diff options
| -rw-r--r-- | c.html.markdown | 338 | ||||
| -rw-r--r-- | clojure.html.markdown | 3 | ||||
| -rw-r--r-- | php.html.markdown | 86 | ||||
| -rw-r--r-- | python.html.markdown | 104 |
4 files changed, 487 insertions, 44 deletions
diff --git a/c.html.markdown b/c.html.markdown new file mode 100644 index 00000000..15bfa05e --- /dev/null +++ b/c.html.markdown @@ -0,0 +1,338 @@ +--- +language: c +author: Adam Bard +author_url: http://adambard.com/ +--- + +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 // +/* +Multi-line comments look like this. +*/ + +// Import headers with #include +#include <stdlib.h> +#include <stdio.h> + +// Declare function signatures in advance in a .h file, or at the top of +// your .c file. +void function_1(); +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 +/////////////////////////////////////// + +// Variables must always be declared with a type. + +// 32-bit integer +int x_int = 0; + +// 16-bit integer +short x_short = 0; + +// 8-bit integer, aka 1 byte +char x_char = 0; +char y_char = 'y'; // Char literals are quoted with '' + +long x_long = 0; // Still 32 bytes for historical reasons +long long x_long_long = 0; // Guaranteed to be at least 64 bytes + +// 32-bit floating-point decimal +float x_float = 0.0; + +// 64-bit floating-point decimal +double x_double = 0.0; + +// Integer types may be unsigned +unsigned char ux_char; +unsigned short ux_short; +unsigned int ux_int; +unsigned long long ux_long_long; + +// 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 + + +// 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 lists of chars terminated by a null (0x00) byte. +char a_string[20] = "This is a string"; + +/* +You may have noticed that a_string is only 16 chars long. +Char #17 is a null byte, 0x00 aka \0. +Chars #18, 19 and 20 have undefined values. +*/ + +printf("%d\n", a_string[16]); + +/////////////////////////////////////// +// 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 +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 +/////////////////////////////////////// + +// Everything in C is stored somewhere in memory. You can change +// the type of a variable to choose how to read its data + +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) +printf("%d\n", (short) 65537); // => 1 (Max short = 65535) + +/////////////////////////////////////// +// Pointers +/////////////////////////////////////// + +// 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; + +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 + +// Pointer types end with * +int* x_ptr = x_array; +// This works because arrays are pointers to their first element. + +// Put a * in front to de-reference a pointer and retrieve the value, +// of the same type as the pointer, that the pointer is pointing at. +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 + +// Array indexes are such a thin wrapper around pointer +// arithmetic that the following works: +printf("%d\n", 0[x_array]); // => Prints 20; +printf("%d\n", 2[x_array]); // => Prints 18; + +// The above is equivalent to: +printf("%d\n", *(0 + x_ptr)); +printf("%d\n", *(2 + x_ptr)); + +// You can give a pointer a block of memory to use with malloc +int* my_ptr = (int*) malloc(sizeof(int) * 20); +for(xx=0; xx<20; xx++){ + *(my_ptr + xx) = 20 - xx; +} // 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, you need to free it +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("%d\n", *my_str); // 84 (The ascii value of 'T') + +function_1(); +} // end main function + +/////////////////////////////////////// +// Functions +/////////////////////////////////////// + +// Function declaration syntax: +// <return type> <function name>(<args>) + +int add_two_ints(int x1, int x2){ + return x1 + x2; // Use return a return a value +} + +/* +Pointers are passed-by-reference (duh), so functions +can mutate their values. + +Example: in-place string reversal +*/ + +// A void function returns no value +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++){ + tmp = str_in[ii]; + str_in[ii] = str_in[len - ii - 1]; // ii-th char from end + str_in[len - ii - 1] = tmp; + } +} + +/* +char c[] = "This is a test."; +str_reverse(c); +printf("%s\n", c); // => ".tset a si sihT" +*/ + +/////////////////////////////////////// +// User-defined types