    char buf[0x100];
+    fgets(buf, sizeof buf, stdin);
+    size_t size = strtoul(buf, NULL, 10); // strtoul parses a string to an unsigned integer
+    int var_length_array[size]; // declare the VLA
+    printf("sizeof array = %zu\n", sizeof var_length_array);
+    
+    // A possible outcome of this program may be:
+    Enter the array size: 10
+    sizeof array = 40
+    
+    // Strings are just arrays of chars terminated by a NUL (0x00) byte,
+    // represented in strings as the special character '\0'.
+    // (We don't have to include the NUL byte in string literals; the compiler
+    //  inserts it at the end of the array for us.)
+    char a_string[20] = "This is a string";
+    printf("%s\n", a_string); // %s formats a string
+    
+    /*
+     You may have noticed that a_string is only 16 chars long.
+     Char #17 is the NUL byte. 
+     Chars #18, 19 and 20 are 0 as well - if an initializer list (in this case, the string literal)
+     has less elements than the array it is initializing, then excess array elements are implicitly
+     initialized to zero. This is why int ar[10] = { 0 } works as expected intuitively.
+    */
+    
+    printf("%d\n", a_string[16]); // => 0
+    
+    // So string literals are strings enclosed within double quotes, but if we have characters
+    // between single quotes, that's a character literal.
+    // It's of type `int`, and *not* `char` (for historical reasons).
+    int cha = 'a'; // fine
+    char chb = 'a'; // fine too (implicit conversion from int to char - truncation)
+    
+    ///////////////////////////////////////
+    // Operators
+    ///////////////////////////////////////
+    
+    int i1 = 1, i2 = 2; // Shorthand for multiple declaration
+    float f1 = 1.0, f2 = 2.0;
+    
+    // Arithmetic is straightforward
+    i1 + i2; // => 3
+    i2 - i1; // => 1
+    i2 * i1; // => 2
+    i1 / i2; // => 0 (0.5, but truncated towards 0)
+    
+    f1 / f2; // => 0.5, plus or minus epsilon - floating-point numbers and calculations are not exact
+    
+    // Modulo is there as well
+    11 % 3; // => 2
+    
+    // Comparison operators are probably familiar, but
+    // there is no boolean type in c. We use ints instead.
+    // (Or _Bool or bool in C99.)
+    // 0 is false, anything else is true. (The comparison 
+    // operators always yield 0 or 1.)
+    3 == 2; // => 0 (false)
+    3 != 2; // => 1 (true)
+    3 > 2; // => 1
+    3 < 2; // => 0
+    2 <= 2; // => 1
+    2 >= 2; // => 1
+    
+    // C is not Python - comparisons don't chain.
+    int a = 1;
+    // WRONG:
+    int between_0_and_2 = 0 < a < 2;
+    // Correct:
+    int between_0_and_2 = 0 < a && a < 2;
+    
+    // Logic works on ints
+    !3; // => 0 (Logical not)
+    !0; // => 1
+    1 && 1; // => 1 (Logical and)
+    0 && 1; // => 0
+    0 || 1; // => 1 (Logical or)
+    0 || 0; // => 0
+    
+    // Bitwise operators!
+    ~0x0F; // => 0xF0 (bitwise negation, "1's complement")
+    0x0F & 0xF0; // => 0x00 (bitwise AND)
+    0x0F | 0xF0; // => 0xFF (bitwise OR)
+    0x04 ^ 0x0F; // => 0x0B (bitwise XOR)
+    0x01 << 1; // => 0x02 (bitwise left shift (by 1))
+    0x02 >> 1; // => 0x01 (bitwise right shift (by 1))
+    
+    // Be careful when shifting signed integers - the following are all undefined behavior:
+    // - shifting into the sign bit of a signed integer (int a = 1 << 32)
+    // - left-shifting a negative number (int a = -1 << 2)
+    // - shifting by an offset which is more than or equal to the width of the type of the LHS:
+    //   int a = 1 << 32; // UB if int is 32 bits wide
+    
+    ///////////////////////////////////////
+    // Control Structures
+    ///////////////////////////////////////
