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

Penso che il problema principale sia che la tua variabile globale y1 può essere in conflitto con una funzione definita in math.h (o cmath). Puoi aggirarlo dichiarando le tue variabili a livello locale in main() funzione, piuttosto che come globali. Ciò consente al nome variabile di mascherare la funzione esistente ed evita il conflitto.

EDIT: la soluzione alternativa sarebbe rinominare y1 a qualcos'altro, ad esempio Y1 (maiuscolo).

Ci sono anche un paio di altri problemi nel codice. In due posti che hai cout< invece di cout <<, e ti manca anche un semi-colon.

Answer 2

Aggiornare:

Sembra y0, y1 e yn sono specificato come parte di Posix Il che spiegherebbe perché non lo troverai documentato in C o C ++ Standard:

Le funzioni Y0 (), Y1 () e Yn () devono calcolare le funzioni di Bessel di X del secondo tipo di ordini 0, 1 e N, rispettivamente.

La soluzione a Inquinamento dello spazio dei nomi globali è a Dichiara le tue variabili nel tuo spazio dei nomi.

Originale:

Hai < al posto di << In alcuni dei tuoi cout chiama, ad esempio qui:

cout<"FORMULA L2+H2";
    ^

dovrebbe essere:

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

Anche in clang e gcc, Sto ottenendo un conflitto con il tuo globale y1 e un globale y1 dal cmath Intestazione, il che rende questo:

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

E alcune altre linee si rompono, la mia soluzione era rinominare y1 Ma la soluzione migliore è non usare globali.