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Mmm, now would be an excellent time to try out the debugger.
See if you can spot the error. Will do you good practice.

By calling appropriate member functions on the objects! You know the Rectangle is supposed to work, right?

That is normal output. Nothing wrong there.
You should be looking at the black console window that pops up.



What does redefine mean in this context?

When I ran your corrected example, I got

The length entered is invalid and has been set to 1.00The width entered is inval
id and has been set to 1.00Length: 1Width: 1Area: 1Perimeter: 4Length:...

Don't worry about it. I did not put much thought into that code.
It was a simple example, not one meant to be correct in any way (for example, why should the result be a double if both parameters...

The only problems I find are

cout<< "Area: " << area;
cout<< "Perimeter: " << perimeter;

You don't have member variables or local variables named area and perimeter. Presumably you...

#include <iostream>

class Rectangle
{
public:
Rectangle(double area, double length);
double CalcPerimeter() const;
private:
double m_length, m_area;
};

You told the compiler that the printData function was global in your .cpp file:

void printData()

should be

void Rectangle::printData()

As for the calc functions, you forgot to add...

If, in your class definition (as it's called; weird, I know), you have:

Rectangle (double length);

Then, in your accompanying .cpp file, you must have (note that the type is there)
...