Why is this code showing segmentation fault (core dumped ) ?

$user ./a.out < input.txt

2 0 7 0 9 0 4 0 6     
0 4 0 2 6 7 0 5 3
5 0 0 3 8 4 0 0 0
6 0 0 5 2 8 3 0 7
8 2 5 0 3 1 0 0 9
0 0 1 9 4 6 0 2 0
4 0 2 6 1 9 7 0 8
9 1 3 8 0 0 0 0 4
7 0 0 0 5 3 1 9 2

0 0 5 7 1 0 6 8 2
0 3 6 0 4 0 0 7 5
7 0 0 5 8 6 3 4 9
9 8 4 0 5 7 2 0 0
1 5 0 0 0 0 7 9 8
6 7 2 8 0 0 0 0 4
0 6 8 2 0 9 0 1 0
3 4 9 1 0 0 8 2 0
0 1 7 0 3 0 9 0 6

3 0 0 2 0 0 0 0 0
0 0 0 1 0 7 0 0 0
7 0 6 0 3 0 5 0 0
0 7 0 0 0 9 0 8 0
9 0 0 0 2 0 0 0 4
0 1 0 8 0 0 0 5 0
0 0 9 0 4 0 3 0 1
0 0 0 7 0 2 0 0 0
0 0 0 0 0 8 0 0 6

0 0 0 0 0 3 0 1 7
0 1 5 0 0 9 0 0 8
0 6 0 0 0 0 0 0 0
1 0 0 0 0 7 0 0 0
0 0 9 0 0 0 2 0 0 
0 0 0 5 0 0 0 0 4
0 0 0 0 0 0 0 2 0
5 0 0 6 0 0 3 4 0 
3 4 0 2 0 0 0 0 0

//where the debugger returns the error 
bool mySudoku::CheckRow(int row, int number){ //check row for user inputted number 
    	for(int i=0; i< SIZE; i++)            //return true if number is found
	{                                     //false if not
            if(Data[row][i] == number)
            {
				return true;
            }
	}
    return false;
}

#include "mySudoku.h"
#include <cstdlib>
#include <iostream> 

using namespace std;

mySudoku::mySudoku(){ //default constructor 
    for(int row=0; row < SIZE; row++)
    {
        for(int col=0; col < SIZE; col++)
        {
            Data[row][col] = 0;
        }
    }
    //initalize Array's data to all 0's
}

mySudoku::mySudoku(int anArray[][SIZE]){ //alternate constructor 
    for(int row=0; row < SIZE; row++)
    {
        for(int col=0; col < SIZE; col++)
        {
            Data[row][col] = anArray[row][col];
        }
    }
}

mySudoku::mySudoku(const mySudoku& orig){ //copy constructor
    
}

mySudoku::~mySudoku(){
    //destructor
}

void mySudoku::ReadPuzzle(){  //read the puzzle 
    cout << "Please input values for grid of the puzzle" <<endl;
    for(int row=0;row< SIZE; row++)
    {
        for(int col=0; col< SIZE; col++)
        {
			cout << "Row " << row+1 << " Col " << col+1 << endl;
            cin >> Data[row][col];
        }
    }
    cout << "you have completed inputting values for the grid!" << endl;
}

void mySudoku::PrintPuzzle(){ //prints the puzzle 
    for(int row=0; row < SIZE; row++)
    {
        for(int col=0; col < SIZE; col++)
        {
            cout << Data[row][col] << " ";
        }
        
        cout << endl;
    }
}

bool mySudoku::CheckCol(int col, int number){  //check col for user inputted number
	for(int i=0;i< SIZE; i++)               //return true if number is found 
	{                                       //false if not 
            if(Data[i][col] == number)
            {
                return true;
            }
	}
    return false;
}

bool mySudoku::CheckRow(int row, int number){ //check row for user inputted number 
    	for(int i=0; i< SIZE; i++)            //return true if number is found
	{                                     //false if not
            if(Data[row][i] == number)
            {
				return true;
            }
	}
    return false;
}

bool mySudoku::CheckSubBox(int row, int col, int number){ //check sub box for user inputted number 
    int startIndexRow = row-row%3;					      //return true if number is found
    int startIndexCol = col-col%3;						  //false if not
    
    for(int i=0; i<3; i++)
    {
        for(int j=0; j<3; j++)
        {
            if(Data[startIndexRow+i][startIndexCol+j] == number)
            {
                return true; 
            }
        }
    }
    return false; 
}

bool mySudoku::CheckForUnassigned() //checks for unassigned values 
{									//which are denoted by a zero 
	for(int i=0; i<SIZE;i++)		//return true if unassigned value exist 
	{								//false if not 
		for(int j=0; j<SIZE; j++)
		{
			if(Data[i][j] == 0)
			{
				return false;
			}
		}
	}
	return true;

}

int mySudoku::SolvePuzzle(int iterations){ //solves the puzzle on two conditions 
int counter=0;							   //by a certain number of iterations 
while(iterations != 0)					   //or until convergence 
{
	for(int i=0; i < SIZE; i++) 
	{
		for(int j=0; j < SIZE; j++) 
		{
			if(Data[i][j]==0)
			{
				int ansCount=0;
				int ans =0;
				for(int k=1; k < SIZE+1; k++)
				{
					if((CheckRow(i,k)==false)&&(CheckCol(j,k)==false)&&(CheckSubBox(i,j,k)==false))
					{
						ansCount++;
						ans = k;
					}
					
				}
				if(ansCount == 1)
				{
					Data[i][j] = ans;
				}
			}

		}
	}
	if(iterations > 0)
	{
		iterations--;
	}
	else if((iterations < 0) && (CheckForUnassigned()==true))
	{
		counter++; 
		return counter; 
	}
	else if((iterations < 0) && (CheckForUnassigned()==false))
	{
		counter++;
		SolvePuzzle(iterations);
	}

	counter++;

}
 return counter;

}

#include <cstdlib>
#include <iostream>
#include "mySudoku.h"

using namespace std;

/*
 * 
 */
int main(int argc, char** argv) {
    //initialize test array
    int testArray[9][9]; 
    
    //populate array
    for(int row=0; row<9; row++)
    {
        for(int col=0; col<9; col++)
        {
            testArray[row][col] = 0;
        }
    }
    
    
    //define object mySudoku 
    mySudoku Stest1;
    mySudoku Stest2(testArray);
    
    
    Stest1.ReadPuzzle();    //read puzzle 
    Stest1.CheckCol(1,3);  //check column 
    Stest1.CheckRow(1,3);  //check row
    Stest1.CheckSubBox(4,4,5); //check 3x3 subbox
    cout << " iteration: " << Stest1.SolvePuzzle(-1) << endl;  //solves puzzle test 
    Stest1.PrintPuzzle();   // print puzzle 
    cout << "\n";
    Stest2.PrintPuzzle();
   
    return 0;
}

#ifndef MYSUDOKU_H
#define	MYSUDOKU_H

const int SIZE(9); //constant 

class mySudoku {
public:
    mySudoku(); //default constructor 
    mySudoku(int anArray[][SIZE]); //alternate constructor 
    mySudoku(const mySudoku& orig);//copy constructor 

    //functions 
    void ReadPuzzle(); 
    void PrintPuzzle(); 
    int SolvePuzzle(int iterations);
    bool CheckRow(int row, int number);
    bool CheckCol(int col, int number);
    bool CheckSubBox(int row, int col, int number);
	bool CheckForUnassigned();
    
    virtual ~mySudoku();
private:
    int Data[SIZE][SIZE];
};

#endif	/* MYSUDOKU_H */