diff options
| -rw-r--r-- | c.html.markdown | 32 | ||||
| -rw-r--r-- | clojure.html.markdown | 3 | ||||
| -rw-r--r-- | python.html.markdown | 16 |
3 files changed, 38 insertions, 13 deletions
diff --git a/c.html.markdown b/c.html.markdown index 15bfa05e..c23e8d2c 100644 --- a/c.html.markdown +++ b/c.html.markdown @@ -50,8 +50,8 @@ short x_short = 0; 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 +long x_long = 0; // Still 32 bits for historical reasons +long long x_long_long = 0; // Guaranteed to be at least 64 bits // 32-bit floating-point decimal float x_float = 0.0; @@ -194,26 +194,42 @@ printf("%d\n", (short) 65537); // => 1 (Max short = 65535) // Pointers /////////////////////////////////////// -// You can retrieve the memory address of your variables, -// then mess with them. +// 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; +// Pointer types end with * in their declaration +int* px; // 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 + +// 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 -// Pointer types end with * +// Declare a pointer of type int and initialize it to point to x_array int* x_ptr = x_array; -// This works because arrays are pointers to their first element. +// This works because an array name is bound to the address of its 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. +// Arrays are pointers to their first element printf("%d\n", *(x_ptr)); // => Prints 20 printf("%d\n", x_array[0]); // => Prints 20 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/python.html.markdown b/python.html.markdown index a599f5d3..4cfecbbd 100644 --- a/python.html.markdown +++ b/python.html.markdown @@ -8,6 +8,8 @@ Python was created by Guido Van Rossum in the early 90's. It is now one of the m languages in existence. I fell in love with Python for it's syntactic clarity. It's basically executable pseudocode. +Feedback would be highly appreciated! You can reach me at [@louiedinh](http://twitter.com/louiedinh) or louiedinh [at] [google's email service] + Note: This article applies to Python 2.7 specifically, but should be applicable to Python 2.x. Look for another tour of Python 3 soon! @@ -32,11 +34,11 @@ to Python 2.x. Look for another tour of Python 3 soon! # Division is a bit tricky. It is integer division and floors the results # automatically. -11 / 4 #=> 2 +5 / 2 #=> 2 # To fix division we need to learn about floats. 2.0 # This is a float -5.0 / 2.0 #=> 2.5 ahhh...much better +11.0 / 4.0 #=> 2.75 ahhh...much better # Enforce precedence with parentheses (1 + 3) * 2 #=> 8 @@ -134,9 +136,9 @@ except IndexError: # (It's a closed/open range for you mathy types.) li[1:3] #=> [2, 4] # Omit the beginning -li[:3] #=> [1, 2, 4] -# Omit the end li[2:] #=> [4, 3] +# Omit the end +li[:3] #=> [1, 2, 4] # Remove arbitrary elements from a list with del del li[2] # li is now [1, 2, 3] @@ -167,7 +169,7 @@ tup + (4, 5, 6) #=> (1, 2, 3, 4, 5, 6) tup[:2] #=> (1, 2) 2 in tup #=> True -# However, you can unpack tuples into variables +# You can unpack tuples into variables 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 @@ -407,3 +409,7 @@ j.get_species() #=> "H. neanderthalensis" Human.grunt() #=> "*grunt*" ``` +## Further Reading + +Still up for more? Try [Learn Python The Hard Way](http://learnpythonthehardway.org/book/) + |