C code of two 2 by 2 matrix multiplication using Strassen algorithm:

#include<stdio.h>

int main(){

  int a[2][2],b[2][2],c[2][2],i,j;

  int m1,m2,m3,m4,m5,m6,m7;

  printf("Enter the 4 elements of first matrix: ");

  for(i=0;i<2;i++)

      for(j=0;j<2;j++)

           scanf("%d",&a[i][j]);

  printf("Enter the 4 elements of second matrix: ");

  for(i=0;i<2;i++)

      for(j=0;j<2;j++)

           scanf("%d",&b[i][j]);

  printf("\nThe first matrix is\n");

  for(i=0;i<2;i++){

      printf("\n");

      for(j=0;j<2;j++)

           printf("%d\t",a[i][j]);

  }

  printf("\nThe second matrix is\n");

  for(i=0;i<2;i++){

      printf("\n");

      for(j=0;j<2;j++)

           printf("%d\t",b[i][j]);

  }

  m1= (a[0][0] + a[1][1])*(b[0][0]+b[1][1]);

  m2= (a[1][0]+a[1][1])*b[0][0];

  m3= a[0][0]*(b[0][1]-b[1][1]);

  m4= a[1][1]*(b[1][0]-b[0][0]);

  m5= (a[0][0]+a[0][1])*b[1][1];

  m6= (a[1][0]-a[0][0])*(b[0][0]+b[0][1]);

  m7= (a[0][1]-a[1][1])*(b[1][0]+b[1][1]);

  c[0][0]=m1+m4-m5+m7;

  c[0][1]=m3+m5;

  c[1][0]=m2+m4;

  c[1][1]=m1-m2+m3+m6;

   printf("\nAfter multiplication using \n");

   for(i=0;i<2;i++){

      printf("\n");

      for(j=0;j<2;j++)

           printf("%d\t",c[i][j]);

   }

   return 0;

}

Sample output:

Enter the 4 elements of first matrix: 1

2

3

4

Enter the 4 elements of second matrix: 5

6

7

8

The first matrix is

1       2

3       4

The second matrix is

5       6

7       8

After multiplication using

19      22

43      50