Question

Computer Science: Data Structures and Algorithms

Practice:

Construct a C++ program that takes two SQUARE matrices, and multiplies them and produces a new matrix:

Example:

[Matrix A] * [Matrix B] = [Matrix C]

(A 3x3 is the most preferred example to use)

(The first two matrices, A and B can be fixed numbers, hard-coded into the program. as opposed to user input)

Display Matrix C, also (cout etc.)

Answer 1

#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;
}

Output

Enter rows and column for first matrix: 3
2
Enter rows and column for second matrix: 3
2
Error! column of first matrix not equal to row of second.

Enter rows and column for first matrix: 2
3
Enter rows and column for second matrix: 3
2

Enter elements of matrix 1:
Enter elements a11: 3
Enter elements a12: -2
Enter elements a13: 5
Enter elements a21: 3
Enter elements a22: 0
Enter elements a23: 4

Enter elements of matrix 2:
Enter elements b11: 2
Enter elements b12: 3
Enter elements b21: -9
Enter elements b22: 0
Enter elements b31: 0
Enter elements b32: 4

Output Matrix:
24 29
6 25