syntax  :

          datatype variable_name;

 example :

#include <iostream.h>
int main(int argc, char* argv[])
{
    char cLetter='P';
    int iCount=10;
    float fTotal;
    fTotal=100.15;
    cout<<"cLetter = "<<cLetter<<endl;
    cout<<"iCount = "<<iCount<<endl;
    cout<<"fTotal = "<<fTotal<<endl;
    return 0;
}

User defined data types

Class

        A class type is a user-defined composite type. It is composed of "fields" or "members" that can have different types. In a class all members are private by default.

 syntax  :

          class [tag [: base-list ]]
          {
              member-list
           } [declarators];

          [ class ] tag declarators;

  example : 

          class CPerson

          {

              int iAge;

              char cName[15];

              public:

              void getDetails();

          };

Structure : 

        A structure type is a user-defined composite type. It is composed of "fields" or "members" that can have    different types. In C++, a structure is the same as a class except that its members are public by default.

 syntax  :

          struct [tag] { member-list } [declarators];

          [struct] tag declarators;

  example : 

     struct PERSON              

     {   

          int   iAge;              

       float fWeight;

        char  cName[25]; 

     } family_member; 

Union : 

        Unions are class types that can contain only one data element at a time.

syntax  :

        union [tag] { member-list } [declarators];

        [union] tag declarators;

example : 

        union NumericType       

        {   

            int         iValue; 

            long      lValue; 

           double  dValue; 

        };

Usage

#include <iostream.h>
#include <string.h>
class CPerson
{
    int iAge;
    char cName[15];
public:
    void getDetails();
    void showDetails();
};
void CPerson::getDetails()
{
    iAge=27;
    strcpy(cName,"David Beckam");
}

void CPerson::showDetails()
{
    cout<<"Age : "<<iAge<<endl;
    cout<<"Name : "<<cName<<endl;
}

int main()
{
    CPerson Person;  //declaring a variable (object) of user defined type CPerson
    Person.getDetails();
    Person.showDetails();
    return 0;
}

Program Execution Control Statements

if - else Statement

    The if statement evaluates the expression enclosed in parentheses. If the expression evaluates to a nonzero value (true), the statement dependent on the evaluation is executed; otherwise, it is skipped.

syntax  :

    if( condition1 == true )

    {
     if( condition2 == true )

        {
     //do something

        }
     else

        {
    //do something

        }

    }
    else

    {
     //do something

    }

example : 

#include <iostream.h>
int main()
{
    int iCondition=0;
    cout<<"Ener a condition\n";
    cin>>iCondition;
    if( iCondition==1)
        cout<<"You entered 1\n";
    else if( iCondition==2)
        cout<<"You entered 2\n";
    else
    cout<<"Another value\n";
}

Switch Case Statement :

    This control statement allows us to make a decision from a number of choices.

syntax :

    switch (expression)

    {

        case constant 1:

            [Block]

        case constant 2:

            [Block]

        case constant n:

            [Block]

        default :

            [Block]

    }

example :

    #include <iostream.h>
    int main(int argc, char* argv[])
    {
        char cLetter;
        cout<<"Enter a letter\n";
        cin>>cLetter;
        switch (cLetter)
        {
            case 'a':
            case 'e':
            case 'i':
            case 'o':
            case 'u':
                cout<<"The Letter is a Vowel\n";
                break;
            default :
                cout<<"The letter is not a Vowel\n";
                break;
        }
        return 0;
    }

Loops

    while Statement

        The while statement lets you repeat a statement until a specified expression becomes false.

syntax  :

    while ( expression ) statement

example : 

    #include <iostream.h>
    int main()
    {
        int iCount=0;

        while (iCount< 10 ) 
        {
            cout<<iCount++;
        }
    }

    do while Statement

The expression in a do-while statement is evaluated after the body of the loop is executed. Therefore, the body of the loop is always executed at least once.

syntax  :

    do statement while ( expression ) ;

example : 

    int main()
    {
        int iCount=0;
        do

       {
            cout<<iCount++; 
        }while(iCount<10 );
    }

for Statement :

    The for statement lets you repeat a statement or compound statement, a specified number of times.

syntax  :

    for ( init-expression; cond-expression ; loop-expression  ) statement

example : 

    int main()
    {
        for(int iCount=0;iCount<10;iCount++)
        {
            cout<<iCount;
        }
    }