+    
+    if (0) {
+      printf("I am never run\n");
+    } else if (0) {
+      printf("I am also never run\n");
+    } else {
+      printf("I print\n");
+    }
+    
+    // While loops exist
+    int ii = 0;
+    while (ii < 10) {
+        printf("%d, ", ii++); // ii++ increments ii in-place, after yielding its value ("postincrement").
+    } // => prints "0, 1, 2, 3, 4, 5, 6, 7, 8, 9, "
+    
+    printf("\n");
+    
+    int kk = 0;
+    do {
+        printf("%d, ", kk);
+    } while (++kk < 10); // ++kk increments kk in-place, and yields the already incremented value ("preincrement")
+    // => prints "0, 1, 2, 3, 4, 5, 6, 7, 8, 9, "
+    
+    printf("\n");
+    
+    // For loops too
+    int jj;
+    for (jj=0; jj < 10; jj++) {
+        printf("%d, ", jj);
+    } // => prints "0, 1, 2, 3, 4, 5, 6, 7, 8, 9, "
+    
+    printf("\n");
+    
+    // branching with multiple choices: switch()
+    switch (some_integral_expression) {
+    case 0: // labels need to be integral *constant* epxressions
+        do_stuff();
+        break; // if you don't break, control flow falls over labels - you usually don't want that.
+    case 1:
+        do_something_else();
+        break;
+    default:
+        // if `some_integral_expression` didn't match any of the labels
+        fputs("error!\n", stderr);
+        exit(-1);
+        break;
+    }
+        
+    
+    ///////////////////////////////////////
+    // Typecasting
+    ///////////////////////////////////////
+    
+    // Every value in C has a type, but you can cast one value into another type
+    // if you want (with some constraints).
+    
+    int x_hex = 0x01; // You can assign vars with hex literals
+    
+    // Casting between types will attempt to preserve their numeric values
+    printf("%d\n", x_hex); // => Prints 1
+    printf("%d\n", (short) x_hex); // => Prints 1
+    printf("%d\n", (char) x_hex); // => Prints 1
+    
+    // Types will overflow without warning
+    printf("%d\n", (unsigned char) 257); // => 1 (Max char = 255 if char is 8 bits long)
+    // printf("%d\n", (unsigned char) 257); would be undefined behavior - `char' is usually signed
+    // on most modern systems, and signed integer overflow invokes UB.
+    // Also, for determining the maximal value of a `char`, a `signed char` and an `unisigned char`,
+    // respectively, use the CHAR_MAX, SCHAR_MAX and UCHAR_MAX macros from <limits.h>
+    
+    // Integral types can be cast to floating-point types, and vice-versa.
+    printf("%f\n", (float)100); // %f formats a float
+    printf("%lf\n", (double)100); // %lf formats a double
+    printf("%d\n", (char)100.0);
+    
+    ///////////////////////////////////////
+    // Pointers
+    ///////////////////////////////////////
+    
+    // A pointer is a variable declared to store a memory address. Its declaration will
+    // also tell you the type of data it points to. You can retrieve the memory address 
+    // of your variables, then mess with them.
+    
+    int x = 0;
+    printf("%p\n", (void *)&x); // Use & to retrieve the address of a variable
+    // (%p formats an object pointer of type void *)
+    // => Prints some address in memory;
+    
+    
+    // Pointers start with * in their declaration
+    int *px, not_a_pointer; // px is a pointer to an int
+    px = &x; // Stores the address of x in px
+    printf("%p\n", (void *)px); // => Prints some address in memory
+    printf("%zu, %zu\n", sizeof(px), sizeof(not_a_pointer));
+    // => Prints "8, 4" on a typical 64-bit system
+    
+    // To retreive the value at the address a pointer is pointing to,
+    // put * in front to de-reference it.
