Multiplication of 2 Matrix in C

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Background

The output to the Matrix multiplication will be generated as follows.

a11 a12 a13   A11 A12 A13   a11xA11+a12xA21+a13xA31 a11xA12+a12xA22+a13xA32
a21 a22 a23 x A21 A22 A23 = a21xA11+a22xA21+a23xA31 a21xA12+a22xA22+a23xA32
a31 a32 a33   A31 A32 A33   a31xA11+a32xA21+a33xA31

More specific details are beyond the scope of this article but you can refer Matrix multiplication in wikipedia.

The Code

void main()
{
    int m1[10][10],i,j,k,m2[10][10],add[10][10],mult[10][10],r1,c1,r2,c2;
    printf("Enter number of rows and columns of first matrix MAX 10\n");
    scanf("%d%d",&r1,&c1);
    printf("Enter number of rows and columns of second matrix MAX 10\n");
    scanf("%d%d",&r2,&c2);
    if(r2==c1)
    {
        printf("Enter rows and columns of First matrix \n");
        printf("Row wise\n");
        for(i=0;i<r1;i++)
        {
            for(j=0;j<c1;j++)
                scanf("%d",&m1[i][j]);
        }
        printf("You have entered the first matrix as follows:\n");
        for(i=0;i<r1;i++)
        {
            for(j=0;j<c1;j++)
                printf("%d\t",m1[i][j]);
            printf("\n");
        }
        printf("Enter rows and columns of Second matrix \n");
        printf("Again row wise\n");
        for(i=0;i<r2;i++)
        {
            for(j=0;j<c2;j++)
                scanf("%d",&m2[i][j]);
        }
        printf("You have entered the second matrix as follows:\n");
        for(i=0;i<r2;i++)
        {
            for(j=0;j<c2;j++)
                printf("%d\t",m2[i][j]);
            printf("\n");
        }
        if(r1==r2&&c1==c2)
        {
            printf("Now we add both the above matrix \n");
            printf("The result of the addition is as follows;\n");
            for(i=0;i<r1;i++)
            {
                for(j=0;j<c1;j++)
                {
                    add[i][j]=m1[i][j]+m2[i][j];
                    printf("%d\t",add[i][j]);
                }
                printf("\n");
            }
        }
        else
        {
            printf("Addition cannot be done as rows or columns are not equal\n");
        }
        printf("Now we multiply both the above matrix \n");
        printf("The result of the multiplication is as follows:\n");
        /*a11xA11+a12xA21+a13xA31 a11xA12+a12xA22+a13xA32 a11xA13+a12xA23+a13xA33*/
        for(i=0;i<r1;i++)
        {
            for(j=0;j<c2;j++)
            {
                mult[i][j]=0;
                for(k=0;k<r1;k++)
                {
                    mult[i][j]+=m1[i][k]*m2[k][j];
                    /*mult[0][0]=m1[0][0]*m2[0][0]+m1[0][1]*m2[1][0]+m1[0][2]*m2[2][0];*/
                }
                printf("%d\t",mult[i][j]);
            }
            printf("\n");
        }
        getch();
    }
    else
    {
        printf("Matrix multiplication cannot be done");
    }
}

[elena]

I'm a student and I've got to realize matrix multiplication using threads. I know how to do it without threads, but with threads it seems to me a little confusing, cause I haven't used threads.

[asadullah.ansari]

If you are user of Visual Studio (VC8) then you can easily use this

#include<omp.h>

omp_set_num_threads(2 or 4 or 6) // as depends on your loop
#pragma omp parallel for shared(mult, r1,c2) private(j,k) 
 for(i=0;i<r1;i++)
        {
            for(j=0;j<c2;j++)
            {
                mult[i][j]=0;
                for(k=0;k<r1;k++)
                {
                    mult[i][j]+=m1[i][k]*m2[k][j];
                    /*mult[0][0]=m1[0][0]*m2[0][0]+m1[0][1]*m2[1][0]+m1[0][2]*m2[2][0];*/
                }
               //printf("%d\t",mult[i][j]);
            }
            //printf("\n");
        }

By the use of OpenMP, parallel computing will be done. Today Google is using OpenMP, MPI, Grid Computing.