Question

I am having trouble understanding how this code is able to use the contents of the header file. Can someone please provide comments in the main code to describe what is happening? (especially on the bool isNumber)

THE MAIN CODE:

#include<bits/stdc++.h>
#include "MyCartesianPoint.h"
#include <math.h>
#include <iostream>

using namespace std;

bool isNumber(string s)
{
   if(!isdigit (s[0]))
   {
       if(s[0] != '-')
       return false;
      
       else if(s.length() == 1)
       return false;
   }
  
   for (int i = 1; i < s.length(); i++)
   if (isdigit(s[i]) == false)
  
   return false;
   return true;

}

int main()
{
   string x, y;
   int X, Y;

CartesianPoint::SetLimit(10);
vector<CartesianPoint> v;
CartesianPoint origin(0,0);
v.push_back(origin);
cout << "You will be travelling from (0, 0) to (10, 10) in as many steps as you like. Enter (10, 10) to end.\n";
  
do
{
   cout << "Move from " << v.back().ToString() << " to where? ";
   CartesianPoint p;
  
       cout << "\nX:";
   while(true)
   {
       cin >> x;
         
       if(isNumber(x))
       {
               try
           {
               X = stoi(x);
                   p.SetX(X);
                   break;
           }
               catch(exception& e)
               {
                   //if there is an exception
                   cout << "* Invalid input. " << e.what() << " ";
               }
           }
         
       else
       cout << "* Invalid input. Please try again and enter a numeric value. ";
   }
  
   cout << "Y:";
     
   while(true)
   {
       cin >> y;
         
       if(isNumber(y))
       {
           try
           {
                   Y = stoi(y);
                   p.SetY(Y);
                   break;
               }
              
               catch(exception& e)
               {
                   // If there is an exception:
                   cout << "* Invalid input. " << e.what() << " ";
               }
           }
          
       else
       cout << "* Invalid input. Please try again and enter a numeric value. ";
   }
  
// Insert into v:
v.push_back(p);
  
}

while(X != 10 || Y != 10);
  
double dist = 0;
cout << "DEBUGGING ONLY:\n";
for(int i = 0; i < v.size() - 1; i++)
{
   double d = v[i].GetDistanceTo(v[i + 1]);
   cout << v[i].ToString() << " -> " << v[i + 1].ToString() << ": " << fixed << setprecision(2) << d << endl;
  
   dist += d;
}
cout << "\nFINAL OUTPUT:\n";
cout << "The total distance between " << v.size() << " points is " << fixed << setprecision(2) << dist << ".";
}

THE HEADER FILE:

#ifndef MY_CARTESIAN_POINT_H

#define MY_CARTESIAN_POINT_H

#include <iostream>        // cin, cout
#include <sstream>            // stringstream
#include <cmath>           // sqrt()
#include <limits>           // INT_MAX
#include <stdexcept>       // out_of_range

using namespace std;

// class declaration section
class CartesianPoint
{
public:
/* Constructor: Used to initialize objects */
CartesianPoint(int x = 1, int y = 1) { SetPoint(x, y); }
  
/* Accessors: Used to query the state of the object */
   int GetX() const { return myX; }
   int GetY() const { return myY; }
  
// get the distance between this point and a second point
    double GetDistanceTo(CartesianPoint pointTo) const;
    string ToString() const; // convert the obj to a string.  
  
/* Mutators: Used to change the state of the object */
   void SetX(int x) { myX = validateCoordinateValue(x); }
   void SetY(int y) { myY = validateCoordinateValue(y); }
   void SetPoint(int x, int y) { SetX(x); SetY(y); }  
  
/* Static methods:
       - Can be used to access/mutate static data members
       - Can be called without an object
   */
   // get the limit
   static int GetLimit() { return sharedLimit; }
   // set the limit
   static void SetLimit(int limit) { sharedLimit = abs(limit); }

/* Friend Functions: Nonmember functions/methods that are granted the same
        privileges as member methods
*/
// TO-DO: Add ReadCartesianPoint() to the friends list
   
     
private:
// private data members for the dimensions of the point
int myX; // x-axis (horizontal) value
int myY; // y-axis (vertical) value
  
// Static data-member: Shared among all objects of this class.
   static int sharedLimit;
  
// Helper method for validation
int validateCoordinateValue(int value) const;

};

// Class definition section

/** sharedLimit static data-member for CartesianPoint class
*   Used to validate the x and y coordinate values.
*/
int CartesianPoint::sharedLimit = INT_MAX;

