Write a C program to convert 1D array to 2D array using pointers

Question

Write a C program to convert 1D array to 2D array using pointers. Follow the given steps to implement the above code.

1. Ask the user to input the number of rows (​ m ​ ) and the number of columns (​ n ​ ) of the 2D array. So the total number of elements of 1D array = (​ m * n ​ ) elements.

2. Call the function​ ​ input_array​ to store elements in 1D array.

   void input_array (int *arr,int size) // size = ​ m * n

3. Call the function ​ print_array​ to print the elements of 1D array.

   void print_array (int *arr, int size)

4. Call the function ​ array_to_matrix​ to convert 1D array to 2D array.

   void array_to_matrix(int **matrix, int *arr, int row, int col)

5. Call function ​ print_matrix​ to print the elements of the 2D array.

   void print_matrix(int **mat, int row, int col)

All functions should be called from the main(). Accessing and storing of elements in pointers should be carried out by using pointers only.

Code:

#include <stdio.h>
#include <stdlib.h>
#define max 100

void input_array (int *arr,int size);
void print_array (int *arr, int size);
void array_to_matrix(int **matrix, int *arr, int row, int col);
void print_matrix(int **matrix, int row, int col);


int main()
{
    int m, n, arr[max], mat[max][max];
    printf("Enter the number of rows(m):");
    scanf("%d",&m);
    printf("Enter the number of columns(n):");
    scanf("%d",&n);
    int size = m*n;

    input_array (arr,size);
    print_array (arr,size);
    array_to_matrix(mat, arr, m, n);
    print_matrix(mat, m, n);
}

void input_array (int *arr,int size)
{
    int i;
    for(i=0;i<size;i++)
    {
        printf("Enter element a[%d]",i);
        scanf("%d",&arr[i]);    
    }
}

void print_array (int *arr, int size)
{
    int i;
    printf("\n 1D array is as follows : \n");
    for(i=0;i<size;i++)
    {
        printf("%d",arr[i]);
    }
}

void array_to_matrix(int **matrix, int *arr, int row, int col)
{
    int i,j,k=0;     
    for(i=0;i<row;i++)
    {
        for(j=0;j<col;j++)
        {
            matrix[i][j] = arr[k];
            k++;
        }
    }

}

void print_matrix(int **matrix, int row, int col)
{
    int i,j;
    printf("\n 2D matrix is as follows : \n");
    for(i=0;i<row;i++)
    {
        for(j=0;j<col;j++)
        {
            printf("%d ",matrix[i][j]);
        }
        printf("\n");
    }
}

Error: I am getting a segmentation fault. The problem I am having is related to pointer to the arrays and how to pass them to the function.

Answer 1

in

void main()
{
    int m, n, arr[max], mat[max][max];
    int size = m*n;

you compute size while m and n are not yet (possibly) initialized, so the value of size is undefined with undefined behavior

In

 void array_to_matrix(int **matrix, int *arr, int row, int col)
 {
     int i,j,k=0;     
     for(i=0;i<row;i++)
     {
         for(j=0;j<col;j++)
         {
             matrix[i][j] = arr[k];
         }
     }
 }

the signature of the function says matrix is an array of pointers to int, but this is not compatible with your main where you use a 2D array. To be compatible :

void array_to_matrix(int (*matrix)[max], int *arr, int row, int col)

and same for print_matrix :

void print_matrix(int (*matrix)[max], int row, int col)

or if you prefer :

void array_to_matrix(int matrix[][max], int *arr, int row, int col)
void print_matrix(int matrix[][max], int row, int col)

But :

Write a C program to convert 1D array to 2D array using pointers

"2D array using pointers" is an is an abuse of language and means a 1D array of pointer to int, there is no 2D array.

In your previous version you limited the dimensions to 100, you do not have a reason to do that, just allocate the arrays in the heap.

Note also k always values 0 in array_to_matrix, so you always use arr[0]

And :

void main()

is wrong, main returns an int

I also encourage you to always check the result of scanf to be sure a valid input was used, else you works with non initialized value with an undefined behavior. When you read the number of rows and columns check there are not less than 1

In print_array to separate the print value with a space will help to make the result readable

Finaly :

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

void input_array (int *arr,int size);
void print_array (int *arr, int size);
void array_to_matrix(int ** matrix, int *arr, int row, int col);
void print_matrix(int ** matrix, int row, int col);


int main()
{
    int m, n, * arr, ** mat;
    int size, i;

    printf("Enter the number of rows(m):");
    if ((scanf("%d",&m) != 1) || (m < 1)) {
      puts("invalid value for rows");
      return -1;
    }

    printf("Enter the number of columns(n):");
    if ((scanf("%d",&n) != 1) || (n < 1)) {
      puts("invalid value for columns");
      return -1;
    }

    size = m*n;
    if (((arr = malloc(size * sizeof(int))) == NULL) ||
        ((mat = malloc(m * sizeof(int))) == NULL)) {
      puts("not enouh memory");
      exit(-1);
    }

    for (i = 0; i < m; ++i) {
      if ((mat[i] = malloc(n * sizeof(int))) == NULL) {
        puts("not enouh memory");
        exit(-1);
      }
    }
    input_array (arr,size);
    print_array (arr,size);
    array_to_matrix(mat, arr, m, n);
    print_matrix(mat, m, n);

    /* free resources */
    free(arr);
    for (i = 0; i < m; ++i)
      free(mat[i]);
    free(mat);

    return 0;
}

void input_array (int *arr,int size)
{
    int i;
    for(i=0;i<size;i++)
    {
        printf("Enter element a[%d]",i);
        if (scanf("%d",&arr[i]) != 1) {
          int c;

          puts("invalid value, redo");

          /* flush invalid value up to the end of line */
          while ((c = getchar()) != '\n') {
            if (c == EOF) {
              puts("EOF, abort");
              exit(-1);
            }
          }

          i -= 1;
        }
    }
}

void print_array (int *arr, int size)
{
    int i;
    printf("\n 1D array is as follows : \n");
    for(i=0;i<size;i++)
    {
        printf("%d ",arr[i]);
    }
}

void array_to_matrix(int ** matrix, int *arr, int row, int col)
{
    int i,j,k=0;     
    for(i=0;i<row;i++)
    {
        for(j=0;j<col;j++)
        {
            matrix[i][j] = arr[k++];
        }
    }

}

void print_matrix(int ** matrix, int row, int col)
{
    int i,j;
    printf("\n 2D matrix is as follows : \n");
    for(i=0;i<row;i++)
    {
        for(j=0;j<col;j++)
        {
            printf("%d ",matrix[i][j]);
        }
        printf("\n");
    }
}

Compilation and execution :

pi@raspberrypi:/tmp $ gcc -g -Wall c.c
pi@raspberrypi:/tmp $ ./a.out
Enter the number of rows(m):2
Enter the number of columns(n):aze
invalid value for columns
pi@raspberrypi:/tmp $ ./a.out
Enter the number of rows(m):-1
invalid value for rows
pi@raspberrypi:/tmp $ ./a.out
Enter the number of rows(m):2
Enter the number of columns(n):3
Enter element a[0]1
Enter element a[1]aa
invalid value, redo
Enter element a[1]2
Enter element a[2]3
Enter element a[3]4
Enter element a[4]5
Enter element a[5]6

 1D array is as follows : 
1 2 3 4 5 6 
 2D matrix is as follows : 
1 2 3 
4 5 6 
pi@raspberrypi:/tmp $