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Multiplication of two matrices in C

Written by

Pooja Rao

Program to multiply two matrices in C

  • Product of matrices can be done when the matrices are compatible with each other.
  • The matrices are said to be compatible with each other when the number of columns of first matrix is equal to number of rows of second matrix.
  • Thus, if the first matrix has n columns and second matrix has q rows ; then n = q is essential.
  • Thus,  the elements can be multiplied using the following formula: Ci,j = Sum of ( Ai,j * Bi,k) ; where k = 1 to k < n.

Approach:

  • First we will take the number of rows and columns of each matrix as our input.
  • Next we validate if multiplication is possible, based upon number of the condition n = q; where n is number of column of first matrix and q is number of rows of second matrix.
  • Next, using the above mentioned formula we calculate the product of the matrices.
  • Here we are passing arrays between function as an input to next function.

Code:

#include <stdio.h>

void multiply(int arr1[5][5], int arr2[5][5], int, int, int);


int display(int result[5][5], int, int);


int main()


{


   int arr1[5][5], arr2[5][5], r1, c1, r2, c2, i, j;


   printf("Enter rows and column for first matrix: ");


   scanf("%d %d", &r1, &c1);


   printf("Enter rows and column for second matrix: ");


   scanf("%d %d",&r2, &c2);


   // Column of first matrix should be equal to row of second matrix


   while (c1 != r2)


   {


       printf("Error! Column of first matrix is not equal to row of second matrix.\n\n");


       printf("Enter rows and column for first matrix: ");


       scanf("%d %d", &r1, &c1);


       printf("Enter rows and column for second matrix: ");


       scanf("%d %d",&r2, &c2);


   }


   // Storing elements of first matrix.


   printf("\nEnter elements of first matrix row wise:\n");


   for(i=0; i<r1; i++)


       for(j=0; j<c1; j++)


       {


           scanf("%d", &arr1[i][j]);


       }


   // Storing elements of second matrix.


   printf("\nEnter elements of second matrix row wise:\n");


   for(i=0; i<r2; i++)


       for(j=0; j<c2; j++)


       {


           scanf("%d",&arr2[i][j]);


       }


   multiply(arr1, arr2, r1, c2, c1);


       


   return 0;


}


void multiply(int arr1[5][5], int arr2[5][5], int r, int c, int c1)


{


   int i, j, k, result[5][5];


   


   // Initializing all the elements of result matrix to 0


   for(i=0; i<r; ++i)


       for(j=0; j<c; ++j)


       {


           result[i][j] = 0;


       }


   // Multiplying matrices arr1 and arr2


   for(i=0; i<r; i++)


       for(j=0; j<c; j++)


           for(k=0; k<c1; k++)


           {


               result[i][j]+=arr1[i][k]*arr2[k][j];


           }


    


  display(result, r, c);


}


int display(int result[5][5], int r, int c)


{


   int i,j;


   


   printf("\nResult of Matrix Multiplication is:\n");


   for(i=0; i<r; i++)


   {


       for(j=0; j<c; j++)


       {


           printf("%d\t", result[i][j]);


       }


       


       printf("\n");


    }


    return 0;


}

Output:

Enter rows and column for first matrix: 1

5


Enter rows and column for second matrix: 2


3


Error! Column of first matrix is not equal to row of second matrix.


Enter rows and column for first matrix: 1


2


Enter rows and column for second matrix: 2


3


Enter elements of first matrix row wise:


1


2


Enter elements of second matrix row wise:


0


1


3


2


1


4


Result of Matrix Multiplication is:


4 3 11

Multiplication of two matrices in C