Thread: Matrices multiplication

I am unable to input the correct form for matrices multiplication. I have an exam tomorrow in which I need to use this. Please help me.

Code:

#include <stdio.h>
#include <conio.h>
int main()
{
    float a[10][10], b[10][10], c[10][10];
    int i, j, k, l, n=0, m=0, x=0, y=0, sum=0;
    printf("Enter the number of rows and collumns of the first matrix");
    scanf("%d %d", &n, &m);
    printf("What are the elements of the first matrix?\n");
    for (i = 0; i < n; i++)
    {
        for (j = 0; j < m; j++)
        {
            scanf("%f", &a[i][j]);
        }
    }
    printf("Enter the number of rows and collumns of the second matrix");
    scanf("%d %d", &k, &l);
    if (m != l)
    {
        printf("these matrices cannot be multiplied");
    }
    else
    {
        printf("What are the elements of the second matrix?\n");
        for (i = 0; i < k; i++)
        {
            for (j = 0; j < l; j++)
            {
                scanf("%f", &b[k][l]);
            }
        }
        printf("Your matrices are \n");
        for (i = 0; i < n; i++)
        {
            for (j = 0; j < m; j++)
            {
                printf("%f ", a[i][j]);
                
            }
            printf("\n");
        }
        printf("\n");
        for (i = 0; i < k; i++)
        {
            for (j = 0; j < l; j++)
            {
                printf("%f ", b[k][l]);
            }
            printf("\n");
        }
        printf("\n");
        for (i = 0; i < n; i++)
        {
            for (j = 0; j < k; j++);
            {    sum = 0;
                for (x = 0; x < l; x++)
                {
                    sum += a[i][x] * b[x][j];

                }
                c[i][j] = sum;
                sum = 0;
            }
        }
        printf("\n");
        printf("The multiplication of the matrices is");
        for (i = 0; i < n; i++)
        {
            for (j = 0; j < l; j++)
            {
                printf("%f\t", c[i][j]);
                printf("\t");
            }
            printf("\n");
        }
        printf("\n");
    }
    getch();
}

Please be a bit more specific. I'm not that keen on running a program where I have to be sitting around inputting values into matrices all night, and your variable names are pretty off putting, so I really don't want to spend time reading your code either to be honest.

I would actually advice that you have 3 precomputed matrices, one for the first matrix, one for the the second and one for the answer. Then you define a fourth one, which you use to store the result on running your algorithm on the first 2 matrices. That way you don't have to spend time on inputting values while testing and you can have the third matrix to compare your computed answer with, so you know that you did it right.

Then add the code for inputting values, when you know that the rest of the code is correct, if you really feel the need to have manual input.

Originally Posted by grumpy

Line 55 in your previous listing. Specific enough?

I think you maybe misunderstood my post, which was directed towards the OP and not Salem, or maybe you where giving the OP a nudge?

Either way, your post was very specific indeed! :-)

The more direct approach. I like it! :-)

This is what I did. It works now

Code:

#include <stdio.h>
#include <conio.h>

int main()
{
    int first[10][10], second[10][10], i, j, m, n, l, k, x, sum = 0, multiplication[10][10];
    printf("Enter the number of rows and columns of the first matrix\n");
    scanf("%d %d", &m, &n);
    printf("Enter the elements of the first matrix\n");
    for (i = 0; i < m; i++)
    for (j = 0; j < n; j++)
        scanf("%d", &first[i][j]);
    printf("Enter the number of rows and columns of the second matrix\n");
    scanf("%d %d", &l, &k);
    printf("Enter the elements of the second matrix\n");
    for (i = 0; i < l; i++)
    for (j = 0; j < k;j++)
        scanf("%d", &second[i][j]);
    printf("Your matrices are \n");
    for (i = 0; i < m; i++)
    {
        for (j = 0; j < n; j++)
            printf("%d\t", first[i][j]);
        printf("\n");
    }
    printf("\n");
    for (i = 0; i < l; i++)
    {
        for (j = 0; j < k; j++)
            printf("%d\t", second[i][j]);
        printf("\n");
    }
    for (i = 0; i < m; i++)
    {
        for (j = 0; j < k; j++)
        {
            for (x = 0; x < l; x++)
            {
                sum = sum + first[i][x]*second[x][j];
            }

            multiplication[i][j] = sum;
            sum = 0;
        }
    }
    

    printf("The multiplication of the matrices is:\n");
    for (i = 0; i < m; i++)
    {
        for (j = 0; j < k; j++)
            printf("%d \t", multiplication[i][j]);
        printf("\n");
    }
    
    
    
    



    getch();
    

}