Matrix multiplication by loops-CodePudding

This is the template and initialization of variables.

#include <stdio.h>
int main()
{
    int k=0,m=0,l=0,s=0; 
    int a[k][m],a1[m][l],c[k][l];

Inputting the matrix dimensions and entering the elements individually

//Inputting the matrices...

printf("Enter the dimension of first matrix (row and column)>> \n");
scanf("%d%d",&k,&m);
printf("Enter the dimension of second matrix (row and column)>> \n");
scanf("%d%d",&k,&m);
printf("First matrix elements are inputted from below >> \n");
for (int i = 0; i < k ; i  )
{
    for (int j = 0; j < m; j  )
    {
        printf("a[%d][%d]>> ",i,j);
        scanf("%d",&a[i][j]);
    }
    printf("\n");
}

Inputting the second matrix

printf("Second matrix elements are inputted from below >> \n");
for (int i = 0; i < m ; i  )
{
    for (int j = 0; j < l; j  )
    {
        printf("a[%d][%d]>> ",i,j);
        scanf("%d",&a[i][j]);
    }
    printf("\n");
}

Here's the logic for matrix multiplication

//Logic for the matrix multiplication

for (int i = 0; i < k; i  )
{
    for (int j = 0; j < l; j  )
    {
        s=0;
        for (int jj = 0; jj < m; jj  )
        {
            s =a[i][jj]*a1[jj][j];
        }
        c[i][j]=s;
    }
}

Printing the multiplied matrix

//for outputting the matrix
                                                
for (int i = 0; i < k ; i  )
{
    for (int j = 0; j < l; j  )
    {
        printf("a[%d][%d] = %d",k,l,c[k][l]);
        
    }
    printf("\n");
}
return 0;

Respected experienced coders please help me out in this one. I am stuck for a while now.

I inputted two matrices of order [k][m] and [m][l]. I then multiplied them by this logic.

And then I simply printed the final matrix c[k][l] by some nested loops.

Please kindly help me.

The output of the following code in an online compiler Enter the dimension of first matrix (row and column)>>

2 2

Enter the dimension of second matrix (row and column)>>

2 2

First matrix elements are inputted from below >>

a[0][0]>> 2

a0>> 2

a[1][0]>> 2

a1>> 2

Second matrix elements are inputted from below >>

onlinegdb compiler

CodePudding user response：

Hey, I have modified your code. Hope this will help you.

#include <stdio.h>
int main()
{
    int k, m, l, x;

    //Entering matrix dimensions
    printf("Enter the dimension of first matrix (row and column)>> \n");
    scanf("%d%d", &k, &m);
    printf("Enter the dimension of second matrix (row and column)>> \n");
    scanf("%d%d", &m, &l);
    printf("First matrix elements are inputted from below >> \n");

    int a[k][m];
    //Entering matrix elements
    for (int i = 0; i < k; i  )
    { 
       for (int j = 0; j < m; j  )
       {
            printf("a[%d][%d]>> ", i, j);
            scanf("%d", &a[i][j]);
        }
        printf("\n");
    }
    int a1[m][l];
    printf("Second matrix elements are inputted from below >> \n");
    for (int i = 0; i < m; i  )
    {
        for (int j = 0; j < l; j  )
        {
            printf("a1[%d][%d]>> ", i, j);
            scanf("%d", &a1[i][j]);
        }
        printf("\n");
    }

    //Matrix multiplication logic
    int c[k][l];
    for (int i = 0; i < k; i  )
    {
        for (int j = 0; j < m; j  )
        {
            c[i][j] = 0;
            for (int x = 0; x < m; x  )
            {
                c[i][j]  = a[i][x] * a1[x][j];
            }
        }
    }
    //Displaying product matrix
    for (int i = 0; i < k; i  )
    {
        for (int j = 0; j < l; j  )
        {
            printf("\t%d", c[i][j]);
        }
        printf("\n");
    }
    return 0;
}

Tips

Declare array for each matrix after the declaration of its row and column variables.
c[i][j] = a[i][x] * a1[x][j]; is one major part of the logic of matrix multiplication which you missed out.
You entered the matrix dimension variables the same for both matrices.

CodePudding user response：

There are multiple problems:

The matrix arrays must be defined after the values of their dimensions have been read. As posted, the behavior is undefined because the dimensions are 0.
the dimensions of the second matrix are input with scanf("%d%d", &k, &m); into k and m instead of m and l. The first dimension should actually be either assumed to be the same as the second dimension of the first matrix or checked.
the input loop for the second matrix stores the values into a instead of a1: a typical cut and paste bug.
The printing statement printf("a[%d][%d] = %d",k,l,c[k][l]); is incorrect: the index variables are i and j, so the statement should be:
```
  printf("a[%d][%d] = %d\n", i, j, c[i][j]);
```

Here is a modified version:

#include <stdio.h>

int main() {
    int k, m, m1, l; 

    //Inputting the matrices...
    printf("Enter the dimensions of first matrix (rows and columns)>> \n");
    if (scanf("%d%d", &k, &m) != 2)
        return 1;
    printf("Enter the dimensions of second matrix (rows and columns)>> \n");
    if (scanf("%d%d", &m1, &l) != 2)
        return 1;

    if (k <= 0 || m <= 0 || m != m1 || l <= 0) {
        printf("incompatible dimensions\n";
        return 1;
    }
    int a[k][m], a1[m][l], c[k][l];

    printf("First matrix elements are inputted from below >> \n");
    for (int i = 0; i < k; i  ) {
        for (int j = 0; j < m; j  ) {
            printf("a[%d][%d]>> ", i, j);
            if (scanf("%d", &a[i][j]) != 1)
                return 1;
        }
        printf("\n");
    }

    printf("Second matrix elements are inputted from below >> \n");
    for (int i = 0; i < m; i  ) {
        for (int j = 0; j < l; j  ) {
            printf("a1[%d][%d]>> ", i, j);
            if (scanf("%d", &a1[i][j]) != 1)
                return 1;
        }
        printf("\n");
    }

    //Logic for the matrix multiplication
    for (int i = 0; i < k; i  ) {
        for (int j = 0; j < l; j  ) {
            int s = 0;
            for (int jj = 0; jj < m; jj  ) {
                s  = a[i][jj] * a1[jj][j];
            }
            c[i][j] = s;
        }
    }

    //for outputting the matrix
    for (int i = 0; i < k; i  ) {
        for (int j = 0; j < l; j  ) {
            printf(" %d", c[i][j]);
        }
        printf("\n");
    }
    return 0;
}