isSquare method
Implementation
bool isSquare() {
return radius4XS == 0.0 &&
radius3XS == 0.0 &&
radius2XS == 0.0 &&
radiusXS == 0.0 &&
radiusS == 0.0 &&
radiusM == 0.0 &&
radiusL == 0.0 &&
radius3XL == 0.0;
}