C++ Character Set

             Like the C language, C++ also comprises a character set from which the tokens (basic types of elements essential for programming coding ) are constructed. The character set comprises of “A” .. “Z” , “a” .. “z”, 0 .. 9, +, -, /, *,\, (, ), [, ], {, }, =, !=, <, >, . , ’ “ ; : %, ! , &, ?, _, #, <=, >=, @, white space, horizontal tab, carriage return and other characters.

           A quick recap of the basic types : The basic types are collectively called as TOKENS. A token is the smallest individual unit in a program. Tokens are classified as shown in Figure. 

Classification of Tokens

1. Keywords

Keywords have special meaning to the language compiler. These are reserved words for special purpose. These words cannot be used as normal identifiers. The following Table shows the list of keywords used in C++.

auto break case const class

continue default delete do else

enum for friend goto if

inline new operator private protected

public return signed sizeof static

struct switch this unsigned virtual while

2. Identifiers

Identifiers are also called as variables. Variables are memory boxes that hold values or constants. A variable name must begin with an alphabet or underscore followed by alphabets or numbers. For example _test ; test ; sum12 are some valid identifiers. We shall see more about variables after dealing with data types

3. Constants

Constants are data items whose values cannot be changed. A constant is of numeric or non-numeric type. Numeric constants consist of only numbers, either whole numbers or decimal numbers. Integer, floating-point are numeric constants.

3.1 Integer Constant

·         Integer Constant must have at least one digit and must not contain any fractional part.

·         May be prefixed with a + or – sign

·         A sequence of digits starting with 0 (zero) is treated as Octal constant Ex. 010 = 8 ( [8] 10 = [10] 8 )

·         A sequence of digits starting with 0x is treated as hexadecimal integer. Ex. 0xF = 15 ([15] 10 = [F] 16 )

3.2 Floating Point Constant

Floating Point Constant is a signed real number. It includes an integer portion, a decimal point, a fractional portion and an exponent. While representing a floating point constant the integer portion or the decimal portion can be omitted but never both. For example 58.64 is a valid floating point (Real) constant. It can be represented in exponent form as follows :

·         5.864E1 => 5.864 x 101 => 58.64

·         5864E-2 => 5864 x 10–2 => 58.64

·         0.5864E2 => 0.5864x102 => 58.64

The letter E or e is used to represent the floating-point constant exponent form.

3.3 Character Constant

Character constant is a constant that contains a single character enclosed within single quotes. It can be any character as defined in the character set of C++ language (alphabet, numeral, mathematical, relational or any other special character as part of the ASCII set). Certain special characters like tab, backspace, line feed, null, backslash are called as non-graphic character constants. These characters are represented using escape sequences. Escape sequences are represented using characters prefixed with a backslash. The following Table shows the escape sequences.

3.4 String Literal

String Literal is a sequence of characters surrounded by double quotes. String literals are treated as array of characters. Each string literal is by default added with a special character ‘\0’ which marks the end of a string. For example “testing”

4. Operator

Operator specifies an operation to be performed that yields a value. An operand is an entity on which an operator acts. For example:

RESULT = NUM1 + NUM2

NUM1 and NUM2 are operands. + is the additional operator, that performs the addition of the numbers. The result (value) generated is stored in the variable RESULT by virtue of “=” (Assignment) operator. The following Table shows the operators in C++.

The following operators are specific to C++.

::          .*          ->*

The operators # and ## are used only by the preprocessor.

Operators are classified as

·         Arithmetic

·         Assignment

·         Component Selection

·         Conditional

·         Logical

·         Manipulator

·         Member dereferencing

·         Memory Management

·         Preprocessor

·         Relational

·         Scope Resolution

·         Shift

·         Type Cast

Based on operand requirements, operators are also classified as unary, binary and ternary operators. 

• Unary operators require one operand
• Binary operator requires two operands
• Ternary operator requires three operands 

4.1 Arithmetic Operators

Arithmetic Operators are used to perform mathematical operations. The list of arithmetic operators are:

·         +

·         -

·         * multiplication operator

·         / division operator

·         % modulus operator - gives the remainder of

·          integer divison

·         += , -=, *= , /= , %=

Arithmetic expressions are formed using arithmetic operators, numerical constants/variables, function call connected by arithmetic operators.

