C++ Program to multiply two Matrices

One can define matrices in C++ using 2-D arrays.

In this post I will assume, that you are familiar with the concepts of arrays.

In this post I will show you how to write a C++ program that gives the product of two matrices.

The product of two matrices isn’t always defined.
The product of matrices $A$ and $B$ :
$A\times B$ is defined only when the no. of columns of $A$ is equal to the no. of rows in matrix $B$ .

If $A$ is an $m\times p$ matrix, and $B$ is an $p\times n$ matrix, then the product matrix would be a $m\times n$ matrix,
$(A\times B)_{ij} = \sum_{k=1}^pA_{ik}B_{kj}$

With the above, information, we can proceed to write a simple program, to multiply two matrices of given sizes.
We would also need to check whether the matrix product is defined or not.

The program is pretty much self-explanatory.

PROGRAM:

//Matrix Multiply
#include<iostream>
#include<iomanip>
using namespace std;
int main()
{
	int m,n,p,q;
	
	a:cout<<"\nEnter the order of the matrix A:\n";
	cin>>m;
	cin>>n;
	cout<<"\nEnter the order of the matrix B:\n";
	cin>>q;
	cin>>p;
	if(n!=q){
		cout<<"\nCan't multiply!\nThe number of columns of A should be equal to the number of rows in B.\n\nPlease enter again!\n\n";
		goto a;
	}
	double a[m][n];
	double b[n][p];
	double prod[m][p];
	cout<<"\nEnter the elements of the matrix A row-wise:\n";
    for (int i=0;i<m;i++)
        for (int j=0;j<n;j++)    
            cin>>a[i][j];  
            
    cout<<"\nEnter the elements of the matrix B row-wise:\n";
    for (int i=0;i<n;i++)
        for (int j=0;j<p;j++)    
            cin>>b[i][j];  
	
	
	for (int i=0;i<m;i++){
		for (int j=0;j<p;j++){
			prod[i][j]=0;
			for(int k=0;k<n;k++){
				prod[i][j]=prod[i][j]+a[i][k]*b[k][j];
			}
		}
	}
	cout<<"\nThe product AxB is:\n";
	for (int i=0;i<m;i++){
        for (int j=0;j<p;j++){
        	cout<<prod[i][j]<<setw(16);
		}
        cout<<"\n";
    }   
    return 0;
}

OUTPUT:

Get Article as PDF

Manas Sharma

I’m a physicist specializing in computational material science with a PhD in Physics from Friedrich-Schiller University Jena, Germany. I write efficient codes for simulating light-matter interactions at atomic scales. I like to develop Physics, DFT, and Machine Learning related apps and software from time to time. Can code in most of the popular languages. I like to share my knowledge in Physics and applications using this Blog and a YouTube channel.

manas.bragitoff.com/