CODEWITHSUNDEEP
c#
tomdavies
tomdavies

Reputation: 1976

What's wrong with this code? Cannot apply indexing with [] to an expression of type

I'm writing a small console app. I have no idea what's wrong...

namespace Mtrx
{
    class Mtrx
    {
        private double[,] _sqMtrx;
        private double _mtrxSize { get; set; }

        public Mtrx(int i)
        {

            if (i <= 0)
                throw new FormatException();
            else
                this._sqMtrx = new double[i, i];
            _mtrxSize = i;
        }

        public static Mtrx operator +(Mtrx m1, Mtrx m2)
        {
            if (m1._mtrxSize == m2._mtrxSize)
            {
                for (int i = 1; i <= m1._mtrxSize; i++)
                {
                    for (int j = 1; j <= m1._mtrxSize; j++)
                    {
                        return m1[i, j] == m1[i, j] + m2[i, j];
                    }
                }
            }
        }
    }
}

and I get: Cannot apply indexing with [] to an expression of type 'Mtrx.Mtrx'

Upvotes: 0

Views: 962

Answers (3)

Charles Bretana
Charles Bretana

Reputation: 146469

Shouldn't the innermost line in your nested for loops be referencing the array, not the mr1, mr2 variables?

    public static Mtrx operator +(Mtrx m1, Mtrx m2)
    {
        if (m1._mtrxSize == m2._mtrxSize)
        {
            var outVal = new Mtrx(m1._mtrxSize)

            for (int i = 1; i <= m1._mtrxSize; i++)
                for (int j = 1; j <= m1._mtrxSize; j++)
                    outVal._sqMtrx[i,j] = m1._sqMtrx[i, j] + m2._sqMtrx[i, j];

            return outVal;
        }
    }

If you want to use indexing syntax on the class itself, then you must add an indexer.... 

class Mtrx
{
    private double[,] _sqMtrx;
    private int _mtrxSize { get; set; }

    public Mtrx(int i)
    {

        if (i <= 0)
            throw new FormatException();
        else
            this._sqMtrx = new double[i, i];
        _mtrxSize = i;
    }

    public double this[int i, int j]
    {  
        get { return _sqMtrx[i, j]; }
        set { _sqMtrx[i, j] = value; }
    }

    public static Mtrx operator +(Mtrx m1, Mtrx m2)
    {
        if (m1._mtrxSize == m2._mtrxSize)
        {
            var outVal = new Mtrx(m1._mtrxSize)

            for (int i = 1; i <= m1._mtrxSize; i++)
                for (int j = 1; j <= m1._mtrxSize; j++)
                    outVal[i,j] = m1[i, j] + m2[i, j];

            return outVal;
        }
    }
}

Upvotes: 1

Xyzk
Xyzk

Reputation: 1332

You are trying to access your object like an array, instead of accessing array inside your object. try m1._sqMatrix[i,j]

Upvotes: 2

Jon Skeet
Jon Skeet

Reputation: 1500165

Well yes, the problem is here:

return m1[i, j] == m1[i, j] + m2[i, j];

This is wrong in all kinds of ways:

  • You're trying to return a bool when the operator is meant to return a Mtrx (horrible name, by the way - embrace vowels!)

  • You're trying to use an indexer on m1 and m2, which are variables of type Mtrx. You haven't created an indexer. You either need to use m1._sqMtrx[i, j] etc, or you need to declare an indexer, such as:

    public double this[int i, int j]
{
    return _sqMtrx[i, j];
}

  • Your method doesn't return anything if the two arguments have different sizes

Fundamentally I think you should think again about the whole operator.

Upvotes: 8

Related Questions