CHAPTER 2: NOTES

Basic Data Types

Introduces a series of data types that includes numbers, characters, user defined ennumerated types and pointers.
Native to most programming languages.
Each basic data type includes data and operations: the components of an abstract data type.
Number, character and pointer types describe simple data because they cannot be divided into simpler parts.
Structures data types have components built from simpler types with rules to define relationships among components. Examples: arrays, strings, ,records, files, lists, stacks, queues, trees, graphs, and tables.
Most programming languages provide library functions to handle arrays, strings, records and files. These are identified as built in structured constructs.

2.1

positive or negative whole numbers that consist of a sign and a sequence of digits.
Referred to as signed numbers.
examples of integer constants:
+35, -278, 19, -28976510.

ADT integer is{ Data Operations.

Assume that u and v are integer expressions, and N is an integer variable.
Compute the quotient using integer division u/v. Input: Two integer values, u and v. Preconditions: Denominator v cannot be 0. Process: Divide v into u using integer division. Output: Value of quotient. Post Conditions: Error conditions exists if v=0. }end ADT

Computer Storage of integers

Stored as binary numbers.
13₁₀= 1(2³)+1(2²)+0(2¹)+1(2⁰)=1102₂
Binary digit is called a bit.
Unsigned numbers represent positive numbers.
8 bits = 1 byte: range 0 to 2⁸-1. (unsigned)
-2⁷ to 2⁷-1. (signed)
2 bytes: 0 to 2¹⁶-1.
(short int) -2¹⁵ to 2¹⁵-1.
4 bytes: 0 to 2³²-1.
(long int) -2³¹ to 2³¹-1.
Int types in C++: Integer, short integer, long integer.

2.2 Character Types.

ADT character is{
  Data
    ASCII character set
  Operations
    Assignment
       A character value can be assigned to a character variable.
  Relational
   The six standard relational operators apply to characters using the ASCII
   dictionary order relation end ADT.
   ASCII: Coding scheme using a 7 bit integer code.
   Table 2.2 Page 44.
   Table 2.3 Page 45.
   Type  char is used to store a character.
	}end ADT

2.3: Real Data Types

ADT: Page 46.
1101.1101₂=1(2³)+0(2²)+1(2¹)+1(2⁰)+1(2^-1)+1(2^-2)+0(2^-3)+1(2^-4)=11.8125₁₀
C++ supports float, double and long double.

2.4 Enumerated Types.

ADT Enumerated is{
  Data
    User defined list of N distinct items.
  Operations
    Assignment
       A variable of enumerated types can be assigned any of the items
       in the list. 
  Relational:
    The six standard relational operators use the order relation
    determined by the way in which items are listed.
       } end ADT.

Example 2.5:

enum Boolean {False, True};
Boolean done=False;
enum Month{Jan=1, Feb, Mar....Dec};
Month Mon=Dec;

2.5 Pointers:

ADT Page 50.
Pointer value is a memory address that uses 16, 32 or more bits depending on machine architecture.
char str[]="ABCDEFG";
char*PC=str; //PC points to string str
short X=33; short*PX=& X; // PX points to short X

The following statements illustrate fundamental pointer operations.
cout <<*PC<<endl;//Print `A'
PC+=4; //Move PC right 4 chars.
cout <<*PC<<endl;//Print `E'
PC--;//Move PC left 1 char
cout <<*PC<<endl;//Print `D'
cout <<*PX+3 <<endl;//Print 36=33+3

				
ADT string is
 Data
         A string is a sequence of characters with an associated length.
         The string structure may have a NULL-terminating character or
	 a separate length parameter.
 Operations

	Length
    Input: None
    Preconditions: None
    Process: For a Null-terminating string, count the
	     characters up to the NULL character;
	     for a length count string, retrieve the length value.
    Post Conditions: None
    Output: Return the string length.

	Copy
    Input: Two strings STR1 and STR2. STR2 is the source and
	    STR1 is the destination.
    Preconditions: None
    Process: Copy the characters from STR2 to STR1.
    Post Conditions: A new string STR1 is created with the
	             length and data obtained from STR2.
    Output: Return access to STR1.

				
	Concatenation
    Input: Two strings STR1 and STR2. Join STR2 onto
			    the tail of STR1.
    Preconditions: None
    Process: Find the end of STR1. Copy characters from
	     STR2 onto the tail of STR1. Update information on the length
             of STR1.
                              
    Post Conditions: STR1 is modified.
    Output: Return access to STR1.


	Compare
    Input: Two strings STR1 and STR2. 
    Preconditions: None
    Process: Apply ASCII order to the strings. 
    Post Conditions: None.
    Output: Return a value as follows.
            STR1 less than STR2: return a negative value.
            STR1 equal to STR2: return a value 0.
            STR1 greater than STR2: return a positive value.


	Index
    Input: A string STR and a single character CH.
    Preconditions: None
    Process: Search STR for the input character CH.
    Post Conditions: None.
    Output: Return the address of the location
            containing the first occurence of CH in
            STR or 0 if the character is not found.


	Right Index
    Input: A string STR and a single character CH.
    Preconditions: None
    Process: Search STR for the last occurence of character CH.
    Post Conditions: None.
    Output: Return the address of the location
            containing the last occurence of CH in
            STR or 0 if the character is not found.

	Read
    Input: The file string from which the characters are read
           and the string STR to hold the characters.
    Preconditions: None
    Process: Read a sequence of characters from the stream
             into the string STR.
    Post Conditions: The string STR is assigned the
                     characters read.
    Output: None.

	Write
    Input: A string that contains characters for output
           and a stream to which characters are written.
    Preconditions: None
    Process: Send the string of characters to the stream.
    Post Conditions: None
    Output: The output stream is modified.
end ADT String

ADT Record is
  Data
    An item containing a set of fields of heterogenous type.
    Each field has a name that allows for direct access to
    data in the field.
  Operations
     Access Operator
    Preconditions: None
    Input: Record name (recname) and field.
    Process: Access data in the field.
    Output: When retrieving data, return the field value
    to the client.
    Post Conditions: When storing data the record is changed.
    end ADT Record

ADT File is Data An identification of the external file and the direction of the data flow. A sequence of characters that are read from or written to the file. Operations Open Input: Name of the file and the direction of flow. Preconditions: For input, the external file must exist. Process: Link a stream with the file. Output: A flag that indicates the operation is successful. Post Conditions: Data may flow between the external file and system memory through the stream. Close Input: None Preconditions: None Process: unlink the stream from the file. Output: None. Post Conditions: Data may no longer flow through the stream between the external file and system memory.

Read Input: An array to hold blocks of data; A count N Preconditions: The stream must be open with read-only or read-write direction. Process: Input N characters from the stream into the array. Stop on end-of-file Output: Return the number of characters that are read. Post Conditions: The file pointer is moved forward N characters.

Write Input: An array; A count N Preconditions: The stream must be open with write-only or read-write direction. Process: Output N characters from the array into the stream. Output: Return the number of characters that are written. Post Conditions: The stream contains the output data and the file pointer is advanced forward N characters.

Seek Input: Parameters to reset the file pointer. Preconditions: None. Process: Reset the file Pointer. Output: Return a flag that indicates whether the seek is successful. Post Conditions: A new file pointer is set. end ADT File