matrix in cpp code example

Example 1: matrix multipliction in c++

#include <iostream>
using namespace std;

int main()
{
    int a[10][10], b[10][10], mult[10][10], r1, c1, r2, c2, i, j, k;

    cout << "Enter rows and columns for first matrix: ";
    cin >> r1 >> c1;
    cout << "Enter rows and columns for second matrix: ";
    cin >> r2 >> c2;

    // If column of first matrix in not equal to row of second matrix,
    // ask the user to enter the size of matrix again.
    while (c1!=r2)
    {
        cout << "Error! column of first matrix not equal to row of second.";

        cout << "Enter rows and columns for first matrix: ";
        cin >> r1 >> c1;

        cout << "Enter rows and columns for second matrix: ";
        cin >> r2 >> c2;
    }

    // Storing elements of first matrix.
    cout << endl << "Enter elements of matrix 1:" << endl;
    for(i = 0; i < r1; ++i)
        for(j = 0; j < c1; ++j)
        {
            cout << "Enter element a" << i + 1 << j + 1 << " : ";
            cin >> a[i][j];
        }

    // Storing elements of second matrix.
    cout << endl << "Enter elements of matrix 2:" << endl;
    for(i = 0; i < r2; ++i)
        for(j = 0; j < c2; ++j)
        {
            cout << "Enter element b" << i + 1 << j + 1 << " : ";
            cin >> b[i][j];
        }

    // Initializing elements of matrix mult to 0.
    for(i = 0; i < r1; ++i)
        for(j = 0; j < c2; ++j)
        {
            mult[i][j]=0;
        }

    // Multiplying matrix a and b and storing in array mult.
    for(i = 0; i < r1; ++i)
        for(j = 0; j < c2; ++j)
            for(k = 0; k < c1; ++k)
            {
                mult[i][j] += a[i][k] * b[k][j];
            }

    // Displaying the multiplication of two matrix.
    cout << endl << "Output Matrix: " << endl;
    for(i = 0; i < r1; ++i)
    for(j = 0; j < c2; ++j)
    {
        cout << " " << mult[i][j];
        if(j == c2-1)
            cout << endl;
    }

    return 0;
}

Example 2: matrix class in c++

template<class T>
class matrix{
    size_t ROW,COL;
    vector<vector<T>> mat;
public:
    matrix(size_t N, size_t M, int populate = 0){
        this->ROW = N;
        this->COL = M;
        this->mat = vector<vector<T>> (ROW,vector<T> (COL,populate));
    }
    matrix(size_t N, int populate = 0){
        this->ROW = N;
        this->COL = N;
        this->mat = vector<vector<T>> (ROW,vector<T> (COL,populate));
    }
    void __init(){
        for(int i = 0; i < ROW; ++i){
            for(int j = 0; j < COL; ++j){
                cin  >> this->mat[i][j];
            }
        }
    }
    void __display(){
        for(int i = 0; i < ROW; ++i){
            for(int j = 0; j < COL; ++j){
                cout << this->mat[i][j] << " ";
            }
            cout << "\n";
        }
    }
    matrix<T> operator*(const matrix &rhs)const{
        if(this->COL != rhs.ROW){
            throw "MATRIX MULTIPLICATION CANNOT HAPPEN WITH THE GIVEN MATRICES"
        }
        matrix<T> result(this->ROW,rhs.COL);
        for(int _i = 0; _i < this->ROW; _i++){
            for(int _j = 0; _j < rhs.COL; _j++){
                result[_i][_j] = 0;
                for(int _k = 0; _k < this->COL; ++_k){
                    result[_i][_j]+=(this->mat[_i][_k]*rhs.mat[_k][_j]);
                }
            }
        }
        return result;
    }
    matrix<T> power(int n){
        if(n == 0)return matrix<T>(this->ROW, this->COL,1);
        if(n == 1)return *this;
        matrix p = power(n/2);
        p = p*p;
        if(n%2)p = p*(*this);
        return p;
    }
};

Example 3: create matrix cpp

typedef std::vector<std::vector<double> > Matrix;
//with initialization
Matrix matrix1 = { {0.1,1.1,.2},
                 {.4,.5,.6}, 
                 {.8,.9,.10}
                };
//just initiation (3x3)
Matrix matrix2(3, std::vector<double>(3) );