Tokens

Identifiers are tokens that represent names. These names can be assigned to variables, methods, and classes to uniquely identify them.

• Variables - are names that represent memory locations in a computer. For example I could create a variable called "Celsius Temp" to hold data about the current temperature in Celsius or "FarenTemp" to hold data on the current temperature in Fahrenheit. When a programmer  wishes to perform some operation using a variable, he or she is actually performing an operation on data that exists at that memory location. For example, these lines could be inserted into a typical program to convert  a Fahrenheit temperature of 21 degrees to Celsius.
   
  • Celsius Temp = 21;
    FarenTemp = (9/5 * Celsius Temp) + 32;

• In the first statement, the number value of 21 is stored in the memory location Celsius Temp.
• In the second statement the data in the Celsius Temp location is multiplied by 9/5 and then 32 is added. This total is then stored in the memory location called FarenTemp.

• Functions - are tasks within a program. A function also must have a name. You could for example create a method called "ConvertToFarenheit". This name would be assigned to the task responsible for converting Celsius temperatures to Fahrenheit.
• Classes - are a grouping of related data structures or methods. For example you could create a class called "Temperature". Within this class would be methods that are used to do temperature related operations such as "ConvertToFarenheit" or "GetCurrentTemperature".

Different programming languages have different rules about the use of Identifiers. In C/C++, all identifiers are case sensitive (i.e.. temp and Temp are not the same). Identifiers must begin with a letter. You can include numbers in an identifier but not as the first character. In addition, identifiers cannot have any spaces in them (i.e.. Celsius Temp is invalid).

Keywords are predefined identifiers reserved by languages for a specific purpose and are used only in a limited, specified manner. You cannot use keywords for any other purpose. Listed below are Keywords reserved by the C++ language.
 

Literals are character constants that have a special meaning in a language. Listed below are several literals used in C++.

• \n   newline
  \b   backspace
  \f    formfeed
  \0   null
  \r   carriage return
  \t   horizontal tab

Operators specify an evaluation or computation to be performed on data. Indicated below are several operators and their meaning as used in C++.

• -     Subtraction
  +     Addition
  *     Multiplication
  /      division
  %    Modulus
  --     Decrement
  ++   Increment
  >     Greater Than
  <     Less Than
  >=   Greater Than or Equal To
  <=   Less Than or Equal To
  ==   Equal To
  !=    Not Equal To
  && And
  ||     Or
  !     Not

Separators are used to inform the compiler of how things are grouped in the code. Listed below are examples of  separators supported by C++.

All comments written within the source code of a program are ignored. To notify the compiler that the text is in fact a comment, several symbols are used. These symbols are indicated below.

•  /* comment */ All characters between /* and */ are ignored.
  // comment  All characters after the // up to the end of the line are ignored.