C ++错误：“ double”之前的预期主表达式

Question

I need to write a class program that calculates the distance between two points - Point.cpp, and another class program that calls my Point.cpp program to calculate the length(basically distance from Point.cpp) and slope between two points - LineSegment.cpp. I tested my Point.cpp separately and it runs fine. But when I run everything together (in conjunction with the LineSegment.cpp), I get the following error message:

LineSegment.cpp: In member function ‘void LineSegment::setEnd1(Point)’:
LineSegment.cpp:31: error: expected primary-expression before ‘double’
LineSegment.cpp:32: error: expected primary-expression before ‘double’
LineSegment.cpp: In member function ‘void LineSegment::setEnd2(Point)’:
LineSegment.cpp:37: error: expected primary-expression before ‘double’
LineSegment.cpp:38: error: expected primary-expression before ‘double’

My codes are below. I have marked the 4 lines that the error message refers to with a comment (everytime I posted my code with line numbers I received a suggested edit to take the line numbers out, so I did not include line numbers this time).

My guess is that I am calling the functions from Point.cpp incorrectly, but my textbook does not tell me how to call functions from a nested class. Any guidance would be appreciated. Thank you all for your time!

LineSegment.hpp

#ifndef LINESEGMENT_HPP
#define LINESEGMENT_HPP
#include "Point.hpp"

class LineSegment {
private:
   Point p1;
   Point p2;

public:
   LineSegment(Point, Point);
   void setEnd1(Point p1);
   void setEnd2(Point p2);
   Point getEnd1();
   Point getEnd2();
   double length();
   double slope();
};
#endif

LineSegment.cpp

#include <iostream>
#include <cmath>
#include "LineSegment.hpp"

//constructor
LineSegment::LineSegment(Point p1, Point p2) {
   setEnd1(p1);
   setEnd2(p2);
}

//set and get points
void LineSegment::setEnd1(Point p1) {
   p1.setXCoord(double);       // <-- error
   p1.setYCoord(double);       // <-- error
   setEnd1(p1);
}

void LineSegment::setEnd2(Point p2) {
   p2.setXCoord(double);       // <-- error
   p2.setYCoord(double);       // <-- error
   setEnd2(p2);
}

Point LineSegment::getEnd1() {
   return p1;
}

Point LineSegment::getEnd2() {
   return p2;
}

//calculations
double LineSegment::length() {
   return p1.distanceTo(p2);
}

double LineSegment::slope() {
   return(p2.getYCoord()-p1.getYCoord())/p2.getXCoord()-p1.getXCoord();
}

Point.hpp

#ifndef POINT_HPP
#define POINT_HPP
class Point {
private:
   double xCoord;
   double yCoord;

public:
   Point();
   Point(double x1, double y1);
   void setXCoord(double x1);
   void setYCoord(double y1);
   double getXCoord();
   double getYCoord();
   double distanceTo(const Point&);
};
#endif

Point.cpp

#include <cmath>
#include <iostream>
#include "Point.hpp"

//default constructor
Point::Point() {
   xCoord = 0.0;
   yCoord = 0.0;
}

//constructor
Point::Point(double x, double y) {
   xCoord = x;
   yCoord = y;
}

//get and set functions
void Point::setXCoord(double x) {
   xCoord = x;
}

void Point::setYCoord(double y) {
  yCoord = y;
}

double Point::getXCoord() {
   return xCoord;
}

double Point::getYCoord() {
   return yCoord;
}

// calculate distance
double Point::distanceTo(const Point& p2) {
  double dx = p2.xCoord - xCoord;
  double dy = p2.yCoord - yCoord;
  return sqrt(dx * dx + dy * dy);
}

Answer 1

 p2.setXCoord(double); // <-- error p2.setYCoord(double); // <-- error 

double is a type, not a valid actual parameter name.

Call those functions with a value or a variable that is double or at least convertible to double .

Answer 2

double is a reserved keyword for the double type, it can't be passed to a function as an argument, you need to forward the actual values from the Point type.

void LineSegment::setEnd1(Point p1) {
   p1.setXCoord(p1.getXCoord());   
   p1.setYCoord(p1.getYCoord());   
}

Answer 3

double is a type specifier not an object. And why does for example setEnd1 call itself?

It seems you mean the following

//set and get points
void LineSegment::setEnd1(Point p1) {
   this->p1.setXCoord(p1.getXCoord());       // <-- error
   this->p1.setYCoord(pq.getYCoord());       // <-- error
}

void LineSegment::setEnd2(Point p2) {
   this->p2.setXCoord(p2.getXCoord());       // <-- error
   this->p2.setYCoord(p2.getXCoord());       // <-- error
}

You could write even simpler

//set and get points
void LineSegment::setEnd1(Point p1) {
   this->p1 = p1;
}

void LineSegment::setEnd2(Point p2) {
   this->p2 = p2;
}

And at least in the class Point all these member functions should be declared with qualifier const

double getXCoord() const;
double getYCoord() const;
double distanceTo(const Point&) const;

Answer 4

void LineSegment::setEnd1(Point p1) {
   p1.setXCoord(double);       // <-- error
   p1.setYCoord(double);       // <-- error
   setEnd1(p1);
}

LineSegment's set functions each take one argument of class Point. So when you give it a variable of type Point, you must save it as point.

void Point::setXCoord(double x) {
   xCoord = x;
}

This bit of your code is the template for what you want to do. Instead of type double, you want type Point for p1 and whatever the destination is called.