C++結構不編譯...未正確初始化？不正確使用它們？

Question

我使用嵌套的結構/結構，經過幾個小時的僞代碼和嘗試，我提出的最終結果不起作用或不能編譯。

我想採取兩個向量A和B，並將它們相互比較。我設置了嵌套結構來讀取矢量的開始和結束點以及矢量結構本身。所以我想我可能會在下面做一些錯誤，但我被卡住了。

#include <iostream> 
    #include <cmath> 
    #include <string> 

    using namespace std; 
struct Point // Reads in three coordinates for point to make a three dimensional vector 
{ 
    double x; 
    double y; 
    double z; 
}; 
struct MathVector // Struct for the start and end point of each vector. 
{ 
    Point start; 
    Point end; 
}; 
Point ReadPoint() 
{ 
    Point pt; // Letter distinguishes between vector A and vector B, or "letterA" and "letterB" 
    double x, y, z; 

    cout << "Please input the x-coordinate: " << endl; 
    cin >> pt.x; 
    cout << "Please input the y-coordinate: " << endl; 
    cin >> pt.y; 
    cout << "Please input the z-coordinate: " << endl; 
    cin >> pt.z; 

    return pt; 
} 
void DotProduct (MathVector letterA, MathVector letterB, double& a_times_b) //formula to compute orthogonality 
{ 
    a_times_b = (letterA.end.x - letterA.start.x)*(letterB.end.x - letterB.start.x) + (letterA.end.y - letterA.start.y)*(letterB.end.y - letterB.start.y) + (letterA.end.z - letterA.start.z)*(letterB.end.z - letterB.start.z); 
} 
int main() 
{ 
    MathVector letterA; 
    MathVector letterB; 
    double a_times_b; 

    letterA = ReadPoint(); 
    letterB = ReadPoint(); 

    DotProduct (letterA, letterB, a_times_b); 

    cout << "The vector " << letterA << " compared with " << letterB << " "; 
    if (a_times_b == 0) 
     cout << "is orthoganal." << endl; 
    else 
     cout << "is not orthoganal." << endl; 

    return 0; 
} 

Answer 1

的一個問題是你的ReadPoint返回類型爲Point，但你回來的MathVector一個實例。此外，您將輸入讀入最終忽略的變量。

你應該寫ReadPoint爲：

Point ReadPoint() 
{ 
    Point p; 
    cout << "Please input the x-coordinate: " << endl; 
    cin >> p.x; 
    cout << "Please input the y-coordinate: " << endl; 
    cin >> p.y; 
    cout << "Please input the z-coordinate: " << endl; 
    cin >> p.z; 
    return p; 
} 

或者好一點的版本：

Point ReadPoint() 
{ 
    Point p; 
    cout << "Please enter point-coordinate : " << endl; 
    cin >> p.x >> p.y >> p.z; //example input : 1 2 3 
    return p; 
} 

或者說，仍然是越多越好，過載>>操作爲：

std::istream & operator>>(std::istream & in, Point & p) 
{ 
    cout << "Please enter point-coordinate : " << endl; 
    return cin >> p.x >> p.y >> p.z; //example input : 1 2 3 
} 

//Use this as 
Point pointA, pointB; 
cin >> pointA >> pointB; 

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Answer 2

1. ReadPoint返回類型MathVector，而不是點的信
2. 您還沒有重載操作< <告訴它如何處理MathVector對象

Answer 3

Point ReadPoint() 
{ 
    MathVector letter; // Letter distinguishes between vector A and vector B, or "letterA" and "letterB" 
    double x, y, z; 

    cout << "Please input the x-coordinate: " << endl; 
    cin >> x; 
    cout << "Please input the y-coordinate: " << endl; 
    cin >> y; 
    cout << "Please input the z-coordinate: " << endl; 
    cin >> z; 

    return letter; 

}

你沒有解釋什麼是你正在試圖做的還是你有什麼錯誤，但是這個代碼使得沒有感。您有三個變量，x,y和z。你用你從用戶那裏得到的值填充它們。然後你不會對這些變量做任何事情，並且返回由默認構造函數創建的MathVector，即使你說你要返回Point。這沒什麼意義。

Answer 4

letterA和letterB的類型MathVector

MathVector letterA; 
     MathVector letterB; 
     double a_times_b; 

     letterA = ReadPoint(); 
     letterB = ReadPoint(); 

你應該建立另一種方法來讀取Mathvector ..作爲你與Point做。

和方法ReadPoint

返回類型必須是點..如果你閱讀點然後在這裏做計算創建對象MathVector go tet startpoint和endpoint格式。

Answer 5

'operator ='錯誤的匹配意味着沒有將MathVector分配給Point的函數。您正在調用ReadPoint（），它將返回一個Point並嘗試將返回的值分配給MathVector類型的變量。編譯器不能自動創建「轉換」功能。你必須自己提供一個。也許你的意思是

letterA.start = ReadPoint(); 
letterA.end = ReadPoint();