# 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, int arr2, int, int, int);
int display(int result, int, int);
int main()
{
int arr1, arr2, 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, int arr2, int r, int c, int c1)
{
int i, j, k, result;

// 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, 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````