Review of C++

Chapter1: Review of  C++

Program is a sequence of instructions given to a computer to be executed to perform a desired task. Every program is written in some programming language and C++ is such a language developed at AT & T Bell Laboratories by Bjarne Strostrup in the 1980s.

Tokens

They are smallest individual units of a programming language. It is same as words in English and other languages. They are,

·        Key words

·        Identifiers

·        Literals

·        Punctuators

·        Operators

Keywords

They are reserved words for C++ language, which are used for special purposes. There are 48 keywords.

Identifiers

It includes letters and digits used to identify memory locations (variables), or naming a function, labels etc.

Literals

They are represents data items that never change their values during a program run. They are also called constants. They may be numeric literals, character literals, string literal and escape sequence.

Punctuators

They are symbols used as punctuation marks in the syntax of various codes and as separators to enhance program readability. They are, parentheses ( ), brackets [ ], braces { } , ; : * = # (Preprocessor directive).

Operators

They are symbols that are used in operations such as input, output, computation, assignment etc. + - * / % << >> ++ etc are some examples.

Basic Data types and Operators

Data Types

          Data types are the means to identify the type of data and associated operations of handling it. C++ data types are of two types: Fundamental data type and Derived data type.

Fundamental Data Types

          Fundamental data types are those, which represent atomic data items, i.e; the data items that cannot be decomposed of. There are five such data types: ‘int’ for integers, ‘char’ for characters, ‘float’ for real numbers, ‘double’ for real numbers with higher precision and ‘void’ for null set of data.

Derived Data Types

          These data types represent the data items that are composed of the fundamental data types. derived data types in c++ are  structure, arrays and enumeration

1. Arrays: They refer to a named set of finite number of same type of data, each of which can be referenced by mentioning its position (called subscript) in the list. There are one-dimensional and multi-dimensional arrays.

2. Structure: A structure is a group of related data types referenced by a single name. The keyword used is struct.

3. Enumeration: A user can define a set of integer type identifiers in the form of new data types called enumerated data types. The key word used is enum.

Operators

          The tokens that trigger some kind of operations are called operators. An operation requires operator and operands (s). Operands are the data on which the specified task is carried out.

1.   I/O Operators

          The operators for input (cin) and output (cout) operations are >> (called extraction or get from operator) and << (called insertion or put to operator) respectively.

2. Arithmetic Operators

The symbols (or tokens) that trigger computations in the program are called arithmetic operators. They are

Operator	Example a=5, b=2
+ Addition	5+2=7
- Subtraction	5-2=3
* Multiplication	5*2=10
/ Division	5/2=2.5
% Remainder of the division	5%2=1

3. Increment / Decrement Operators

           The Increment operator (++) adds 1 to its operand and Decrement operator (--) subtracts 1 from its operand.

4. Relational Operators

          These operators compare two quantities, that is, they determine the relation between two data. The result of the operation will be either TRUE (1) or FALSE (0). There are six such operators and all of them are binary operators. They are: < (less than), <= (less than or equal to), > (greater than), >= (greater than or equal to), = = (equal to) and ! = (not equal to).

5. Logical Operators

          Logical operators are used to combine relational expressions. The operands as well as the result of these operators are Boolean values (TRUE and / or FALSE). The logical AND (&&), Logical OR (||) and logical NOT (!) are the operators. Consider two relational operations with following output then,

6. Conditional Operator (?:)

          This operator returns a value depending on a condition. It is a ternary operator, which requires three operands to operate upon. The syntax is:

Expression l ? Expression 2 : Expression 3

7. Sizeof() Operator

It is a unary operator that returns the number of bytes occupied by the variable or data type specified within parentheses. For example sizeof (float) returns 4.

8. Comma Operator

It is used to string together several expressions. The group of expressions separated by commas will be evaluated from left to right in sequence and the result of the right most expression will be value of the total comma separated expression.

Expressions

          Operators and operands are combined to form expressions. An expression represents and operation and normally returns a value as the result of the operation. It may be integer expression or real expression or logical expression.

