Why does not execute this linked list code? [closed]

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I don't know why this code doesn't work...

#include <iostream>

using namespace std;

struct Triple {int row, col, value;};

class Matrix;

class MatrixNode 
{
friend class Matrix;
friend istream& operator>>(istream&, Matrix&);
private:
    MatrixNode *down, *right;
    bool head;
    union {
        MatrixNode *next;
        Triple triple;
    };
    MatrixNode(bool, Triple*);
};

MatrixNode::MatrixNode(bool b, Triple* t)
{
    head = b;
    if (b) {right = down = this;}
    else triple = *t;
}

class Matrix {
friend istream& operator>>(istream&, Matrix&);
public:
    ~Matrix();
private:
    MatrixNode *headnode;
};

istream& operator>>(istream& is, Matr开发者_开发知识库ix& matrix)
{
    Triple s;
    cout << "Enter the numbers of row, colume, value" << endl;
    is >> s.row >> s.col >> s.value;

    int p = max(s.row, s.col);

    matrix.headnode = new MatrixNode(false, &s);
    if (p == 0) { matrix.headnode->right = matrix.headnode; return is;}
    MatrixNode **head = new MatrixNode*[p];
    for (int i = 0; i < p; i++)
        head[i] = new MatrixNode(true, 0);
    int currentRow=0;
    MatrixNode *last = head[0];

    for (int i = 0; i < s.value; i++)
    {
        Triple t;
        cout << "Enter the terms" << endl;
        is >> t.row >> t.col >> t.value;
        if (t.row > currentRow){
            last -> right = head[currentRow];
            currentRow = t.row;
            last = head[currentRow];
        }
        last = last -> right = new MatrixNode(false, &t);
        head[t.col]->next = head[t.col]->next->down = last;
    }

    last -> right = head[currentRow];
    for (int i = 0; i < s.col; i++)
        head[i] -> next -> down = head[i];
    for(int i = 0; i < p - 1; i++)
        head[i] -> next = head[i+1];
    head[p-1] -> next = matrix.headnode;
    matrix.headnode -> right = head[0];
    delete [] head;
    return is;
}


int main()
{
    Matrix *a = new Matrix;
    Matrix *b = new Matrix;

    cin >> *a;
    cin >> *b;

}

---

The specific problem is that head[t.col]->next is uninitialized, and you're dereferencing it.

The more general problem is that you've bitten off more than you can chew. You are trying to build something well beyond your ability, and you're trying to do it in one step. Try building a much simpler linked list, say, one without the union, without the operator>>, and with only one dimension, not three. Once you are comfortable with that, work your way up to more advanced structures, in small steps.