C++ program to implement the use of Dynamic Constructor (Matrix Addition):

DynamicConstructor.cpp

    #include<iostream>

    using namespace std;

    class matrix{
        int **a;
        int m,n;

        public:
            matrix(int x,int y);
            ~matrix();
            void initialize();
            void add(matrix p,matrix q);
            void display();
    };

    matrix:: matrix(int x,int y){
        m=x;
        n=y;
        a=new int*[x];
        int i,j;
        for(i=0;i<x;i++){
            a[i]=new int[y];
        }
        for(i=0;i<x;i++){
            for(j=0;j<y;j++){
                a[i][j]=0;
            }
        }
    }

    matrix:: ~matrix(){
        int i;
        for(i=0;i<m;i++){
            delete a[i];
        }
    }

    void matrix:: initialize(){
        cout<<"\nEnter the elements of the matrix..\n";
        int i,j;
        for(i=0;i<m;i++){
            for(j=0;j<n;j++){
                cin>>a[i][j];
            }
        }
    }

    void matrix:: add(matrix p,matrix q){
        int i,j;
        for(i=0;i<m;i++){
            for(j=0;j<n;j++){
                    a[i][j]=p.a[i][j]+q.a[i][j];
            }
        }
    }

    void matrix:: display(){
        int i,j;
        for(i=0;i<m;i++){
            for(j=0;j<n;j++){
                cout<<a[i][j]<<" ";
            }
            cout<<endl;
        }
    }

    int main(){
        int p,q,x,y;
        cout<<"Enter the no of rows and columns of first matrix..";
        cin>>x>>y;
        matrix a(x,y);
        a.initialize();
        cout<<"\nEnter the no of rows and columns of second matrix..";
        cin>>p>>q;
        matrix b(p,q);
        b.initialize();
        matrix c(x,y);
        c.add(a,b);
        cout<<"\nThe Addition of the matrices is..\n";
        c.display();
        return 0;
    }