Question

I am trying to write 2 functions, one to read the matrix (2D array) and other one to print it out. So far I have:

    /* Read a matrix: allocate space, read elements, return pointer. The
       number of rows and columns are given by the two arguments. */
    double **read_matrix(int rows, int cols){

        double **mat = (double **) malloc(sizeof(double *)*rows);
        int i=0;
        for(i=0; i<rows; i++){
        /* Allocate array, store pointer  */
        mat[i] = (double *) malloc(sizeof(double)*cols); 
       //what to do after??

         return mat;
    }

then the print matrix function, not sure if it is correct

void print_matrix(int rows, int cols, double **mat){
    for(i=0; i<rows; i++){    /* Iterate of each row */
      for(j=0; j<cols; j++){  /* In each row, go over each col element  */
      printf("%f ",mat[i][j]); /* Print each row element */
  }
}
}

and here is the main function I am using to run:

    #include <stdlib.h>


    double **read_matrix(int rows, int cols);
    void print_matrix(int rows, int cols, double **mat);
    void free_matrix(int rows, double **mat);

    int main(){

      double **matrix;
      int rows, cols;
      /* First matrix */
      printf("Matrix 1\n");
      printf("Enter # of rows and cols: ");
      scanf("%d %d",&rows,&cols);
      printf("Matrix, enter %d reals: ",rows*cols);
      matrix = read_matrix(rows,cols); 
      printf("Your Matrix\n");  /* Print the entered data */
      print_matrix(rows,cols,matrix);
      free_matrix(rows, matrix);   /* Free the matrix */

        return 0;
}

Answer 1

Try this one. may be helpful to you.

#include <stdio.h>
#include <stdlib.h>

double **read_matrix(int rows, int cols);
void print_matrix(int rows, int cols, double **mat);
void free_matrix(int rows, double **mat);

double **read_matrix(int rows, int cols){

    double **mat = (double **) malloc(sizeof(double *)*rows);
    int i=0,j=0;
    for(i=0; i<rows; i++)
    /* Allocate array, store pointer  */
        mat[i] = (double *) malloc(sizeof(double)*cols); 

       for(i=0; i<rows; i++){
           for(j=0; j<cols; j++){
               scanf("%lf",&mat[i][j]);
           }
       }
     return mat;
}

void print_matrix(int rows, int cols, double **mat){
    int i=0,j=0;
  for(i=0; i<rows; i++){    /* Iterate of each row */
        for(j=0; j<cols; j++){  /* In each row, go over each col element  */
            printf("%lf ",mat[i][j]); /* Print each row element */
        }
        printf("\n");
    }
}

void free_matrix(int rows, double **mat){
    int i=0;
    for(i=0;i<rows;i++)    
        free(mat[i]);
    free(mat);
}

int main(){

  double **matrix;
  int rows, cols;
  /* First matrix */
  printf("Matrix 1\n");
  printf("Enter # of rows and cols: ");
  scanf("%d%d",&rows,&cols);
  printf("Matrix, enter %d reals: \n",rows*cols);
  matrix = read_matrix(rows,cols); 
  printf("Your Matrix\n");  /* Print the entered data */
  print_matrix(rows,cols,matrix);
  free_matrix(rows, matrix);   /* Free the matrix */

  return 0;
 }

Execution:

:~$ gcc  exam.c
:~$ ./a.out 
Matrix 1
Enter # of rows and cols: 3
4
Matrix, enter 12 reals: 
1
2
3
4
5
6
7
8
9
9
0
1
Your Matrix
1.000000 2.000000 3.000000 4.000000 
5.000000 6.000000 7.000000 8.000000 
9.000000 9.000000 0.000000 1.000000