and structs +/////////////////////////////////////// + +// Typedefs can be used to create type aliases +typedef int my_type; +my_type my_type_var = 0; + +// Structs are just collections of data +struct rectangle { + int width; + int height; +}; + + +void function_1(){ + + struct rectangle my_rec; + + // Access struct members with . + my_rec.width = 10; + my_rec.height = 20; + + // You can declare pointers to structs + struct rectangle* my_rec_ptr = &my_rec; + + // Use dereferencing to set struct pointer members... + (*my_rec_ptr).width = 30; + + // ... or use the -> shorthand + 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){ + return r.width * r.height; +} + +``` + +## 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) + +Another good resource is [Learn C the hard way](http://c.learncodethehardway.org/book/) + +Other than that, Google is your friend. diff --git a/clojure.html.markdown b/clojure.html.markdown index 5086d2c2..24250a87 100644 --- a/clojure.html.markdown +++ b/clojure.html.markdown @@ -12,6 +12,9 @@ state as it comes up. This combination allows it to handle concurrent processing very simply, and often automatically. +(You need a version of Clojure 1.2 or newer) + + ```clojure ; Comments start with semicolons. diff --git a/php.html.markdown b/php.html.markdown index cddba644..753f6ab1 100644 --- a/php.html.markdown +++ b/php.html.markdown @@ -47,8 +47,8 @@ $integer = 0123; // octal number (equivalent to 83 decimal) $integer = 0x1A; // hexadecimal number (equivalent to 26 decimal) // Floats (aka doubles) -$float = 1.234; -$float = 1.2e3; +$float = 1.234; +$float = 1.2e3; $float = 7E-10; // Arithmetic @@ -87,7 +87,7 @@ $sgl_quotes END; // Nowdoc syntax is available in PHP 5.3.0 // Manipulation -$concatenated = $sgl_quotes + $dbl_quotes; +$concatenated = $sgl_quotes . $dbl_quotes; ``` ### Compound @@ -119,6 +119,8 @@ print('Hello World!'); // The same as echo // echo is actually a language construct, so you can drop the parentheses. echo 'Hello World!'; +print 'Hello World!'; // So is print + echo 100; echo $variable; echo function_result(); @@ -135,12 +137,12 @@ echo function_result(); ```php <?php -$a = 1; -$b = 2; -$a = $b; // A now contains the same value sa $b -$a =& $b; -// A now contains a reference to $b. Changing the value of -// $a will change the value of $b also, and vice-versa. +$x = 1; +$y = 2; +$x = $y; // A now contains the same value sa $y +$x = &$y; +// $x now contains a reference to $y. Changing the value of +// $x will change the value of $y also, and vice-versa. ``` ### Comparison @@ -148,15 +150,20 @@ $a =& $b; ```php <?php +// These comparisons will always be true, even if the types aren't the same. $a == $b // TRUE if $a is equal to $b after type juggling. -$a === $b // TRUE if $a is equal to $b, and they are of the same type. $a != $b // TRUE if $a is not equal to $b after type juggling. $a <> $b // TRUE if $a is not equal to $b after type juggling. -$a !== $b // TRUE if $a is not equal to $b, or they are not of the same type. $a < $b // TRUE if $a is strictly less than $b. $a > $b // TRUE if $a is strictly greater than $b. $a <= $b // TRUE if $a is less than or equal to $b. $a >= $b // TRUE if $a is greater than or equal to $b. + +// The following will only be true if the values match and are the same type. +$a === $b // TRUE if $a is equal to $b, and they are of the same type. +$a !== $b // TRUE if $a is not equal to $b, or they are not of the same type. +1 == '1' // TRUE +1 === '1' // FALSE ``` ## [Type Juggling](http://www.php.net/manual/en/language.types.type-juggling.php) @@ -176,7 +183,11 @@ echo $string + $string; $string = 'one'; echo $string + $string; // Outputs 0 because the + operator cannot cast the string 'one' to a number +``` +Type casting can be used to treat a variable as another type temporarily by using cast operators in parentheses. + +```php $boolean = (boolean) $integer; // $boolean is true $zero = 0; @@ -222,9 +233,9 @@ if (/* test */) { ?> <?php if (/* test */): ?> -<!-- Do something that isn't PHP --> +This is displayed if the test is truthy. <?php else: ?> -<!-- Do something default --> +This is displayed otherwise. <?php endif; ?