Question

Here's the main function of a C program that

• Reads in two matrices by prompting the user for their dimensions, dynamically allocating memory from the heap, and reading the values into the memory using row major ordering for the matrix values.
• Multiplies the two matrices together and puts the result into another dynamically allocated piece of memory (after checking that the dimensions are appropriate for matric multiplication).
• Outputs the two input and the result matrices.

Write the implementations of the functions input_matrix, matrix_multiply, and output_matrix (6.0%).

/*---------------------------------------------------------------------------*/
int main(void) {

    double *m1,*m2,*m3;
    int m1_rows,m1_columns,m2_rows,m2_columns;

    if (((m1 = input_matrix(&m1_rows,&m1_columns,"Matrix 1")) != NULL) &&
((m2 = input_matrix(&m2_rows,&m2_columns,"Matrix 2")) != NULL) &&
((m3 = malloc(m1_rows*m2_columns*sizeof(double))) != NULL)) {
        printf("Matrix 1\n");
        output_matrix(m1,m1_rows,m1_columns);
        printf("Matrix 2\n");
        output_matrix(m2,m2_rows,m2_columns);
        if (matrix_multiply(m1,m1_rows,m1_columns,m2,m2_rows,m2_columns,m3)) {
            printf("Product\n");
            output_matrix(m3,m1_rows,m2_columns);
            free(m1);
            free(m2);
            free(m3);
            return(0);
        } else {
            printf("Error in dimensions\n");
            free(m1);
            free(m2);
            free(m3);
            return(-1);
        }
    } else {
        free(m1);
        free(m2);
        free(m3);
        printf("Error allocating memory\n");
        return(-2);
    }
}

Answer 1

If you have any doubts, please give me comment...

#include <stdio.h>

#include <stdlib.h>

double *input_matrix(int *r, int *c, char *name);

int matrix_multiply(double *m1, int m1_rows, int m1_columns, double *m2, int m2_rows, int m2_columns, double *m3);

void output_matrix(double *m, int rows, int columns);

int main(void)

{

double *m1, *m2, *m3;

int m1_rows, m1_columns, m2_rows, m2_columns;

if (((m1 = input_matrix(&m1_rows, &m1_columns, "Matrix 1")) != NULL) &&

((m2 = input_matrix(&m2_rows, &m2_columns, "Matrix 2")) != NULL) &&

((m3 = malloc(m1_rows * m2_columns * sizeof(double))) != NULL))

{

printf("Matrix 1\n");

output_matrix(m1, m1_rows, m1_columns);

printf("Matrix 2\n");

output_matrix(m2, m2_rows, m2_columns);

if (matrix_multiply(m1, m1_rows, m1_columns, m2, m2_rows, m2_columns, m3))

{

printf("Product\n");

output_matrix(m3, m1_rows, m2_columns);

free(m1);

free(m2);

free(m3);

return (0);

}

else

{

printf("Error in dimensions\n");

free(m1);

free(m2);

free(m3);

return (-1);

}

}

else

{

free(m1);

free(m2);

free(m3);

printf("Error allocating memory\n");

return (-2);

}

}

double *input_matrix(int *r, int *c, char *name)

{

printf("Enter %s rows and columns: ", name);

scanf("%d %d", r, c);

double *m = (double *)malloc((*r) * (*c) * sizeof(double));

int i, j;

printf("Enter %s elements: ", name);

for (i = 0; i < *r; i++)

{

for (j = 0; j < *c; j++)

{

scanf("%lf", &m[i * (*c) + j]);

}

}

return m;

}

int matrix_multiply(double *m1, int m1_rows, int m1_columns, double *m2, int m2_rows, int m2_columns, double *m3)

{

if(m1_columns!=m2_rows)

return 0;

int i, j, k;

for (i = 0; i < m1_rows; i++)

{

for (j = 0; j < m2_columns; j++)

{

double sum = 0;

for (k = 0; k < m2_rows; k++)

{

sum = sum + m1[i * m1_columns + k] * m2[k * m2_columns + j];

}

m3[i * m2_columns + j] = sum;

}

}

}

void output_matrix(double *m, int rows, int columns)

{

int i, j;

for (i = 0; i < rows; i++)

{

for (j = 0; j < columns; j++)

{

printf("%.2lf ", m[i * columns + j]);

}

printf("\n");

}

}