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Review

Review. With packagename ; Use packagename ; Procedure procedurename Is declaration of variables & constants Begin statements of program End procedurename ;. Chapter 3. The Basics of Ada. Topics. Standard Types Identifiers Literals Expressions Variables & Constants

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Review

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  1. Review Withpackagename; Usepackagename; ProcedureprocedurenameIs declaration of variables & constants Begin statements of program Endprocedurename;

  2. Chapter 3 The Basics of Ada

  3. Topics • Standard Types • Identifiers • Literals • Expressions • Variables & Constants • Errors in Programs

  4. Data Typescharacterized by… • Values that can be stored as the data type • Operations that can be performed on them • Attributes (properties) associated with each type • ’Last • ’First • ’Digits • ’Pos • ’Val

  5. Types of Data(Incomplete but a beginning)

  6. Numeric Data Integer & Float

  7. Data type: Integer • No fractional part to the number • Usually stored in two bytes (16 bits) • Processed faster than float • Stored as exact value in memory • Limited to –32,768 to +32,767 (if stored as two bytes)

  8. Storing Integer Data Using Binary Number System – 16 bits

  9. Base 2 Uses symbols 0-1 Place value based on powers of 2 Base 10 Uses symbols 0-9 Place value based on powers of 10 Binary Number System vs. Decimal Number System

  10. Decimal Number System(Base 10) Place Value 4 x 103 + 3 x 102+ 0 x 101 + 2 x 100 = 4 x 1000 + 3 x 100 + 0 x 10 + 2 x 1 = 4000 + 300 + 0 + 2 = 4302

  11. Binary Number System(Base 2) Place Value 1 x 23 + 1 x 22+ 0 x 21 + 1 x 20 = 1 x 8 + 1 x 4 + 0 x 2 + 1 x 1 = 8 + 4 + 0 + 1 = 1310

  12. You try one… Change this binary (base 2) integer to a decimal (base 10) number: Sign of number 00000000000100012

  13. Answer: (will be positive) 20 24 100012 = 1 x 24 + 0 x 23 + 0 x 22 + 0 x 21 + 1 x 20 = 1 x 16 + 0 + 0 + 0 + 1 x 1 = 16 + 1 = +17

  14. Package for Integers With ada.integer_text_io; Use ada.integer_text_io; Declaring a variable Count : integer;

  15. Attributes of Integer Data Type • Integer’first – gives smallest possible negative integer • Integer’last – gives largest possible positive integer • Way to find out how your computer stores integers (two bytes, four bytes, etc.) PUT(“the biggest integer is: ”); PUT(integer’last);

  16. Data type: Float • Always stores fractional part to the number • Usually stored in four bytes (32 bits) • Processed slower than integer • Stored as approximate value in memory • Stores the sign (1st bit), exponent(8 bits), and then mantissa (23 bits)…from left to right

  17. Data Type: FloatStoring the number – 32 bits 00000010010100000000000000000000 Sign exponent mantissa 0 00000100 10101000000000000000000 + 4 .10101 = + .10101 x 24 = 1010.1 = 1x23+0x22+1x21+0x20+1x2-1 = 8 + 0 + 1 + 0 + ½ = 9.5

  18. Package for Float With ada.float_text_io; Use ada.float_text_io; Declaring a variable Salary : float;

  19. Attributes of Float Data Type • Float’digits– gives number of significant digits • Float’first – gives smallest possible positive number that can be stored • Float’last – gives largest positive number that can be stored PUT(“the biggest float number is: ”); PUT(float’last);

  20. Text Data Character & String

  21. Data Type: Character • Can store only one letter, digit, special symbol, or non-printable control character • Value of character put in apostrophes – ’d’ Example: to assign the exclamation point to a variable called ch ch := ’!’ • Stored in one byte 01000010 (this is a ‘B’) • Set of characters has order (enumerated) – see appendix F • Can compare one character to another (<, >, =)

  22. Package for Character With text_io; Use text_io; Declaring a variable Ch : character;

  23. Attributes of Character Data Type • ’Pos – gives the ASCII code (position) of the character in the set • Example: ’A’ has position 65 • ’Val – gives the character that goes with a particular code • Example: Put(Character’val(65)); would display the ‘A’

  24. Data Type: String • Used to store more than one character (a string of characters) • Must declare how many characters are possible for the variable

  25. Package for String same as character With text_io; Use text_io; Declaring a variable Name : string(1..8);

  26. Indexing a String(only using part of it) Name(1..2) would only access the first two characters in the string variable Name

  27. Reading text of varying length • Make sure declaration of variable allows for as large a string as needed (Name : String(1..100) • Declare an integer variable to hold the number of characters read in (N) • Use the GET_LINE(Name,N) • Then use indexing to get correct string you want PUT(“the name is ”); PUT(Name(1..N));

  28. Logical Data Boolean (True or False)

  29. Data Type: Boolean • Can be a statement which can be shown true or false • Example: num_of_people > 10 • Can be a variable that is of type boolean • Example: If Found then PUT(“I found it!”); End if;

  30. Identifiers • Way of naming things in the program • Name of procedure • Name of variable • Reserved words (Begin, If, For…etc.) • Must begin with letter of alphabet • Remaining part of identifier must be letters, digits (0 – 9), or underline symbol • Examples: num_of_2nd_place_winners • Case does not matter

  31. Valid or Invalid Identifiers ?? • 7_up • Number1 • Number_1 • My Name • First-Name • _MyName

  32. Literalsactual (constant)values used in a program…must match variable type • 25 integer literal • 3E4 integer literal (same as 30000) • 23.0 float literal • 4.1E-3 float literal (same as 0.0041) • ’R’ character literal • ”Joshua” string literal • false boolean literal

  33. Expressions…Examples • Gross_pay – 0.125 * Gross_Pay • -k • 13 mod 5 • 13 rem 5 • abs k • float(num_of_people) • K>5 (boolean expression)

  34. Expressions Precedence (order) of operators ** abs not * / mod rem + - (unary – sign of number) & + - (ordinary adding and subtraction) = /= < <= > >= in not in And or xor and then or else -5+4*6/2**3

  35. Declaring Variables • Num_of_items : integer; • Address : string(1..30); • Symbol : character; • Temp, max_temp, min_temp : float; • Found : boolean

  36. Initializing variables • Found : boolean := false; • School : string(1..3) := “MSU”; • Rate : float := 0.05; • I_rate : float := Rate * 2

  37. Declaring Constantscannot be changed in program • Max_num : constant Integer := 100; • Max_num : constant := 100; • Int_rate : constant := 0.065; • Title : constant string := “Welcome to Murray!”

  38. Kinds of Errors • Compile-time error –broke the rules of syntax (grammar) – detected during compilation • Run-time error – illegal values occurred – detected during execution • Logic-error – may have mixed up the sequence of statements – a true “bug”

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