Example: Matrix Multiplication Using Functions in C++

// Matrix Multiplication Using Functions
#include <iostream>
#include <vector> // Required for std::vector

using namespace std;

// Function to get matrix input from the user
void inputMatrix(vector<vector<int>>& matrix, int rows, int cols) {
    cout << "Enter elements for the matrix (" << rows << "x" << cols << "):" << endl;
    for (int i = 0; i < rows; ++i) {
        for (int j = 0; j < cols; ++j) {
            cout << "Enter element at [" << i << "][" << j << "]: ";
            cin >> matrix[i][j];
        }
    }
}

// Function to multiply two matrices
vector<vector<int>> multiplyMatrices(const vector<vector<int>>& matrixA, 
                                     const vector<vector<int>>& matrixB,
                                     int r1, int c1, int r2, int c2) {
    // Check if multiplication is possible
    if (c1 != r2) {
        cout << "Error: Number of columns in the first matrix must be equal to the number of rows in the second matrix." << endl;
        // Return an empty matrix to indicate error or handle differently
        return {}; 
    }

    // Initialize result matrix with dimensions r1 x c2, filled with zeros
    vector<vector<int>> resultMatrix(r1, vector<int>(c2, 0));

    // Perform matrix multiplication
    for (int i = 0; i < r1; ++i) { // Iterate over rows of matrix A
        for (int j = 0; j < c2; ++j) { // Iterate over columns of matrix B
            for (int k = 0; k < c1; ++k) { // Iterate over columns of A OR rows of B
                resultMatrix[i][j] += matrixA[i][k] * matrixB[k][j];
            }
        }
    }
    return resultMatrix;
}

// Function to display a matrix
void displayMatrix(const vector<vector<int>>& matrix) {
    if (matrix.empty() || matrix[0].empty()) {
        cout << "Matrix is empty or invalid." << endl;
        return;
    }
    cout << "Resultant Matrix:" << endl;
    for (const auto& row : matrix) {
        for (int val : row) {
            cout << val << "\t";
        }
        cout << endl;
    }
}

int main() {
    // Step 1: Declare dimensions for the two matrices
    int r1, c1, r2, c2;

    cout << "Enter dimensions for Matrix A (rows cols): ";
    cin >> r1 >> c1;
    cout << "Enter dimensions for Matrix B (rows cols): ";
    cin >> r2 >> c2;

    // Step 2: Create matrices using std::vector<std::vector<int>>
    vector<vector<int>> matrixA(r1, vector<int>(c1));
    vector<vector<int>> matrixB(r2, vector<int>(c2));

    // Step 3: Get input for Matrix A
    inputMatrix(matrixA, r1, c1);

    // Step 4: Get input for Matrix B
    inputMatrix(matrixB, r2, c2);

    // Step 5: Perform matrix multiplication using the function
    vector<vector<int>> resultMatrix = multiplyMatrices(matrixA, matrixB, r1, c1, r2, c2);

    // Step 6: Display the result matrix
    if (!resultMatrix.empty()) { // Check if multiplication was successful (not an empty error matrix)
        displayMatrix(resultMatrix);
    } else {
        cout << "Matrix multiplication could not be performed due to incompatible dimensions." << endl;
    }
    
    return 0;
}