Expected primary expression before '.'

Question

#include <iostream>
using std::cout;
using std::endl;

class square {

public:
    double length, width;
    
    square(double length, double width);
    square();
    
    ~square();
    
    double perimeter();
};

double square::perimeter() {
return 2*square.length + 2*square.width;
}

int main() {

square sq(4.0, 4.0);

cout << sq.perimeter() << endl;

return 0;
}

I'm trying to write a simple class program. I am getting the error

in member function 'double square::perimeter()';
.cpp:21: error: expected primary-expression before '.' token
.cpp:21: error: expected primary-expression before '.' token

Does this mean I have to use 2*square::length + 2*square::width?

Answer 1

square is a type, not an object; instead of

return 2*square.length + 2*square.width;

do

return 2*length + 2*width;

(which is implicitly the same as:

return 2*this->length + 2*this->width;

which you may, or ^please may not, prefer for clarity).

2*square::length + 2*square::width would be valid syntax if length and width were

• static members of square, or
• members of some base class square, or
• objects in some namespace square

Answer 2

Yes, the accurate form would be:

return 2*square::length + 2*square::width;

since square is a type, not an object.

In this context, it's the same as:

return 2*this->square::length + 2*this->square::width;

However, since it's the same object and the same type, you can just write:

return 2*this->length + 2*this->width;

or, most simply:

return 2*length + 2*width;