Compilation Error: "pointer can only be subtracted from another pointer"

Question

Just learning C++, and I'm enjoying making my first program it's not much, it just solves math problems I'm having some issues with the distance formula as far as I know my logic is right sqrt((x2-x1)+(y2-y1)). However I am getting the error

error C2113: '-' : pointer can only be subtracted from another pointer which is throwing me off.

BONUS question... if anybody could point me to a method of directing users back to the first menu when they have finished with a previous selection that would be cool. I'm assuming some sort of loops but I haven't covered that yet in my C++ class.

Here is the code(sorry if it is messy but I haven't learned proper formatting yet)

#include "stdafx.h"
#include <iostream>
#include <cstdlib>
#include <cmath>
using namespace std;


int selection;
int choice;
int choice2;
double height;
double length;
double a;
double x;
double y;
double const pi = 3.14;
double r;
double m;
double x1;
double x2;
double y1;
double y2;
double distance;

int main(){
cout<<"-------------------------"<<endl;
cout<<"     MATH DESTROYER      "<<endl;
cout<<"-------------------------"<<endl;
cout<<"  1-Geometry Solver      "<<endl;
cout<<"  2-Algebra Solver       "<<endl;
cout<<"  3-"<<endl;
cout<<endl;
cout<<"  Select Option number:  "<<endl;
cin>>selection;
cout<<endl;
cout<<endl;
    switch(selection){
    case 1:
    cout<<"-------------------------"<<endl;
    cout<<"     GEOMETRY SOLVER     ";cout<<endl;
    cout<<endl;
    cout<<" 1-Perimeter of a square "<<endl;
    cout<<" 2-Area of a square      "<<endl;
    cout<<" 3-Perimeter of a rectangle"<<endl;
    cout<<" 4-Area of a rectangle   "<<endl;
    cout<<" 5-Perimeter of a circle "<<endl;
    cout<<" 6-Area of a circle      "<<endl;
    cout<<" Select Option number:   "<<endl;
    cout<<"-------------------------"<<endl;
    cin>>choice;
    cout<<endl;
    cout<<endl;
    switch(choice){
            case 1:
                cout<<"-------------------------"<<endl;
                cout<<"  PERIMITER OF A SQUARE  "<<endl;
                cout<<endl;
                cout<<"Enter Height"<<endl;
                cin>>height;
                cout<<"Enter Length"<<endl;
                cin>>length;
                cout<<"Perimiter of Square ="<<(height*2)+(length*2)<<endl;
                cout<<"-------------------------"<<endl;
                cout<<endl;
                cout<<endl;

                system("pause");
                return 0;

            case 2:
                cout<<"AREA OF A SQUARE"<<endl;
                cout<<endl;
                cout<<"Enter Length"<<endl;
                cin>>length;
                cout<<endl;
                cout<<endl;
                cout<<"FORMULA L^2";
                cout<<endl;
                cout<<endl;
                cout<<"AREA of Square ="<<pow(length,2)<<endl;//(pow)(length,2)= length to the power of 2 or lenght^2
                cout<<endl;
                cout<<endl;

                system("pause");
                return 0;

            case 3:
                cout<<"PERIMITER OF A RECTANGLE"<<endl;
                cout<<endl;
                cout<<"Enter Height"<<endl;
                cin>>height;
                cout<<"Enter Length"<<endl;
                cin>>length;
                cout<<endl;
                cout<<endl;
                cout<"FORMULA L2+H2";
                cout<<endl;
                cout<<endl;
                cout<<"Perimiter of Rectangle ="<<(height*2)+(length*2)<<endl;
                cout<<endl;
                cout<<endl;

                system("pause");
                return 0;

            case 4:
                cout<<"AREA OF A RECTANGLE"<<endl;
                cout<<endl;
                cout<<"Enter Height"<<endl;
                cin>>height;
                cout<<"Enter Length"<<endl;
                cin>>length;
                cout<<endl;
                cout<<endl;
                cout<"FORMULA L2+H2";
                cout<<endl;
                cout<<endl;
                cout<<"Perimiter of Rectangle ="   <<height*length<<endl;
                cout<<endl;
                cout<<endl;

                system("pause");
                return 0;

                case 5:
                cout<<"PERIMITER OF A CIRCLE"<<endl;
                cout<<endl;
                cout<<"Enter Radius"<<endl;
                cin>>r;
                cout<<endl;
                cout<<endl;
                cout<<"FORMULA peremiter=PI X D";
                cout<<endl;
                cout<<endl;
                cout<<"Perimiter of circle ="<<pi*(r*2)<<endl;
                cout<<endl;
                cout<<endl;

                system("pause");
                return 0;

                case 6:
                cout<<"AREA OF A CIRCLE"<<endl;
                cout<<endl;
                cout<<"Enter Radius"<<endl;
                cin>>r;
                cout<<endl;
                cout<<endl;
                cout<<"FORMULA PI X R^2";
                cout<<endl;
                cout<<endl;
                cout<<"Area of Circle ="<<pi*(pow(r,2))<<endl;
                cout<<endl;
                cout<<endl;

                system("pause");
                return 0;

