A template for matrix expressions

Matrix_Template.cpp

#include<iostream>
#include<vector>
#include<utility>	// for std:: pair
#include<stdbool.h>	// for bool datatype
#include<iomanip>	// for formatted printing ( padding ) in show()
using namespace std;

template<typename T>
class matrix{
	private:	
		vector< vector<T> > v;	//vector of vectors, just like a 2D array
		int ROW,COL;
		T det();		// for calculating determinant 
	public:
		matrix(int row=0,int col=0,T val=(T)0);	// constructor, can be used at default constructor due to default parameters
		pair<int,int> row_col();	//  returns a pair containg number of rows and columns
		matrix<T>& show();		// prints whole matrix
		T get_val(int row,int col);
		matrix<T>& set_all(T val,bool diag=false);	// depending on flag value, assigns all(or diagonal elements) the provided value
		matrix<T>& set_val(int row,int col,T val);
		matrix<T>& operator+(matrix<T>& mat);
		matrix<T>& operator-(matrix<T>& mat);

};

template<typename T>
matrix<T>::matrix(int row,int col,T val)
	:ROW(row),		// member list initialisation........
	COL(col){		
	v.resize(row,vector<T> (col));
	set_all(val);	// can be skipped and directly initialised in v.resize 
}

template<typename T>
pair<int,int> matrix<T>::row_col(){
	return {ROW,COL};
}

template<typename T>
matrix<T>& matrix<T>::show(){
	for(auto i:v){
		for(auto j:i)
			cout<<setw(4)<<j<<" ";		// padding
		cout<<endl;
	}
	return *this;	// function chaining
}

template<typename T>
T matrix<T>::get_val(int row,int col){
	if(row<ROW && col<COL)
		return v[row][col];
	else cout<<"That doesn't exist. Check row and col !. Giving a random value.\n";
		return v[0][0];
}

template<typename T>
matrix<T>& matrix<T>::set_all(T val,bool diag){		// if diag is true, it assigns diagonal elements only.
	int ROW=row_col().first ,COL=row_col().second ;
	for(int i=0;i<ROW;i++){
		for(int j=0;j<COL;j++){
			if(i!=j && diag==true)	// add && ROW==COL if you want strictly diagonal elements to be assigned (in case of square matrix)
				continue;
			set_val(i,j,val);				//v[i][j]=val;
		}
	}

	return *this;
}

template<typename T>
matrix<T>& matrix<T>::set_val(int row,int col,T val){
	if(row<ROW && col<COL)
		v[row][col]=val;
	else cout<<"That doesn't exist. Check size !\n";
	return *this;
}


template<typename T>
matrix<T>& matrix<T>::operator+(matrix<T>& mat){
	if(make_pair(ROW,COL)!=mat.row_col()){
		cout<<"Can't add"<<endl;		// you may change this to throw some error
		return *this;
	}
	for(int i=0;i<ROW;i++){
		for(int j=0;j<COL;j++)
			v[i][j]+=mat.get_val(i,j);
	}


	return *this;
}

template<typename T>
matrix<T>& matrix<T>::operator-(matrix<T>& mat){
	if(make_pair(ROW,COL)!=mat.row_col()){
		cout<<"Can't subtract"<<endl;		// you may change this to throw some error
		return *this;
	}
	for(int i=0;i<ROW;i++){
		for(int j=0;j<COL;j++)
			v[i][j]-=mat.get_val(i,j);
	}

	return *this;
}


int main(){
	matrix<int> mymatrix(2,3),my(2,3),var(2,3);
	// my.set_val(1,1,5);
	(mymatrix-my.set_all(1,true)+var.set_all(5)).show();
	//mymatrix.set_val(1,0,45).show();

	return 0;
}