/** GetDistanceTo Method for CartesianPoint class
*   Determines the distance between this point and a second point.
*   @param   pointTo: CartesianPoint
*   @return   the distance as a double
*/
double CartesianPoint::GetDistanceTo(CartesianPoint pointTo) const
{
int xDelta = pointTo.myX - myX; // difference between x values
int yDelta = pointTo.myY - myY; // difference between y values
// return the formula (based on Pythagorean theorem)
   return sqrt((xDelta * xDelta) + (yDelta * yDelta));
}

/** ToString Method for CartesianPoint class
*   Converts the obj to a string.
*   @return   the obj state as a string
*/
string CartesianPoint::ToString() const
{
   // declare a stringstream object
   stringstream strOut;
   // build the string
   strOut << "(" << myX << ", " << myY << ")";
   // return the string
   return strOut.str();
}

/** validateCoordinateValue Method for CartesianPoint class
*   Determines if the parameter is valid for a coordinate value.
*   @param   value (int)
*   @return   the parameter if valid
*   @throws an out_of_range exception if not in range
*/

int CartesianPoint::validateCoordinateValue(int value) const
{
   // if the parameter is within the limits
   if((value < -sharedLimit || value > sharedLimit))
   {
       // throw an exception
       throw out_of_range( "Parameter (" + to_string(value) + ") must be between "
           + to_string(-sharedLimit) + " and " + to_string(sharedLimit) + ".");
   }
  
   return value;
}

#endif

Answer 1

Explanation with comment: The input number of X and Y is taken as string and passed to isNumber function to check if it is valid number or not. This is how it works:

bool isNumber(string s)
{

   // since number can be negative check if first digit is negative sign "-"
if(!isdigit (s[0]))
{

   // first digit is neither number nor '-1' which is not valid so return false
if(s[0] != '-')
return false;

// first symbol is '-' means negative number
// But if length is 1 it means only '-' in input which is not valid
else if(s.length() == 1)
return false;
}
//check for remaining chracters if they are valid
for (int i = 1; i < s.length(); i++)
// if any of input digit is not a number return false
if (isdigit(s[i]) == false)
       return false;

// all conditions satisfied so return true.
return true;
}

How does file inclusion works?

#include "MyCartesianPoint.h"

This line means that compiler search for file name "MyCartesianPoint.h" in current directory as well as specified list of directories in include path

Had it been written like #include <MyCartesianPoint.h> It would have searched for specified list by compiler only. Not even the current directory. That's why #include <bits/stdc++.h> is written to save searching time. Even writing #include "bits/stdc++.h" will work. Try this to see.

Now in header file "MyCartesianPoint.h"

#ifndef MY_CARTESIAN_POINT_H
#define MY_CARTESIAN_POINT_H

and at last

#endif is used.

This are also known as guards to avoid multiple declaration error. Understand the basics first. : On finding #include "MyCartesianPoint.h" the compiler expands it into the oringal file. Now here only one header file is used so treat it simply as if both have been written in same file. Now but why do we need guards? Here even if you remove them it would cause no error as only one header file is used. But it there was one more file say hello.cpp which was included in The main code and hello.cpp also included "MyCartesianPoint.h" then compiler would give error if there are no guards. Reason=> See when #include "MyCartesianPoint.h" included all functions were expanded in main file. When hello.cpp was included it's function were also included. Now hello.cpp contained"MyCartesianPoint.h" so it had the functions of "MyCartesianPoint.h" already in it and they were also added to main. Now main contains each function of "MyCartesianPoint.h" twice. And what happens if anything is more than once?

Say int a= 5; int a=5; ?

It will give multiple declaration error.

So guards avoid this. They cause inclusion only once.

#ifndef MY_CARTESIAN_POINT_H
#define MY_CARTESIAN_POINT_H

On encountering first time MY_CARTESIAN_POINT_H is not defined so it defines it. But when hello.cpp causes "MyCartesianPoint.h" to get included again MY_CARTESIAN_POINT_H is defined so it does not get included. (ifndef means if not defined)

======

if(isNumber(x)) => check if input is valid number

X = stoi(x); => stoi() converts string into integer

v[i].GetDistanceTo(v[i + 1]); =>v[i] is object of Cartesian Point class. It has function GetDistanceTo() which takes another point as input which is v[i+1].

Until we reach 10,10 do while loop keeps on working.Each path from and to points are pushed in vector v. Then we calculate distance for each path and print it. And in whole process header file is used just like if it is declared in main code itself.

Please comment if you still have any doubts.