Constant Member Function in C++

What is difference between constructor and destructor

Constant members in C++

Member of class can be declared as constants Constant members are of  2 types. Constant data member Constant member function  

Constant data member

The value of constant data member has never changed. Constant data member must be initialized using constructor list It is used to defined read only property of object  

Constant Member Function Syntax

const data type   datamember-name syntax of init constant data members using construct list constructor-name(): constant-datamember(value,constant-datamember(value)---- { statements; }

//wap to find area of circle

Example # include <iostream.h> class circle { float r; const float pi; public : circle() : pi(3.147) { r=1.5; } void find_area() { float area=pi*r*r; cout<<”\n Area is”<<area; }}; void main() { circle circle1;              // create a object by calling constructor circle1.find_area(); }     Constant member function Example

//Finding simple interest :

#inlude<iostream.h> #include<conio.h> class simple_interest { float amt; int time; const float rate; public : simple_interest(float a, int l, float r): rate(r) { amt=a; time=t; } float find_interest() { float si=(amt * rate *time)/100; cout<<”\n simple interest”<<si; } } void main() { simple_interest_cust1(5000,12,1.5); simple_interest_cust2(7000,24,2.5); cust1.find_intrest (); cust2.find_intrest (); }    

Constant member function in C++

Constant member function is an accessory function which cannot modifying values of data members. It perform constant operation.  

syntax :

<return type> function-name(<parameters>) constant { statements; }  

Constant member function Example

# incude<iostream.h> class account { int accno; char name[10]; char name[10];                 //   private data float balance; public : void read(); //modifier(it modifying) void print_details() const; }; void accout:: read() { cout<<”\n input account no”; cin>>accno; cout<<”\n input customer name”; cin>>name; cout<<”\n input balance”; cin>>balance; } void account :: deposit(float tamt) { balance=balance+tamt; } void accout :: print_details() const { cout<<”\n account no”<<accno; count<<”\n customer Name”<<Name1; cout<<”\n balance”<<balance; } void main() { account acc1; acc1.read(); acc1.deposit(3000); acc1.print_details(); } o/p : input account no