    }
    case 2:
    cout<<"      ALGEBRA MASTER     "
    cout<<"-------------------------"<<endl;
    cout<<"    1-Distance Formula   "<<endl;
    cout<<"    2-Slope              "<<endl;
    cout<<"    3-Pythagorean Theorm "<<endl;
    cout<<"-------------------------"<<endl;
    cout<<endl;
    cout<<"Select Option number:"<<endl;
    cin>>choice2;
        switch(choice2){
            case 1:
                cout<<"Distance Formula"<<endl;
                cout<<endl;
                cout<<"Enter first y point (y1)"<<endl;
                cin>>y1;
                cout<<endl;
                cout<<"Enter second y point (y2)"<<endl;
                cin>>y2;
                cout<<endl;
                cout<<"Enter first x point (x1)"<<endl;
                cin>>x1;
                cout<<endl;
                cout<<"Enter second x point (x2)"<<endl;
                cin>>x2;
                cout<<"D=sqrt (x2-x1)+(y2-y1)";
                cout<<endl;
                cout<<endl;
                cout<<"Distance ="<<sqrt((x2-x1)+(y2-y1))<<endl;
                cout<<endl;
                cout<<endl;

                system("pause");
                return 0;

                case 2:
                cout<<"AREA OF A CIRCLE"<<endl;
                cout<<endl;
                cout<<"Enter Radius"<<endl;
                cin>>r;
                cout<<endl;
                cout<<endl;
                cout<<"FORMULA PI X R^2";
                cout<<endl;
                cout<<endl;
                cout<<"Area of Circle ="<<pi*(pow(r,2))<<endl;
                cout<<endl;
                cout<<endl;

                system("pause");
                return 0;

                case 3:
                cout<<"AREA OF A CIRCLE"<<endl;
                cout<<endl;
                cout<<"Enter Radius"<<endl;
                cin>>r;
                cout<<endl;
                cout<<endl;
                cout<<"FORMULA PI X R^2";
                cout<<endl;
                cout<<endl;
                cout<<"Area of Circle ="<<pi*(pow(r,2))<<endl;
                cout<<endl;
                cout<<endl;

                system("pause");
                return 0;

    }


    }
}

Answer 1

Ich denke, das Hauptproblem ist, dass Ihre globale Variable y1 kann mit einer in definierten Funktion in widersprüchlich sein math.h (oder cmath). Sie können das umgehen, indem Sie Ihre Variablen lokal in der deklarieren main() Funktionen und nicht als Global. Dadurch kann der variable Name die vorhandene Funktion maskieren und den Konflikt vermeidet.

Bearbeiten: Die alternative Lösung wäre, umzubenennen y1 zu etwas anderem, zB Y1 (oberer Fall).

Es gibt auch einige andere Probleme im Code. An zwei Orten haben Sie cout< Anstatt von cout <<, Und Sie vermissen auch ein Semikolon.

Answer 2

Aktualisieren:

Es sieht aus wie y0, y1 und yn sind als Teil von POSIX festgelegt Das würde erklären, warum Sie dies nicht in der dokumentiert finden werden C oder C ++ Standards:

Die Funktionen von Y0 (), Y1 () und YN () berechnen die Bessel -Funktionen der zweiten Art von Ordnungen 0, 1 bzw. n.

Die Lösung für Globaler Namespace -Verschmutzung ist zu Deklarieren Sie Ihre Variablen in Ihrem eigenen Namespace.

Original:

Du hast < anstelle von << in einigen von Ihnen cout Anrufe zum Beispiel hier:

cout<"FORMULA L2+H2";
    ^

sollte sein:

cout<<"FORMULA L2+H2";
    ^^

Auch in clang und gcc, Ich bekomme einen Konflikt mit Ihrem Global y1 und eine globale y1 von dem cmath Header, was das macht:

cout<<"Distance ="<<sqrt((x2-x1)+(y2-y1))<<endl;
                                     ^^

und ein paar andere Linien brechen, meine Lösung war es, umzubenennen y1 Die bessere Lösung besteht jedoch darin, keine Globale zu verwenden.