function to calculate the Circumference of a circle

here's my function

double Circle::calcPerimeter() const
{
return perimeter = 2 * radius * 3.1425;
}

on visual c++ i get this error....

error C2166: l-value specifies const object

any ideas......?

Maybe this'll work

double Circle::calcPerimeter()
{
return 2 * radius * 3.1425;
}

its for an assignment..which the requires the function to be a const....using the variable name perimeter.

what about:

const double Circle::calcPerimeter()
{
return perimeter = 2 * radius * 3.1425;
}