Question

这是我的程序，它找到一个矩形的区域，周长，如果矩形是方形的。它通过使用两个坐标和建模结构完成所有这些。我对C ++很新，我在这一行上得到一个不熟悉的错误：if（abs（y-a2.y）= abs（a2.x - x））{错误说明：赋值时非左值。< / p>

#include <cstdlib>
#include <iostream>
#include <math.h>

/*
Name: Rectangle
Author: ------
Date: 27/10/14 04:31
Description: A program that finds the area, perimeter, and if a rectangle is square
*/

using namespace std;

class Point
{
private:
    int x, y;

public:

    Point ()
    {
        x = 0;
        y = 0;
    }

    //A four parameter constructor

    Point (int a, int b)
    {
        x = a ;
        y = b ;
    }

    //Setter function

    void setX (int a)
    {
        x = a ;
    }

    void setY (int b)
    {
        y = b ;
    }

    //Accessor functions

    int getX ()
    {
        return x ;
    }

    int getY ()
    {
        return y ;
    }

    //Function to print points

    void printPoint ()
    {
        cout << endl << "(" << x << ", " << y << ")" << endl ;
    }

    //Function to enter new points

    Point newPoint ()
    {
        Point aPoint;
        int a;
        int b;
        cout << "Enter first x coordinate: " ;
        cin >> a ;
        cout << "Enter first y coordinate: " ;
        cin >> b ;
        aPoint.setX(a);
        aPoint.setY(b);
        return aPoint;
    }

    //Function to find area

    int areaA (Point a2)
    {
        int height = y - a2.y ;
        int length = a2.x - x ;
        int area = abs((length * height)) ;
        return area ;
    }

    //Function to find perimeter

    int perimeterA (Point a2)
    {
        int height1 = y - a2.y ;
        int length1 = a2.x - x ;
        int perimeter1 = abs(((length1 + height1) * 2)) ;
        return perimeter1 ;
    }

    //Function to determine shape

    int isSquare (Point a2)
    {
        int square;
        if ( abs(y - a2.y) = abs(a2.x - x) )     //****ERROR ON THIS LINE****
        {
            cout << "It is square" ;
        }

        else
        {
            cout << "It is not square" ;
        }
        return square;
    }
};

Point newPoint();

int main(int argc, char *argv[])
{
    cout << "Enter top left coordinate first and bottom right coordinate second" ;
    cout << endl << endl ;
    Point firstPoint;
    Point secondPoint;
    int areaR;
    int perimeter;
    firstPoint = firstPoint.newPoint();
    secondPoint = secondPoint.newPoint();
    cout << endl ;
    cout << "First point: " ;
    firstPoint.printPoint();
    cout << "Second point: " ;
    secondPoint.printPoint();
    cout << endl ;

    areaR = firstPoint.areaA(secondPoint);
    cout << "Area: " << areaR << endl ;
    perimeter = firstPoint.perimeterA(secondPoint);
    cout << "Perimeter: " << perimeter << endl;

    cout << endl ;
    system("PAUSE");
    return EXIT_SUCCESS;
}

Answer 1

if(abs(y-a2.y) = abs(a2.x - x) )

尝试将abs(a2.x - x)分配给abs(y-a2.y)，这是没有意义的。使用==来比较值。

顺便说一句，isSquare返回一个未初始化的值，这是一个错误。要么返回有意义的函数void。

Answer 2

我在这个错误中没有看到任何奇怪的东西。该行确实尝试将某些内容分配给非左值，正如错误消息所述。在C ++中，等式比较运算符拼写为==。表达式上下文中的单个=是赋值运算符。

还不清楚为什么在包含C库标题时混合两种不同的样式：<cstdlib>和<math.h>。如果您决定加入<cstdlib>，那么包含<cmath>会更有意义。请记住，通过<c...>标头提供的标准库函数应被视为std命名空间的成员。现代C ++中不推荐使用.h版本的heqaders。

奇怪的错误：C ++中赋值的非左值

2 个答案: