Decoding the Structure of C++ Program: A Comprehensive Guide in 2023

The Structure of C++ Program

The structure of C++ program contains:

• Include files.
• Class declarations
• Member function definitions
• Main Function

#include<iostream>
#include<string>
using namespace std;
class<class-name>
{
      [private:]
      member declaration;
      [protected:]
      member declaration;
      [public:]
      member declaration;
};
[class member function declarations]
---
---
int main()
{
    statements;
    ---
}
[other user defined functions]
---
---

Tokens in C++

Tokens are smallest individual units in a program.

• Tokens in C++ are
  1) Keywords
  2) Identifiers (Variables)
  3) Literals (Constants)
  4) Strings
  5) Operators
  6) Punctuators & Special Symbols
• C++ program consists of tokens, white spaces and syntax of the language.

Keywords in C++

• Many of the keywords in C and C++ are common.
• Keyword implements the language features.
• Keywords are the identifiers reserved by language.
• Keywords have predefined meaning to compiler. They cannot be used as variable names or other user defined program elements.
• Following is the list of C++ keywords:

asm        auto       break      case
catch      char       class      const
continue   default    delete     do
double     else       enum       extern
float      for        friend     goto
if         inline      int        long
new        operator   private    protected
public     register   return     shot
signed     sizeof     static     struct
switch     template   this       throw
try        typedef    union      unsigned
virtual    void       volatile   while  

• ANSI C++ added keywords are:

bool           const_cast   dynamic_cast
explicit       export       falsemutable
namespace      true         typename
static_cast    typeid       wchar_t
reinterpret_   cast

Identifiers in C++

• Identifier is a common term that represents name of variable, name of function, name of array, name of classes or in general any user defined element.
• Identifier is a fundamental requirement of programming language.
• An identifier can consists of alphabets,digits and underscores.

Variable in C++

• Variable is the name given to the memory location that stores data.
• Variable is a data item whose value varies during the program. Each variable used in program must be declared at the beginning of the function.
• All the variables must be declared before their use.
• The declaration syntax for variable is
  data_type<variable_name>;
  where data_type is any valid C++ datatype.
• Variable declaration does two things.
  a) It tells the compiler what the variable name is, and
  b) It specify what type of data the variable will hold.
• An integer variable holds integer constant, floating point variable hold float(real) value etc.
• A variable may be local or global.
• According to storage type, variable may be auto, external, static or register.
• Variable definition ends with semicolon.
• The value of variable can be changed in a program.
• Example.
  Int a, b, c=45;
  float p,q,r=2.5;
  char z=’#’;

Literals in C++

• As per google character literals is a type of literal in programming for the representation of single characters value within source code of a computer program.
• Literals are the data items whose value remains unchanged throughout the program execution.
• They refer to fixed values.
• C++ supports several type of literal;
  1. Integer constant
  2. Character constant
  3. Floating point constant
  4. String constant.
• Example:
  1234 Decimal integer constant
  123.456 Floating pint integer constant
  O52 Octal integer constant
  OX25 Hexadecimal integer constant
  “Bangalore” String Constant
  ‘H’ Character constant

Symbolic Name in C++

• Symbolic name is the name declared at the beginning of the program and assigned a constant value.
• It is defined using preprocessor directive as below:
  #define symbolic_name value
• Generally symbolic name are written in uppercase to visually distinguish them from other variables.
• Its definition does not end with semicolon.
• These are not declared for any data type.
• In the program we can not change the value of symbolic constant.
• Example:
  #define MAX 100
  #define PI 3.1415
  #define TOTAL_MARKS 50

Punctuators and Special Symbols

• [ ] Square bracket – These are used to indicate single and multidimensional array subscript.
• ( ) Round bracket or Parentheses – These are used to indicate function calls.
• { } Curly bracket or braces – These are used to indicate the start and end of a block or a compound statement.
• ,Comma – This is used to separate arguments in a list.
• * Asterisk – This is used to indicate pointer declaration.
• = equals to – This sign is used as an assignment operator.
• # Pound – This is used as pre-processor directive.

Rules for Constructing Variable Name

• Variable name may be a combination of alphabets (a—z, A…Z), digits (0…9) or underscores ( _ ).
• Sometimes, compiler in which case its length should not exceed 8 characters impose an additional constraint on the number of characters in the name.
• First character must be alphabet or an underscore.
• No comma or blank space is allowed.
• Among the special symbols, only underscore can be used in variable name.
• No word, having a reserved meaning in C++can be used for variable name.
• C++ distinguish between uppercase and lowercase characters.
• Variable name cannot start with a digit.
• In ANSI C++, there is no limit on the length of the variable name.
• Example:
  roll_Number
  name
  city
  mark1
  mark2
  address
  employee_name