> ``` @@ -278,7 +289,6 @@ while ($i < 5) { if ($i == 3) { break; // Exit out of the while loop and continue. } - echo $i++; } @@ -288,7 +298,6 @@ while ($i < 5) { if ($i == 3) { continue; // Skip this iteration of the loop } - echo $i++; } ``` @@ -325,8 +334,8 @@ number of letters, numbers, or underscores. There are three ways to declare func ```php <?php -function my_function_name ($arg_1, $arg_2) { // $arg_1 and $arg_2 are required - // Do something with $arg_1 and $arg_2; +function my_function_name ($arg_1, $arg_2) { + // $arg_1 and $arg_2 are required } // Functions may be nested to limit scope @@ -335,7 +344,25 @@ function outer_function ($arg_1 = null) { // $arg_1 is optional } } -// inner_function() does not exist and cannot be called until outer_function() is called +// inner_function() does not exist and cannot be called until +// outer_function() is called +``` + +This enables [currying](http://en.wikipedia.org/wiki/Currying) in PHP. + +```php +function foo ($x, $y, $z) { + echo "$x - $y - $z"; +} + +function bar ($x, $y) { + return function ($z) use ($x, $y) { + foo($x, $y, $z); + }; +} + +$bar = bar('A', 'B'); +$bar('C'); ``` ### [Variable](http://www.php.net/manual/en/functions.variable-functions.php) @@ -355,7 +382,11 @@ Similar to variable functions, functions may be anonymous. ```php <?php -my_function(function () { +function my_function($callback) { + $callback('My argument'); +} + +my_function(function ($my_argument) { // do something }); @@ -395,13 +426,11 @@ methods if they belong to a class. class MyClass { function myFunction() { } - - function function youCannotOverrideMe() - { + + final function youCannotOverrideMe() { } - - public static function myStaticMethod() - { + + public static function myStaticMethod() { } } @@ -421,12 +450,12 @@ PHP offers some [magic methods](http://www.php.net/manual/en/language.oop5.magic class MyClass { private $property; - + public function __get($key) { return $this->$key; } - + public function __set($key, $value) { $this->$key = $value; @@ -438,7 +467,8 @@ echo $x->property; // Will use the __get() method $x->property = 'Something'; // Will use the __set() method ``` -Classes can be abstract (using the ```abstract``` keyword), extend other classes (using the ```extends``` keyword) and implement interfaces (using the ```implements``` keyword). An interface is declared with the ```interface``` keyword. +Classes can be abstract (using the ```abstract``` keyword), extend other classes (using the ```extends``` keyword) and +implement interfaces (using the ```implements``` keyword). An interface is declared with the ```interface``` keyword. ```php <?php diff --git a/python.html.markdown b/python.html.markdown index 32b7dc93..42c498b1 100644 --- a/python.html.markdown +++ b/python.html.markdown @@ -26,7 +26,7 @@ to Python 2.x. Look for another tour of Python 3 soon! # Math is what you would expect 1 + 1 #=> 2 -8 - 1 #=> 9 +8 - 1 #=> 7 10 * 2 #=> 20 35 / 5 #=> 7 @@ -49,11 +49,24 @@ False not True #=> False not False #=> True - # Equality is == 1 == 1 #=> True 2 == 1 #=> False +# Inequality is != +1 != 1 #=> False +2 != 1 #=> True + +# More comparisons +1 < 10 #=> True +1 > 10 #=> False +2 <= 2 #=> True +2 >= 2 #=> True + +# Comparisons can be chained ! +1 < 2 < 3 #=> True +2 < 3 < 2 #=> False + # Strings are created with " or ' "This is a string." 'This is also a string.' @@ -81,8 +94,15 @@ some_var = 5 # Convention is to use lower_case_with_underscores some_var #=> 5 # Accessing a previously unassigned variable is an exception -some_other_var # Will raise a NameError +try: + some_other_var +except NameError: + print "Raises a name error" +# Conditional Expressions can be used when assigning +some_var = a if a > b else b +# If a is greater than b, then a is assigned to some_var. +# Otherwise b is assigned to some_var. # Lists store sequences li = [] @@ -102,11 +122,16 @@ li.append(3) # li is now [1, 2, 4, 3] again. # Access a list like you would any array li[0] #=> 1 # Look at the last element -li[-1] #=> 4 +li[-1] #=> 3 + # Looking out of bounds is an IndexError -li[4] # Raises an IndexError +try: + li[4] # Raises an IndexError +except IndexError: + print "Raises an IndexError" -# You can look at ranges with slice syntax. It's an closed/open range for you mathy types. +# You can look at ranges with slice syntax. +# (It's a closed/open range for you mathy types.) li[1:3] #=> [2, 4] # Omit the beginning