#ifndef MATRIX_CLASS#define MATRIX_CLASS#include <iostream>#include <vector>#include "d_except.h"using namespace std;template <typename T>class matrix{	public:		matrix(int numRows = 1, int numCols = 1, const T& initVal = T());			// constructor.			// Postcondition: create array having numRows x numCols elements			// all of whose elements have value initVal		vector<T>& operator[] (int i);			// index operator.			// Precondition: 0 <= i < nRows. a violation of this			// precondition throws the indexRangeError exception.			// Postcondition: if the operator is used on the left-hand			// side of an assignment statement, an element of row i 			// is changed		const vector<T>& operator[](int i) const;			// version for constant objects      int rows() const;			// return number of rows      int cols() const;			// return number of columns      void resize(int numRows, int numCols);			// modify the matrix size.			// Postcondition: the matrix has size numRows x numCols.			// any new elements are filled with the default value of type T	private:      int nRows, nCols;			// number of rows and columns      vector<vector<T> > mat;			// matrix is implemented as nRows vectors (rows),			// each having nCols elements (columns)};template <typename T>matrix<T>::matrix(int numRows, int numCols, const T& initVal):	nRows(numRows), nCols(numCols),	mat(numRows, vector<T>(numCols,initVal)){}// non-constant version. provides general access to matrix// elementstemplate <typename T>vector<T>& matrix<T>::operator[] (int i){	if (i < 0 || i >= nRows)		throw indexRangeError(		 	"matrix: invalid row index", i, nRows);   return mat[i];}// constant version.  can be used with a constant object.// does not allow modification of a matrix elementtemplate <typename T>const vector<T>& matrix<T>::operator[] (int i) const{	if (i < 0 || i >= nRows)		throw indexRangeError(			"matrix: invalid row index", i, nRows);   return mat[i];}template <typename T>int matrix<T>::rows() const{   return nRows;}template <typename T>int matrix<T>::cols() const{   return nCols;}template <typename T>void matrix<T>::resize(int numRows, int numCols){   int i;      // handle case of no size change with a return   if (numRows == nRows && numCols == nCols)      return;	// assign the new matrix size	nRows = numRows;	nCols = numCols;	// resize to nRows rows	mat.resize(nRows);	// resize each row to have nCols columns	for (i=0; i < nRows; i++)		mat[i].resize(nCols);}#endif	// MATRIX_CLASS