+    // Note: yes, it may be confusing that '*' is used for _both_ declaring a pointer and dereferencing it.
+    printf("%d\n", *px); // => Prints 0, the value of x, which is what px is pointing to the address of
+    
+    // You can also change the value the pointer is pointing to.
+    // We'll have to wrap the de-reference in parenthesis because
+    // ++ has a higher precedence than *.
+    (*px)++; // Increment the value px is pointing to by 1
+    printf("%d\n", *px); // => Prints 1
+    printf("%d\n", x); // => Prints 1
+    
+    int x_array[20]; // Arrays are a good way to allocate a contiguous block of memory
+    int xx;
+    for (xx = 0; xx < 20; xx++) {
+        x_array[xx] = 20 - xx;
+    } // Initialize x_array to 20, 19, 18,... 2, 1
+    
+    // Declare a pointer of type int and initialize it to point to x_array
+    int* x_ptr = x_array;
+    // x_ptr now points to the first element in the array (the integer 20). 
+    // This works because arrays often decay into pointers to their first element.
+    // For example, when an array is passed to a function or is assigned to a pointer,
+    // it decays into (implicitly converted to) a pointer.
+    // Exceptions: when the array is the argument of the `&` (address-od) operator:
+    int arr[10];
+    int (*ptr_to_arr)[10] = &arr; // &arr is NOT of type `int *`! It's of type "pointer to array" (of ten `int`s).
+    // or when the array is a string literal used for initializing a char array:
+    char arr[] = "foobarbazquirk";
+    // or when it's the argument of the `sizeof` or `alignof` operator:
+    int arr[10];
+    int *ptr = arr; // equivalent with int *ptr = &arr[0];
+    printf("%zu %zu\n", sizeof arr, sizeof ptr); // probably prints "40, 4" or "40, 8"
+    
+
+    // Pointers are incremented and decremented based on their type
+    // (this is called pointer arithmetic)
+    printf("%d\n", *(x_ptr + 1)); // => Prints 19
+    printf("%d\n", x_array[1]); // => Prints 19
+    
+    // You can also dynamically allocate contiguous blocks of memory with the
+    // standard library function malloc, which takes one argument of type size_t
+    // representing the number of bytes to allocate (usually from the heap, although this
+    // may not be true on e. g. embedded systems - the C standard says nothing about it).
+    int *my_ptr = malloc(sizeof(*my_ptr) * 20);
+    for (xx = 0; xx < 20; xx++) {
+        *(my_ptr + xx) = 20 - xx; // my_ptr[xx] = 20-xx would also work here, and it's also more readable
+    } // Initialize memory to 20, 19, 18, 17... 2, 1 (as ints)
+    
+    // Dereferencing memory that you haven't allocated gives
+    // "unpredictable results" - the program is said to invoke "undefined behavior"
+    printf("%d\n", *(my_ptr + 21)); // => Prints who-knows-what? It may even crash.
+    
+    // When you're done with a malloc'd block of memory, you need to free it, 
+    // or else no one else can use it until your program terminates
+    // (this is called a "memory leak"):
+    free(my_ptr);
+    
+    // Strings are arrays of char, but they are usually represented as a
+    // pointer-to-char (which is a pointer to the first element of the array).
+    // It's good practice to use `const char *' when referring to a string literal,
+    // since string literals shall not be modified (i. e. "foo"[0] = 'a' is ILLEGAL.)
+    const char *my_str = "This is my very own string literal";
+    printf("%c\n", *my_str); // => 'T'
+    
+    // This is not the case if the string is an array (potentially initialized with a string literal)
+    // that resides in writable memory, as in:
+    char foo[] = "foo";
+    foo[0] = 'a'; // this is legal, foo now contains "aoo"
+    
+    function_1();
 } // end main function
 
