Const keywor in c++ 2011

[saneha]

What is the actual purpose of using const keyword tell me in simple words.

[Vuhelper]

To define a variable, data member or member function constant, we use the keyword const. constant data member, member function does not change their value.
For example:
const int A=10;
A=20; //Error
Because A is declare as constant, which value can not be changed.