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 Errors in Programs

Data Types characterized 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

Types of Data (Incomplete but a beginning)

Numeric Data Integer & Float

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)

Storing Integer Data Using Binary Number System – 16 bits

Binary Number System vs. Decimal Number System 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

Decimal Number System (Base 10) x x x x 10 0 = 4 x x x x 1 = = 4302 Place Value

Binary Number System (Base 2) x x x x 2 0 = 1 x x x x 1 = = Place Value

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

Answer: (will be positive) = 1 x x x x x 2 0 = 1 x x 1 = =

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

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);

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 (1 st bit), exponent(8 bits), and then mantissa (23 bits)…from left to right

Data Type: Float Storing the number – 32 bits Signexponentmantissa = x 2 4 = = 1x2 3 +0x2 2 +1x2 1 +0x2 0 +1x2 -1 = ½ = 9.5

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

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);

Text Data Character & String

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 (this is a ‘B’) Set of characters has order (enumerated) – see appendix F Can compare one character to another (, =)

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

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’

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

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

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

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));

Logical Data Boolean (True or False)

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;

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

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

Literals actual (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 ) ’R’ character literal ”Joshua” string literal false boolean literal

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

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

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

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

Declaring Constants cannot be changed in program Max_num : constant Integer := 100; Max_num : constant := 100; Int_rate : constant := 0.065; Title : constant string := “Welcome to Murray!”

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”