CIS-60 Home http://www.c-jump.com/CIS60/CIS60syllabus.htm

C++ Fundamental Types and Declarations

1. "Something in memory"
2. Introduction
3. Introduction, declared variables
4. Every name has a type
5. Type determines operations
6. C++ Fundamental Types
7. Boolean Type
8. Boolean to integer conversion
9. Character Data Type
10. Character Set
11. Character Literals
12. Character Type Example
13. Integer Types
14. Integer Literals
15. Floating-Point Numbers
16. sizeof operator
17. C++ variables
18. Declaration Initializers
19. Variable Names
20. Variable Name Examples
21. Scope of Variables
22. Declaration Is a Statement

1. "Something in memory"

• objects: regions of memory

• variables: access to objects

• C++ types: size + behavior

• declarations: type + name

2. Introduction

• Consider

  
      x = y + 2;
  
  

   

3. Introduction, declared variables

• x and y declared:

  
      double x; 
      int y = 7; 
      x = y + 2;
  
  

   

4. Every name has a type

• Type determines operations

  
      double x;  // declaration of x
      int y = 7; // initialization of y
      x = y + 2; // addition and assignment
  
  

   

5. Type determines operations

• 
  // Example:
  void main()
  {
      double x;  // declaration of x
      int y = 7; // initialization of y
      x = y + 2; // addition and assignment
  }
  
  

6. C++ Fundamental Types

• bool: true or false

• char: characters

• int: integer numbers

• double: floating-point (real) numbers

7. Boolean Type

• Logical operations:

  
      int a = 2; 
      int b = 2; 
      bool is_equal = ( a == b ); 
  
  

• Here, double equal sign operator ( a == b ) is making a decision:

  
      ( a == b ) // Is a equal to b?
  
  

• The result (true in our case) is stored in boolean variable named is_equal.

   

8. Boolean to integer conversion

• Boolean types can be converted to plain integer numbers and back:

  
  void main() 
  {
      int i = -1; 
      bool b = i; // b will be true
      int x = b;  // x will be set to 1
      x = 0;
      b = x;      // b will be set to false
  } 
  
  

• Note: no assumptions should be made regarding the size of bool type. On many systems it takes 8 bits to store a boolean variable.

   

9. Character Data Type

• C++ character is a single character of a character set:

  
      char ch = 'a';
  
  

   

10. Character Set

• Typical character set:

  • 8 bits in size

  • max 256 values

  • Uses ASCII character encoding.

   

11. Character Literals

• Typical character set includes:

  • ' \' ' single quotes

  • '0', '1', '2', ... '9' digits

  • 'A' to 'Z', 'a' to 'z' alphabetic

  • punctuation

  • control characters

  • '\n' newline

  • '\t' horizontal tab

   

12. Character Type Example

• 
  #include <iostream> 
  void main() 
  { 
      char c;                 // Instantiate character variable
      std::cin >> c;          // Input character from the user
      std::cout << c;         // Echo character back to the user
      std::cout << '=';       // Display equal sign
      std::cout << int( c );  // Display character code
      std::cout << '\n';      // Display new line
  } 
  
  

   

13. Integer Types

• 3 forms of integer numbers exist:

  • "plain" int

  • signed int

  • unsigned int

• Integer numbers can have 3 sizes:

  • short int 16 bit

  • "plain" int 32 bit

  • long int 64 bit

   

14. Integer Literals

15. Floating-Point Numbers

• Notations

  • decimal point:

    • 7.33

    • 0.0975

  • float type declares single-precision number

  • double type declares double-precision number

• Example:

  
      double pi = 3.14;
  
  

• More info: floating-point precision

   

16. sizeof operator

• C++ sizes are multiples of char:

  • size of char is 1

  • sizeof ( bool )

  • sizeof ( int )

  • sizeof ( double )

   

17. C++ variables

• All variables must be declared before they can be used in a program:

  
      int counter; 
      int month; 
      int day; 
      int year;
  
  

• Note: C++ declarations end with a semicolon (;)

   

18. Declaration Initializers

• Declaration initializer is an optional part of the variable declaration.

• Initializer provides initial value to our variables:

  
      int counter = 1000; 
      const double pi = 3.14; 
  
  

• Note: const transforms a variable into a constant value...

  • ...once initialized, const variable can never change again.

• Declaration initializer is the only way to set value of a const variable.

19. Variable Names

• Name (identifier) consists of

  • letters ABC... abc...

  • digits 123...

  • underscores _

  • first character must be letter or underscore

  • distinct UPPERCASE and lowercase letters

  • no keywords: const, void, double, int, etc.

   

20. Variable Name Examples

• 
  void main() 
  { 
      const char LF = '\n';
      bool   FLAG_BUSY;
      int    social_security_number;
      double form1040a_field_33;
      bool   FLAG_BUSY = false;  // Error: variable already declared
      bool   flag_busy = false;  // OK, but extremely bad style
      double 1040a_total;        // Syntax error: first character must
                                 // be a letter or underscore 
  }
  
  

21. Scope of Variables

• Declaration placement determines the scope

• Scope establishes visibility of the variable

• Scope limits the lifetime of the variable

22. Declaration Is a Statement