Eg. c=a+b;

Type Conversion

1.   Implicit type conversion (type promotion):

Here the conversion is done by the complier without programmer’s intervention. In this case the complier converts all operands up to the type of the largest operand.

2.   Explicit type conversion (type casting):

Here the user is responsible for the conversion to a specific type.

Control Statements

1.   Selection Statements

          The statements, which alter the normal flow of control based on a condition, are called selection statements. They are also known as conditional statements or decision statements. There are two such statements in C++: if statements and switch statement.

The if Statement

          The ‘if’ statement has three forms: Simple if, if...else, if...else…if ladder.

The syntax of simple if

if (Expression)

{

          Statements;

          }

If the Expression (relational or logical) evaluates to True, the Statement will be executed; otherwise it will be skipped.

The switch statement

          When a number of actions are to be taken based on a number of different conditions, switch statement is the better selection statement.

The syntax is:

Switch (Expression)

          {

          case Constant 1 : Statement Sequence 1;

break;

          case Constant 2 : Statement Sequence 2;

          break;

           _________________

          case ConstantN-1 : Statement SequenceN-1;

          break;

          deafault   :  StatementSequenceN;

          }

2.   Iteration Statements

          Iteration statements allow a set of instructions to be executed repeatedly based on some condition. These statements are also known as looping statements. It has Loop control variable, Initialization expression, test expression, update expression and loop body.

The for loop

The syntax is:

for (Initialization Expression; Test Expression; Update Expression)

{

          body-of the-loop;

}

The while loop

          It is also an entry-controlled loop.

The syntax is:

Initialization expression

while (Test Expression)

{

          loop-body ;

          Updation expression;

          }

The do-while loop

          It is an exit-controlled loop.

The syntax is:

Initialization expression

do

{

          loop-body;

          Updation expression;

          }while (Test Expression) ;

Arrays

It refers to a named list of a finite number of similar data elements. I.e. An array is a collection of same type of data referenced by a common name. It is a collection of continuous memory locations referenced by a common name. Each of the data elements can be referred by set of consecutive numbers, usually 0, 1, 2, 3, 4, ……….., n.

One Dimensional Array

It is the simplest form of an array that can store a linear set of values with one subscript or one index.

Declaration Syntax:

Datatype arrayname[size];

Eg:

Int mark[100];

Multidimensional Array

Eg: Two Dimensional Arrays

                   A 2D array is having rectangular format with rows and columns. It is also known as table. A 2D array a[m][n] is a table with m rows and n columns. It contains m x n elements. Row index starts from 0 to m-1and column size starts from 0 to n-1. Each element has to subscripts. Ie a[0][0], a[0][1],……

Declaration Syntax of 2D arrays

Datatype arrayname [rowsize][columnsize];

Eg:

Int a[10][10];

String as an array

          Strings are group of characters for representing name, house name, city etc. They are represented in double quotes. Eg: “Geetha”, “Dubai” etc. Here a null character terminating character \0 is used to represent the end of the array.

Declaration syntax:

Char name[20];

Functions

To make large programs in to manageable programs, breakdown them in to smaller sub programs is called modularization and the sub programs are called functions.

Functions are classified in to two standard library functions and user defined functions.

User defined functions

A programmer can define their own functions in a program is called user defined functions.

It includes three components, Declaration, definition and Invoking / Calling a function.

Scope rules of functions and variables

Scope of function and variables means the ability to access them in a program. It is classified in to two, Local and Global.

Local variable

The variables declared within a function is said to have local scope. They cannot access these to outside functions.

Global Variables

Variables declared outside the body of function will have global scope. They can access any function in the program.

Types of parameters

The parameters appeared in function call statements is called actual parameters and the parameters appeared in function definition statements is called formal parameters.

These parameters are passed from calling function to function definition in two ways, Call by value and call by reference.

Call by value

In call by value method, copies the value of actual parameters in to the formal parameters are passed. There for any changes made in the formal parameters does not reflect back to the actual parameters.

Call by reference

In call by reference method, address of memory location of actual parameters in to the formal parameters is passed. There for any changes made in the formal parameters will reflect back to the actual parameters.