1. Data Types Copyright © 2006 Patrick McDermott College of Alameda pmcdermott@peralta.edu

2. Fact  CRC Cards : (Attribute)  ERD : Attribute  Relational : Attribute  Database : Column  Programmer : Variable  UML : Property  Etc., etc., etc. …: Field, Item, Element

3. The Rules C++ Allowed/Forbidden characters –Letters, Numerals, _ –NO Spaces Break_character: Underscore _ –No initial numeral Length, Very Long Case SeNsItiVe Cannot be a Keyword (Keywords are Reserved Words)  Nouns for Variables/Classes  Verbs for Functions/Methods

4. The Rules Java Allowed/Forbidden characters –Letters, Numerals, $, _ –NO Spaces Break_character: Underscore _ –No initial numeral Length, Very Long Case SeNsItiVe Cannot be a Keyword (Keywords are Reserved Words)  Nouns for Variables/Classes  Verbs for Functions/Methods

5. Numbers, Text & Truth Numbers –int or double Text –char or string –C#: char is 2 bytes in C++ wchar_t Booleans –Logical: true or false. We might not have beauty, but it does have truth. Decimal (.NET) –± $792,281,625,142,643,375,935,439,503.35m –± 79,228,162,514,264,337,593,543,950,335M

6. 2 Kinds of Numbers Integers int A counting number A whole number Discrete No fraction No decimal 2 3 9 Floating Point float, but use double A measuring number A fractional number Continuous Fraction Decimal 2½, 3.14159, 99.99 3.0 too!

7. Numbers Integers: int @ 4 billion –2,147,483,648 to +2,147,483,647 0-4.3 billion if unsigned Not enough bils for Bill’s fortune Double-Precision Floating-Point: double –Range: Big enough You can enumerate all the atoms in the Universe. –Precision: at least 15 decimal digits Just enough for $Trillion to the cent. $1,234,567,890,123.45 Not quite enough for a credit card number

8. I Declare! String s; String s = "Hi"; int x = 0; double x, y; int x = 0, y = 1; final int MYNUMBER = 0; The Unchanging const ant ALLUPPERCASE or ALL_UPPER_CASE

9. I Declare! string s; string s = "Hi"; int x = 0; double x, y; int x = 0, y = 1; const int MYNUMBER = 0; The Unchanging const ant ALLUPPERCASE or ALL_UPPER_CASE extern int SOMEWHERE_NOT_HERE; In compliment extern, ’tis not long after But I will wear my heart upon my sleeve—Iago, Otello I.1.

10. Number versus Character Sort As numbers, one & two & three are binary 1 and 10 and 11. As text, 1 & 2 & 3 are ASCII characters 49 & 50 & 51. Numbers sort by value. Text sorts character by character. You can be richer than Bill Gates! As text, $9 is greater than $80,000,000,000! So, just keep $9, and sort net worth as text!

11. Precision Values of type float have seven digits of precision. Values of type double have 15-16 digits of precision. Values of type decimal are represented as integer values that are scaled by a power of 10. Values between -1.0 and 1.0 are represented exactly to 28 digits.

12. Size not Standard Each computer system is different. Types are based on the system Word. We are on a 32-bit (4-byte) system, So int is a word (4 bytes), double is 2 words (8 bytes)… TypeSize char, unsigned char, signed char 1 byte short, unsigned short 2 bytes int, unsigned int 4 bytes long, unsigned long 4 bytes float 4 bytes double 8 bytes long double 8 bytes

13. The incredible Growing int Windows 3.11 (and earlier) The 16-bit Windows A 2-byte system word Windows 95 (and later) The 32-bit Windows A 4-byte system DWord C Standard for int : The short must not be longer than the int The long must not be shorter than the int short int long short int long Windows 7 & Java (and later) The 64-bit Windows A 8-byte system QWord short int long

14. Alphanumeric Text String s Single character or a string of characters? 'a' is the single character known as a "a" is a character string consisting of the letter a A C string is actually a null-terminated array It needs a space for the null (binary zeroes) "a" is 2 characters long: a + null lpsz “long pointer to a null-terminated string” [yuck!] String Theory Strings have been a sore point, with me & others Unnecessarily overcomplicated What were they thinking???