Tokens And Basic Data Types

C++ CHARACTER SET

Character set is a set of valid characters that a language can recognize. A character represents any letter, digit or any other special character. The C++ programming language also has some character set. Now let us learn C++ language character set.

• Letters A–Z, a–z

• Digits 0–9

• Special Characters Space + - * / ^ \ ( ) [ ] { } = ! = < > . ‘ “ $ , ; : % ! & ? _ # <= >=@

• White spaces Horizontal tab (→), Blank space, Carriage return (< ) Newline, form feed

• TOKENS

• 

  A token is a group of characters that logically belong together. The programmer can write a program by using tokens. C++ uses the following types of tokens.

  • Keywords

  • Identifiers

  • Literals

  • Punctuators

  • Operators

    There are some reserved words in C++ which have predefined meaning to complier called keywords. Some commonly used keywords are given
    below:

  • Keywords

Identifiers
Symbolic names can be used in C++ for various data items used by a programmer in his/her program.
A symbolic name is generally known as an identifier. The identifier is a sequence of characters taken from C++ character set. The rules for the formation of an identifier are:
(i) An identifier can consist of alphabets, digits and/or underscores.
(ii) It must not start with a digit.
(iii) C++ is case sensitive, i.e., upper case and lower case letters are considered different from each other. It may be noted that TOTAL and total are two different identifier names.
(iv) It should not be a reserved word (keywords).

• Literals

• Literals (often referred to as constants) are data items that never change their value during the execution of the program. The following types of literals are available in C++.

• integer-constants

• character-constants

• floating-constants

• string-literals
  Integer constants
  Integer constants are whole numbers without any fractional part. It may contain either + or – sign, but decimal point or commas does not appear in any integer constant. C++ allows three types of integer constants.

• decimal (Base 10)

• octal (Base 8)

• hexadecimal (Base 16)
  Decimal integer constants
  It consists of sequence of digits and should not begin with 0 (zero). For example 124, - 179, + 108.
  Octal integer constants
  It consists of sequence of digits starting with 0 (zero). For example, 014, 012.
  Hexadecimal integer constant
  It consists of sequence of digits preceded by ox or OX. For example OXD, OXC. The suffix l or L and u or U attached to any constant forces it to be represented as a long and unsigned respectively.
  Character constants
  A character constant in C++ must contain one or more characters and must be enclosed in single quotation marks. For example ‘A’, ‘9’, etc. C++ allows nongraphic characters which cannot be typed directly from keyboard, e.g., backspace, tab, carriage return etc. These characters can be represented by using an escape sequence. An escape sequence represents a single character. The following table gives a listing of common escape sequences.
  List of escape sequence

• 

  • Punctuators
    The following characters are used as punctuators in C++.

  • Brackets [ ] opening and closing brackets indicate single and multidimensional array subscript.

  • Parentheses ( ) opening and closing brackets indicate functions calls, function parameters for grouping expressions etc.

  • Braces { } opening and closing braces indicate the start and end of a compound statement.

  • Comma , it is used as a separator in a function argument list.

  • Semicolon ; it is used as a statement terminator.

  • Colon : it indicates a labelled statement or conditional operator

  • Asterisk* it is used in pointer declaration or as multiplication operator.

  • Equal sign \= it is used as an assignment operator.

  • Pound sign # it is used as pre-processor directive.

  • Operators

  • Operators are special symbols used for specific purposes. C++ includes many operators.

  • Arithmetical operators

  • Relational operators

  • Logical operators

  • Unary operators

  • Assignment operators

  • Conditional operators
    Floating constants
    Floating constants are also called real constants. These numbers have fractional parts. They may be written in fractional form or exponent form. A real constant in fractional form consists of signed or unsigned digits including a decimal point between digits. For example 3.0, -17.0, -0.627 etc.
    A real constant in exponent form has two parts: a mantissa and an exponent. The mantissa is either an integer or a real constant followed by letter E or e and the exponent which must be an integer. For example 2E03, 1.23E07.
    String Literals
    A sequence of character enclosed within double quotes is called a string literal. String literal is by default (automatically) added with a special character ‘\O’ which denotes the end of the string. Therefore the size of the string is increased by one character. For example “COMPUTER” will be represented as “COMPUTER\O” in the memory and its size is 9 characters.
    Logical operators
    The logical operators are used to combine one or more relational expression.
    List of logical operators
    Operators Meaning
    || OR
    && AND
    ! NOT
    The NOT operator is called the unary operator because it requires only one operand.
    Unary operators
    C++ provides two unary operators for which only one variable is Required.Here plus sign (+) and minus sign (-) are unary because they are not used between two variables.
    Assignment operator
    The assignment operator ‘=’ stores the value of the expression on the right hand side of the equal sign to the operand on the left hand side.
    Conditional operator
    The conditional operator ?: is called ternary operator as it requires three operands. The format of the conditional operator is: Conditional_expression? expression1 : expression2;
    If the value of conditional_expression is true then the expression1 is evaluated, otherwise expression2 is evaluated.

  • The comma operator
    The comma operator gives left to right evaluation of expressions. It enables to put more than one expression separated by comma on a single line

BASIC DATA TYPES

Now you will learn about basic data types used in C++ language. Every program specifies a set of operations to be done on some data in a particular sequence. However, the data can be of many types such as a number, a character, boolean value etc. C++ supports a large number of data types. The built in or basic data types supported by C++ are integer, floating point and character type. A brief discussion on these types is given below:

Data Types with Range

Data Type Range

char –128 to 127

int –32768 to 32767

short int –32768 to 32767

long int –2147483648 to 2147483647

float –3.4 × 10–38 to 3.4 × 10 38

double 1.7 × 10–308 to 1.7 × 10 308

long double 1.7 × 10–4932 to 1.7 × 10+4932

Integer type (int)

An integer is an integral whole number without a decimal point. These numbers are used for counting. For example 26, 373, –1729 are valid integers. Normally an integer can hold numbers from –32768 to 32767. However, if the need be, a long integer (long int) can also be used to hold integers from –2, 147, 483, 648 to 2, 147, 483, 648.

Floating point type (float)

A floating point number has a decimal point. Even if it has an integral value, it must include a decimal point at the end. These numbers are used for measuring quantities. MODULE – 3 249 Introduction to C++ Computer Science Programminig in C++ Notes Examples of valid floating point numbers are: 27.4, -927., 40.03 A float type data can be used to hold numbers from 3.4*10–38 to 3.4*10+38 with six or seven digits of precision. However, for more precision a double precision type (double) can be used to hold numbers from 1.7*10–308 to 1.7*10+308 with about 15 digits of precision.

Character Type (Char)

It is a non numeric data type consisting of single alphanumeric character. Examples of valid character types are : ‘A’, ‘9’, ‘P’, ‘8’, ‘&’. It may be noted here that 9 and ‘9’ are of different data types. The former is of type int and later of type char.