 ///////////////////////////////////////
@@ -300,7 +396,8 @@ function_1();
 // Function declaration syntax:
 // <return type> <function name>(<args>)
 
-int add_two_ints(int x1, int x2){
+int add_two_ints(int x1, int x2)
+{
     return x1 + x2; // Use return to return a value
 }
 
@@ -312,10 +409,12 @@ Example: in-place string reversal
 */
 
 // A void function returns no value
-void str_reverse(char* str_in){
+void str_reverse(char *str_in)
+{
     char tmp;
-    int ii=0, len = strlen(str_in); // Strlen is part of the c standard library
-    for(ii=0; ii<len/2; ii++){
+    int ii = 0;
+    size_t len = strlen(str_in); // `strlen()` is part of the c standard library
+    for (ii = 0; ii < len / 2; ii++) {
         tmp = str_in[ii];
         str_in[ii] = str_in[len - ii - 1]; // ii-th char from end
         str_in[len - ii - 1] = tmp;
@@ -336,15 +435,20 @@ printf("%s\n", c); // => ".tset a si sihT"
 typedef int my_type;
 my_type my_type_var = 0;
 
-// Structs are just collections of data
+// Structs are just collections of data, the members are allocated sequentially, in the order they are written:
 struct rectangle {
     int width;
     int height;
 };
 
+// it's generally not true that sizeof(struct rectangle) == sizeof(int) + sizeof(int) due to
+// potential padding between the structure members (this is for alignment reasons. Probably won't
+// happen if all members are of the same type, but watch out!
+// See http://stackoverflow.com/questions/119123/why-isnt-sizeof-for-a-struct-equal-to-the-sum-of-sizeof-of-each-member
+// for further information.
 
-void function_1(){
-
+void function_1()
+{
     struct rectangle my_rec;
 
     // Access struct members with .
@@ -352,22 +456,29 @@ void function_1(){
     my_rec.height = 20;
 
     // You can declare pointers to structs
-    struct rectangle* my_rec_ptr = &my_rec;
+    struct rectangle *my_rec_ptr = &my_rec;
 
     // Use dereferencing to set struct pointer members...
     (*my_rec_ptr).width = 30;
 
-    // ... or use the -> shorthand
+    // ... or even better: prefer the -> shorthand for the sake of readability
     my_rec_ptr->height = 10; // Same as (*my_rec_ptr).height = 10;
 }
 
 // You can apply a typedef to a struct for convenience
 typedef struct rectangle rect;
 
-int area(rect r){
+int area(rect r)
+{
     return r.width * r.height;
 }
 
+// if you have large structs, you can pass them "by pointer" to avoid copying the whole struct:
+int area(const rect *r)
+{
+    return r->width * r->height;
+}
+
 ///////////////////////////////////////
 // Function pointers 
 ///////////////////////////////////////
@@ -379,10 +490,11 @@ However, definition syntax may be initially confusing.
 
 Example: use str_reverse from a pointer
 */
-void str_reverse_through_pointer(char * str_in) {
+void str_reverse_through_pointer(char *str_in) {
     // Define a function pointer variable, named f. 
     void (*f)(char *); // Signature should exactly match the target function.
     f = &str_reverse; // Assign the address for the actual function (determined at runtime)
+    // f = str_reverse; would work as well - functions decay into pointers, similar to arrays
     (*f)(str_in); // Just calling the function through the pointer
     // f(str_in); // That's an alternative but equally valid syntax for calling it.
 }
@@ -403,7 +515,15 @@ typedef void (*my_fnp_type)(char *);
 ## Further Reading
 
 Best to find yourself a copy of [K&R, aka "The C Programming Language"](https://en.wikipedia.org/wiki/The_C_Programming_Language)
+It is *the* book about C, written by the creators of C. Be careful, though - it's ancient and it contains some
+inaccuracies (well, ideas that are not considered good anymore) or now-changed practices.
+
+Another good resource is [Learn C the hard way](http://c.learncodethehardway.org/book/).
+
+If you have a question, read the [compl.lang.c Frequently Asked Questions](http://c-faq.com).
 
-Another good resource is [Learn C the hard way](http://c.learncodethehardway.org/book/)
+It's very important to use proper spacing, indentation and to be consistent with your coding style in general.
+Readable code is better than clever code and fast code. For a good, sane coding style to adopt, see the
+[Linux kernel coding stlye](https://www.kernel.org/doc/Documentation/CodingStyle).
 
 Other than that, Google is your friend.