Matrix multiplication

Question

I never understand the code of matrix multiplication. Can anyone help me out?

Answer 1

The main concept is that matrix multiplication works only when number of columns of first matrix is equal to the number of rows of the second matrix. I have also included the comments in the below code. Hope you understand. If you have any doubts please reply me back. I will more than happy to solve.

#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;
}