Machine Arithmetic Characters and Strings 1 25 2012 Opening Discussion Questions about the quiz ACM Meeting Minute essay comments Binary clocks Is Scala a program within a program Switching desktops Programming in the TV film industry What is the coolest thing I have ever coded Google e mails and spam Jobs understanding complex systems Manual Binary Conversion Going from binary to decimal is done by simply adding the values of the positions for the 1s We ll describe two methods of going from decimal to binary Repeated subtraction of largest power of 2 Repeated division by 2 This one is probably easiest Binary Addition Adding binary numbers is very easy Just do the long addition that you are used to You will carry a lot more frequently because anything above 1 causes a carry Let s run through some examples Consider implications of fixed precision Negative Numbers We don t have a in the computer for negative numbers All we have are 1 and 0 So how do we make negative numbers Remember the definition of negative numbers as additive inverse a a 0 We want to preserve this to keep addition simple This gives us 2s compliment numbers Binary Multiplication Multiplying binary numbers works just like long multiplication with decimals but easier My only recommendation is you only add two numbers at a time and take it in steps Hexadecimal Binary is unwieldy for humans because of the large number of digits Hexadecimal base 16 is commonly used because it converts nicely to binary but has few digits Four bits is a hex digit Start at the right and group bits by 4 Use letters A F for numbers 10 15 Hex literals start with 0x toHexString Octal Octal base 8 is less common than hex but not uncommon Group bits into groups of three Octal literals and toOctalString The math Object For other math functions use methods on the math object For example use math sqrt to take the square root of a number Characters The Char type represents a single character in Scala The literal for Char has the letter that you want in single quotes The Char is stored in the computer as a 16 bit unsigned integer encoded in Unicode Unicode has the alphabet of every written language in it You can convert to an Int to see the numeric values of characters Escape Characters Not all characters can be easily entered For things you can t nicely type use escape characters n for a new line t for a tab to get a double quote to get a single quote to get a backslash Strings We have seen the String type and that re represent String literals by putting characters in double quotes Escape characters can also go inside of normal strings Strings have many methods We can see the basics using tab completion If we put in some extra parentheses Raw Strings There are some situations when using escape characters is a pain For this use triple double quotes to make a raw string Anything you type between the triple double quotes will go into the string They can span multiple lines even Variables It is very common to want to represent values with names A variable is a name that we use to represent a value In Scala we can declare variables using val or var val name Type expression var name Type expression A val can t change it s value a var can The colon and type are generally optional Tuples Another type in Scala is the Tuple type A tuple has comma separated values in parentheses They give us a way to handle a fixed set of associated values Assignment into a tuple does pattern matching Minute Essay What question do you have about the topics we have looked at
View Full Document
Unlocking...