Create a 2D array using the / malloc pointer, and then print it

Question

I am trying to write 2 functions, one for reading a matrix (2D array) and another for printing it. So far, I:

/* 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 that I use to run:

 #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); 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 it. may be useful 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