i write code but dont understand the error please help me

#include <iostream.h>
#include <stdlib.h>
#include <conio.h>
#include <string.h>
class Matrix
{
private :
int numRows, numCols ;
int elements [30] [30] ;

public :
Matrix(){
cout<<"paratmerized constructor called";
}
Matrix( int rows , int cols ) ;
void getMatrix ( ) ;
void displayMatrix ( ) ;
Matrix :: Matrix operator+();

};
Matrix :: Matrix ( int rows = 0 , int cols = 0)
{
numCols = cols ;
numRows = rows ;
for ( int i = 0 ; i < numRows ; i ++ )
{
for ( int j = 0 ; j < numCols ; j ++ )
{
elements [ i ] [ j ] = 0 ;
}
}
}
void Matrix :: getMatrix ( )
{
for ( int i = 0 ; i < numRows ; i ++ )
{
for ( int j = 0 ; j < numCols ; j ++ )
{
cin >> elements [ i ] [ j ] ;
//cout<<"Enter the 1st Matrix";
}

}
//cout<<"Enter the 2nd Matrix"<<endl;
}
void Matrix :: displayMatrix ( )
{
for ( int i = 0 ; i < numRows ; i ++ )

{
cout << "| " ;
for ( int j = 0 ; j < numCols ; j ++ )
{
cout << elements [ i ] [ j ] << " " ;
}
cout << "|" << endl ;
}

cout<<'\n';
cout<<'\n';
}

Matrix :: Matrix operator + (Matrix add)
{
Matrix temp;
temp.numCols=numCols + add.numCols;
temp.numRows=numRows + add.numRows;
return temp;

}

void main ( )
{
Matrix matrix1(2, 2),matrix2(2,2) ;
matrix1.getMatrix ( ) ;
matrix2.getMatrix();
//Matrix = matrix1 + matrix2 ;
matrix1.displayMatrix ( ) ;
matrix2.displayMatrix ( ) ;
//

system ( "PAUSE" ) ;
getch();
}