diff --git a/c.html.markdown b/c.html.markdown
index ff396d21..7405c7ab 100644
--- a/c.html.markdown
+++ b/c.html.markdown
@@ -46,31 +46,47 @@ Multi-line comments don't nest /* Be careful */ // comment ends on this line...
// Enumeration constants are also ways to declare constants.
// All statements must end with a semicolon
-enum days {SUN = 1, MON, TUE, WED, THU, FRI, SAT};
+enum days {SUN, MON, TUE, WED, THU, FRI, SAT};
+// SUN gets 0, MON gets 1, TUE gets 2, etc.
+
+// Enumeration values can also be specified
+enum days {SUN = 1, MON, TUE, WED = 99, THU, FRI, SAT};
// MON gets 2 automatically, TUE gets 3, etc.
+// WED get 99, THU gets 100, FRI gets 101, etc.
// Import headers with #include
#include
#include
#include
-// (File names between are headers from the C standard library.)
-// For your own headers, use double quotes instead of angle brackets:
-//#include "my_header.h"
+// File names between tell the compiler to look in your system
+// libraries for the headers.
+// For your own headers, use double quotes instead of angle brackets, and
+// provide the path:
+#include "my_header.h" // local file
+#include "../my_lib/my_lib_header.h" //relative path
// Declare function signatures in advance in a .h file, or at the top of
// your .c file.
void function_1();
int function_2(void);
-// Must declare a 'function prototype' before main() when functions occur after
-// your main() function.
+// At a minimum, you must declare a 'function prototype' before its use in any function.
+// Normally, prototypes are placed at the top of a file before any function definition.
int add_two_ints(int x1, int x2); // function prototype
// although `int add_two_ints(int, int);` is also valid (no need to name the args),
// it is recommended to name arguments in the prototype as well for easier inspection
-// Your program's entry point is a function called
-// main with an integer return type.
+// Function prototypes are not necessary if the function definition comes before
+// any other function that calls that function. However, it's standard practice to
+// always add the function prototype to a header file (*.h) and then #include that
+// file at the top. This prevents any issues where a function might be called
+// before the compiler knows of its existence, while also giving the developer a
+// clean header file to share with the rest of the project.
+
+// Your program's entry point is a function called "main". The return type can
+// be anything, however most operating systems expect a return type of `int` for
+// error code processing.
int main(void) {
// your program
}
@@ -96,13 +112,14 @@ int main (int argc, char** argv)
// For the sake of the tutorial, variables are declared dynamically under
// C99-compliant standards.
- // ints are usually 4 bytes
+ // ints are usually 4 bytes (use the `sizeof` operator to check)
int x_int = 0;
- // shorts are usually 2 bytes
+ // shorts are usually 2 bytes (use the `sizeof` operator to check)
short x_short = 0;
- // chars are guaranteed to be 1 byte
+ // chars are defined as the smallest addressable unit for a processor.
+ // This is usually 1 byte, but for some systems it can be more (ex. for TMS320 from TI it's 2 bytes).
char x_char = 0;
char y_char = 'y'; // Char literals are quoted with ''
@@ -225,13 +242,22 @@ int main (int argc, char** argv)
i1 / (double)i2; // => 0.5 // Same with double
f1 / f2; // => 0.5, plus or minus epsilon
- // Floating-point numbers and calculations are not exact
- // for instance it is not giving mathematically correct results
+ // Floating-point numbers are defined by IEEE 754, thus cannot store perfectly
+ // exact values. For instance, the following does not produce expected results
+ // because 0.1 might actually be 0.099999999999 insided the computer, and 0.3
+ // might be stored as 0.300000000001.
(0.1 + 0.1 + 0.1) != 0.3; // => 1 (true)
- // and it is NOT associative
+ // and it is NOT associative due to reasons mentioned above.
1 + (1e123 - 1e123) != (1 + 1e123) - 1e123; // => 1 (true)
// this notation is scientific notations for numbers: 1e123 = 1*10^123
+ // It is important to note that most all systems have used IEEE 754 to
+ // represent floating points. Even python, used for scientific computing,
+ // eventually calls C which uses IEEE 754. It is mentioned this way not to
+ // indicate that this is a poor implementation, but instead as a warning
+ // that when doing floating point comparisons, a little bit of error (epsilon)
+ // needs to be considered.
+
// Modulo is there as well, but be careful if arguments are negative
11 % 3; // => 2 as 11 = 2 + 3*x (x=3)
(-11) % 3; // => -2, as one would expect
@@ -239,7 +265,7 @@ int main (int argc, char** argv)
// Comparison operators are probably familiar, but
// there is no Boolean type in C. We use ints instead.
- // (Or _Bool or bool in C99.)
+ // (C99 introduced the _Bool type provided in stdbool.h)
// 0 is false, anything else is true. (The comparison
// operators always yield 0 or 1.)
3 == 2; // => 0 (false)
@@ -391,13 +417,16 @@ int main (int argc, char** argv)
// if you want (with some constraints).
int x_hex = 0x01; // You can assign vars with hex literals
+ // binary is not in the standard, but allowed by some
+ // compilers (x_bin = 0b0010010110)
// 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
+ // If you assign a value greater than a types max val, it will rollover
+ // without warning.
printf("%d\n", (unsigned char) 257); // => 1 (Max char = 255 if char is 8 bits long)
// For determining the max value of a `char`, a `signed char` and an `unsigned char`,
@@ -588,6 +617,24 @@ printf("first: %d\nsecond: %d\n", first, second);
// values will be swapped
*/
+// Return multiple values.
+// C does not allow for returning multiple values with the return statement. If
+// you would like to return multiple values, then the caller must pass in the
+// variables where they would like the returned values to go. These variables must
+// be passed in as pointers such that the function can modify them.
+int return_multiple( int *array_of_3, int *ret1, int *ret2, int *ret3)
+{
+ if(array_of_3 == NULL)
+ return 0; //return error code (false)
+
+ //de-reference the pointer so we modify its value
+ *ret1 = array_of_3[0];
+ *ret2 = array_of_3[1];
+ *ret3 = array_of_3[2];
+
+ return 1; //return error code (true)
+}
+
/*
With regards to arrays, they will always be passed to functions
as pointers. Even if you statically allocate an array like `arr[10]`,
@@ -716,6 +763,10 @@ typedef void (*my_fnp_type)(char *);
// my_fnp_type f;
+/////////////////////////////
+// Printing characters with printf()
+/////////////////////////////
+
//Special characters:
/*
'\a'; // alert (bell) character