Syntax, Data Types, and Declarations

• Syntax: the formal rules governing how valid instructions are written in a programming language.
• Semantics: The set of rules that determines the meaning of instructions written in a programming language.
• Identifier: A name associated with a function or data object used to refer to that function or data object.
  • main
  • variable names.
  • constant names.
• Reserved words:
  • Words that have special meaning in c++.
  • here is a list
    • Note c++ is a living/growing language.
    • Different versions are know as c++xx
    • C++98 was really the first.
    • C++03 was a minor change.
    • C++11 was a major change.
    • C++14, C++17 and C++20 are others
• Syntax rules for identifiers
  • Must start with letter or _
    • But don't use _, that is reserved for compiler things.
  • Can only contain letters, numbers and _
  • Can not be a reserved word.
  • Give some examples of valid and invalid identifiers.
• Conventions for identifiers
  • Should have a meaning.
  • Variables:
    • start with lower case.
    • Each new word starts with upper case.
  • Functions:
    • Start with upper case
    • Each new word starts with upper case.
  • Constants
    • All upper case
    • Words have a _ between them.
  • Give good and bad examples of each.
• Data types
  • We need to tell the compiler what type of data we will be storing.
  • a reference but perhaps not.
  • Basic:
    • int
      • Integer: a whole number.
      • -2, 0, 130
    • float
      • A number in scientific notation.
      • 0.34
      • 3.4x10²²
    • char
      • A character.
      • inside ''
      • 'a', '6', '.'
      • We will discuss these further in a bit.
    • string
      • Not a built in type.
      • Should use #include <string>
      • A collection of 0 or more characters.
      • "hello", "", "007"
• Declaring items
  • A declaration is a statement that associates an identifier with a data object, function or data type so that the programmer can refer to that item by name.
  • EVERYTHING must be declared before it can be used.
• A variable is a quantity that can change during the execution of a program.
• Syntax for declaring a variable
  • datatype identifier;
  • datatype identifier = value;
  • datatype identifier, identifier, ... , identifier;
  • datatype identifier = value, identifier = value, ... , identifier = value;
  • datatype identifier{value};
  • Or any combination.
  • The last is the current preferred method.
• In general, it is best to initialize everything when it is declared.
• Declaring a constant
  • const datatype identifier = value;
  • const datatype identifier {value};
  • const datatype identifier = value, identifier = value, ...;
  • const datatype identifier {value}, identifier {value} , ...;
• Declare the following variables
  • An integer to hold the player's age.
  • A string to hold the player's name.
  • A float to hold the the current interest rate.
  • A character to hold the player's middle initial.
• Constants are used in a program when there is a value that will only change when the program is recompiled.
• Constants should be used anytime a value has a name.
  • const int MAX_PEOPLE = 5;
• Silly constants should not be declared however
  • const int FIVE = 5;
  • const FIRST_CONSTANT = 42;
• Declare a constant to
  • Hold the legal age to drive a car, an integer 16 in pa.
  • Hold the current interest rate, 3.45%, a floating point number.
  • Hold the word "yes".
  • Hold the number 7.