C++ – Expected primary expression before ‘.’


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

class square {

    double length, width;
    square(double length, double width);
    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?

Best Solution

square is a type, not an object; instead of

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


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
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