li[:3] #=> [1, 2, 4] @@ -120,7 +145,7 @@ del li[2] # li is now [1, 2, 3] li + other_li #=> [1, 2, 3, 4, 5, 6] - Note: li and other_li is left alone # Concatenate lists with extend -li.extend(other_li) # Now li is [1, 2, 3, 4, 5, 6] +li.extend(other_li) # Now li is [1, 2, 3, 4, 5, 6] # Check for existence in a list with in 1 in li #=> True @@ -131,7 +156,10 @@ len(li) #=> 6 # Tuples are like lists but are immutable. tup = (1, 2, 3) tup[0] #=> 1 -tup[0] = 3 # Raises a TypeError +try: + tup[0] = 3 # Raises a TypeError +except TypeError: + print "Tuples cannot be mutated." # You can do all those list thingies on tuples too len(tup) #=> 3 @@ -143,7 +171,7 @@ tup[:2] #=> (1, 2) a, b, c = (1, 2, 3) # a is now 1, b is now 2 and c is now 3 # Tuples are created by default if you leave out the parentheses d, e, f = 4, 5, 6 -# Now look how easy it is to swap to values +# Now look how easy it is to swap two values e, d = d, e # d is now 5 and e is now 4 @@ -168,6 +196,21 @@ filled_dict.values() #=> [3, 2, 1] "one" in filled_dict #=> True 1 in filled_dict #=> False +# Trying to look up a non-existing key will raise a KeyError +filled_dict["four"] #=> KeyError + +# Use get method to avoid the KeyError +filled_dict.get("one") #=> 1 +filled_dict.get("four") #=> None + +# The get method supports a default argument when the value is missing +filled_dict.get("one", 4) #=> 1 +filled_dict.get("four", 4) #=> 4 + +# Setdefault method is a safe way to add new key-value pair into dictionary +filled_dict.setdefault("five", 5) #filled_dict["five"] is set to 5 +filled_dict.setdefault("five", 6) #filled_dict["five"] is still 5 + # Sets store ... well sets empty_set = set() @@ -216,14 +259,14 @@ prints: """ for animal in ["dog", "cat", "mouse"]: # You can use % to interpolate formatted strings - print "%s is a mammal" % animal + print "%s is a mammal" % animal """ While loops go until a condition is no longer met. prints: 0 1 - 2 + 2 3 """ x = 0 @@ -232,11 +275,20 @@ while x < 4: x += 1 # Shorthand for x = x + 1 # Handle exceptions with a try/except block + +# Works on Python 2.6 and up: try: - raise IndexError("This is an index error") # Use raise to raise an error + # Use raise to raise an error + raise IndexError("This is an index error") except IndexError as e: pass # Pass is just a no-op. Usually you would do recovery here. +# Works for Python 2.7 and down: +try: + raise IndexError("This is an index error") +except IndexError, e: # No "as", comma instead + pass + #################################################### ## 4. Functions @@ -252,20 +304,38 @@ add(5, 6) #=> 11 and prints out "x is 5 and y is 6" # Another way to call functions is with keyword arguments add(y=6, x=5) # Keyword arguments can arrive in any order. -# You can define functions that take a variable number of positional arguments +# You can define functions that take a variable number of +# positional arguments def varargs(*args): return args varargs(1, 2, 3) #=> (1,2,3) -# You can define functions that take a variable number of keyword arguments +# You can define functions that take a variable number of +# keyword arguments, as well def keyword_args(**kwargs): return kwargs # Let's call it to see what happens keyword_args(big="foot", loch="ness") #=> {"big": "foot", "loch": "ness"} +# You can do both at once, if you like +def all_the_args(*args, **kwargs): + print args + print kwargs +""" +all_the_args(1, 2, a=3, b=4) prints: + [1, 2] + {"a": 3, "b": 4} +""" + +# You can also use * and ** when calling a function +args = (1, 2, 3, 4) +kwargs = {"a": 3, "b": 4} +foo(*args) # equivalent to foo(1, 2, 3, 4) +foo(**kwargs) # equivalent to foo(a=3, b=4) +foo(*args, **kwargs) # equivalent to foo(1, 2, 3, 4, a=3, b=4) # Python has first class functions def create_adder(x): @@ -273,7 +343,7 @@ def create_adder(x): return x + y return adder -add_10 = create_adder(10): +add_10 = create_adder(10) add_10(3) #=> 13 # There are also anonymous functions @@ -329,9 +399,11 @@ print j.say("hello") #prints out "Joel: hello" i.get_species() #=> "H. sapiens" # Change the shared attribute -i.species = "H. neanderthalensis" +Human.species = "H. neanderthalensis" i.get_species() #=> "H. neanderthalensis" j.get_species() #=> "H. neanderthalensis" # Call the static method Human.grunt() #=> "*grunt*" +``` + |