Question

I have to create a class Histogram and make operations on this class. The input can be one dimensional array or a two dimensional array. The problem appears when i convert the array into a matrix. This what i have tried so far. The error is <Unable to read memory>

histrogram.h

#ifndef HISTOGRAM_H
#define HISTOGRAM_H
#include<iostream>
class Histogram
{
private:
    int** matrix;
    int lines;
    void SortMatrix();
public:
    Histogram(){ }
    Histogram(int elements[], int elementsNr);
    Histogram(int** m, int l);
    void Print();
};
#endif

historgram.cpp

#include"histogram.h"
using namespace std;
Histogram::Histogram(int** m, int l)
{
    matrix=m;
    lines=l;
    SortMatrix();
}

Histogram::Histogram(int elements[], int elementsNr)
{
    lines=0;
    //initialize matrix : elementrNr lines and 2 columns
    int** matrix=new int*[elementsNr];
    for(int i=0;i<elementsNr;i++)
    {
        matrix[i]=new int[2];
        matrix[i][0]=INT_MIN;
        matrix[i][1]=INT_MIN;
    }
    //search each element from the array in the matrix
    bool found=false;
    for(int i=0;i<elementsNr;i++)
    {
        found=false;
        for(int j=0;j<elementsNr;j++)
        {
            //the element was found in the matrix ( on the first column )
            if(matrix[j][0] == elements[i])
            {
                matrix[j][1]++;
                found=true;
                break;
            }
        }
        if(!found)
        {
            matrix[lines][0]=elements[i];
            matrix[lines][1]=1;
            lines++;
        }
    }
    SortMatrix();
}
void Histogram::SortMatrix()
{
    bool flag=true;
    int temp;
    for(int i=0;(i<lines) && flag;i++)
    {
        flag=false;
        if(matrix[i+1][0]>matrix[i][0])
        {
            temp=matrix[i][0];
            matrix[i][0]=matrix[i+1][0];
            matrix[i+1][0]=temp;
            flag=true;
        }
    }
}
void Histogram::Print()
{

    for(int i=0;i<lines;i++)
    {
        cout<<matrix[i][0]<<" : " <<matrix[i][1]<<endl;
    }

}

main.cpp

#include"histogram.h"
#include<iostream>
using namespace std;

int main()
{
    int arr[]={6,7,3,1,3,2,4,4,7,5,1,1,5,6,6,4,5};
    Histogram h(arr,17);
    h.Print();
}

Answer 1

Here

int** matrix=new int*[elementsNr];

replace with

matrix=new int*[elementsNr];

becausematrix is already a member variable. You are creating a new temporary variable double pointer named matrix and allocating memory to it rather than your member variable matrix