Multiplication of 2 Matrix in C

JamesBond's Avatar author of Multiplication of 2 Matrix in C
This is an article on Multiplication of 2 Matrix in C in C.

Background



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



Code: C
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");
    }
}
Prasannaa, shabbir likes this
elena's Avatar, Join Date: May 2007
Newbie Member
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's Avatar, Join Date: Jan 2008
TechCake
If you are user of Visual Studio (VC8) then you can easily use this

Code:
#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.
Dhananjay Sirsat like this
wtfmate's Avatar, Join Date: Jan 2010
Newbie Member
Quote:
Originally Posted by asadullah.ansari View Post
If you are user of Visual Studio (VC8) then you can easily use this

Code:
#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.
There is a bug in this code; the inner most for loop should be:

for(k=0;k<r2;k++) { ... }
mclark's Avatar, Join Date: Mar 2010
Newbie Member
I'm using xcode as my compiler, and it's stating that there are 2 bugs...
the first bug is on the second line where the "{" is. Xcode is says, "Return type of 'main' is not 'int'"... what does this mean?

and... the other bug is on the 72 line, where the getch() statement is.. xcode says, "Implicit declaration of function 'getch'"...

any idea of how to correct these two bugs?
tajender's Avatar, Join Date: Mar 2010
Newbie Member
broncha's Avatar, Join Date: Apr 2010
Newbie Member
Quote:
Originally Posted by mclark View Post
I'm using xcode as my compiler, and it's stating that there are 2 bugs...
the first bug is on the second line where the "{" is. Xcode is says, "Return type of 'main' is not 'int'"... what does this mean?

and... the other bug is on the 72 line, where the getch() statement is.. xcode says, "Implicit declaration of function 'getch'"...

any idea of how to correct these two bugs?
For the first bug change the data type of main from void to int . and at the end before closing main function "return 0"

Code:
int main()
for the second bug :
Are you including conio.h ?for getch() you should include conio.h
3eenjohn's Avatar, Join Date: Apr 2010
Newbie Member
I have a very urgent Question ..... How to make a program which support brackets () and maths operations +-/* from user to input in a string ???
eg : [ (2+4) , 5*7 , ...... ]
Please it's urgent
and if any one knew the answer please thankfully could he send the program to my e-mail ( dodo-makram@hotmail.com )
user2390's Avatar, Join Date: Dec 2010
Newbie Member
the above codes has one logical error in multiplying 2 matrices......
the correct portion of the codes:
for(i=0;i<r1;i++)
{
for(j=0;j<c2;j++)
{
mult[i][j]=0;
for(k=0;k<r1;k++)
{
....
user2390's Avatar, Join Date: Dec 2010
Newbie Member
Excuse me ........
the correct portion is:
for(i=0;i<r1;i++)
{
for(j=0;j<c2;j++)
{
mult[i][j]=0;
for(k=0;k<c1;k++)
{
......