Examples :

·         a = -5;

·         a = +b;

·         a /= 5; (a = a/5)

·         a++; (Post increment operator . Equivalent to a = a+1)

·         a— ; (Post decrement operator. Equivalent to a = a-1)

·         ++a; (Pre increment operator. Equivalent to a = a+1)

·         —a ; (Pre decrement operator. Equivalent to a = a – 1)

·         a *= 2 ( a = a * 2)

·         a %= 5 ( a = a/5)

·         a = b + pow(x,y) ( a = b + x y )

Operators are executed in the order of precedence. The operands and the operators are grouped in a specific logical way for evaluation. This logical grouping is called as association. Table indicates the Mathematical Operators, its Type, and Association.

Expression	Operation	Example
a++	Get the value of a, then increment the value of the variable by 1	a =5; c = a++ Execution : c = a; a = a+ 1; Hence the value stored in the variable c is 5.
++a	Increment the value of the variable a by 1, and then get the value	a = 5; c = ++a; Execution: a=a+1 c = a; Hence the value of c will be 6
a--	Get the value of a, then decrement it by 1	a = 5; c = a--; Execution : c = a; a = a –1 What will be the value of c?
--a	Decrement the value of a by 1, then get the value of a	a = 5 c= --a; Execution : a = a – 1 c = a; What will be the value of c?

4.2 Relational Operators

Relational Operators are used to compare values. The list of relational operators are:

·         = = equal to

·         > greater than

·         < lesser than

·         >=, <= greater than or equal to , lesser that or equal to

·         != not equal to

Relational operators are used to compare numeric values. A relational expression is constructed using any two operands connected by a relational operator. For example the relational operators are used to construct conditions such as

·         10 > 20

·         500.45 <= 1005

·         99 != 99.5

·         9 = = 9

The result of a relational operation is returned as true or false. The numeric constant zero (0) represents False value, and any nonzero constant represents true value. The above expressions output will be

·         0 (10 > 20 is false ) ;

·         1 ( 500.45 < 1005 is evaluated to True hence any non zero constant) ;

·         1 (99 != 99.5 will be evaluated to True hence non zero constant)

·         1 ( 9 = = 9 will be evaluated to true, hence the output will be non zero constant)

4.3 Logical Operators (Boolean Operators)

Logical operators combine the results of one or more conditions. The various logical operators are && (AND) , || (OR) , ! (NOT)

Example : c = 5 , d = 6 , choice = ‘y’, term = ‘2’ (Assume True is indicated as 1 and False as 0)

Result_1 = (c = = d) && (choice != term)

Result_2 = ( ‘y’ = = ‘Y’) || (term != ‘0’)

Result_3 = (c = = d) && ‘(y’ = = ‘Y’ )|| choice != term

Result_4 = (c = = d) || (‘y’ = = ‘Y’) && choice ! = term

The values stored in Result_1 is 0 (False), Result_2 is 1 (True), Result_3 is 1 (True) and Result_4 is 0 (False).

4.4 Conditional Operator (?:)

(num1 > num2) ? “true”:”else” - ?: Is a ternary operator – (num1>num2,”true”,”false” are the operands. A ternary operator ( ?:) is also called as conditional operator. The general syntax is E1 ? E2 : E3 where E1,E2,E3 are operands. E1 should essentially be of scalar type, E2 and E3 are values or statements. For example to assign the maximum value of the two values one can express it as:

max = (num1 > num2) ? num1 : num2; The variable max will take the value of num1 if num1 is greater than num2, otherwise max will be assigned with the value of num2.

4.5 Assignment Operators

= is the simple assignment operator. It is used to assign the result of an expression (on the right hand side) to the variable (on the left hand side of the operator). In addition to the simple assignment operator, there are 10 ‘shorthand’ assignment operators. Refer to the following Table for all assignment operators.

Expression	Working	Result
A=5	The value 5 is assigned to the variable A.	The variable takes the value 5.
A += 2	A+= 2 is interpreted as A = A +2	The value stored in A is 7
A - = 2	A = A – 2	The value stored in A is 3
A *= 4	A = A * 4	The value stored in A is 20
A /= 2	A = A / 2	The value stored in A is 2
A %= 2	A = A % 2	The value stored in A is 1

The following Table gives the complete Operator precedence of all operators used in C++.

 

5. Punctuators

Punctuators are characters with a specific function. Refer to the following Table for Punctuators and their Purpose.

Punctuators	Purpose
;	Terminates a C++ statement
//	Treats statements prefixed with this as comments
/* */	Blocks enclosed within these characters are treated as comment
{ }	Used to group a set of C++ statements. Coding for a function is also enclosed within these symbols
[ ]	Index value for an element in an array is indicated within these brackets
‘ ’	Is used to enclose a single cha
“ ”	Is used to enclose a set of characters