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Tokens

As we know,the smallest individual units in a program are known as tokens.Tokens is smallest unit which is easily identifies by C++ compiler.C++ has the following tokens:Keywords
  • Identifiers
  • Constants
  • Strings
  • Operators

 Keywords

Keyword is reserve word that have predefine meaning.Keyword is a word whose meaning is already define to C++ compiler.Keywords can be written is lower case.
Ex:- int,float,double etc.
All C keywords are valid in C++ Keywords.But C++ also contain extra keywords.Ex:- Public,Private,True,False etc.

Identifiers

Identifiers refer to the names of variables,Functions,arrays,classes etc.,created by the programer.They are the fundamental requirement of any language.Each language has its own rules for naming these identifiers.
Rules
  1. Identifiers name also start from alphabet.
  2. No blank space allow between two words.
  3. No special character is allow.
  4. Two words are join with the help of underscore.
EX:- Valid  sum and invalid 4sum.

Variables

Variables is a name that is used to by computer memory to store a value used in a program.
Ex:- a,name, sum etc.

Constants

Contants refer to fixed value that do not change during the execution of a program.
Like C,C++ supports several Kinds of literal constants,They include integers,characters,floating
point number and strings.
Integer constants :- An integer is a whole number without decimal point.It consists of sequence of digits.An integer constants must lie within the range of integer.They can be written in three different number systems:Decimal(base 10),Octal(base 8),Hexadecimal(base 19).
Ex- Valid 23 and Invalid 2,3 .
Floating point constants :- Floating point constants are used to represent real number.It contain decimal point or an exponent sign.
Ex:- 23.35 ,50.78
Character constants :- Character constants is always enclosed in a single (' ').It may be any alphabet,special character ,Digit.Do not be blank space.
Ex:- 'S','1'
String constants :- String constants is always enclosed in a double cotes (" ").It may be any alphabet,special character,digits.
Ex:- "Hello","12345"
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