printing elements of an array using pointers

zeebo17 · 05-21-2009, 03:16 PM

Hi,

I'm just learning about pointers and as a simple exercise I am trying to print the elements of the array. I'm trying to write a simple function that cycles through the columns and then prints each value to the screen. However, I'm having trouble calling the function properly.

Code:

/*Function the prints a single row array's contents to the screen. */

void  matrix_print(int row, int col, double *m){
  int i;
  for(i=0; i<col; i++){
   
    printf("%d  ",*(m+i*col));
  }
  printf("\n");
}

main(){

  double arr[5] = { 2.5, 3.2, 18.7, -1.35, 4.2 };
  matrix_print(1, 5, *arr[5]);  //causing an error
}

The problem in the 3rd argument to the of the matrix_print. The error says that it is an compatible type. Any suggestions?

Thanks in advance!

ಠ_ಠ · 05-21-2009, 03:43 PM

your function expects a pointer to a double
you are passing in a double (located outside the bounds of arr)

c.user · 05-22-2009, 08:55 PM

Code:

    matrix_print(1, 5, arr);

and

Code:

    for (i = 0; i < col; i++)   
        printf("%g  ",*(m+row*i));
    putchar('\n');

this will print col elements from row (from m)

cas · 05-22-2009, 09:30 PM

You're trying to make pointers more complex than they really are. C scales pointer arithmetic, so you don't need to calculate indices. There are two obvious ways to print out your array:

Code:

#include <stdio.h>

static void f(double *a, int n)
{
  int i;

  for(i = 0; i < n; i++)
  {
    printf("%f ", a[i]);
    /* or slightly less obvious, imo */
    printf("%f ", *(a + i));
  }
  putchar('\n');
}

int main(void)
{
  double a[5] = { 2.5, 3.2, 18.7, -1.35, 4.2 };

  f(a, 5);

  return 0;
}

You can use the array subscript operator (that is, []) on pointers. Arrays and pointers have a close relationship in C, which means that often you can treat them the same way. In fact, the following function declaration:

Code:

void f(double a[]);

is the same as:

Code:

void f(double *a);

Don't get the idea that pointers and arrays are the same thing--they're not--but their relationship is such that you can use the array operator on pointers (and, to tell the truth, you can only use it on pointers, but that's another discussion).

05-21-2009, 03:16 PM	#1
zeebo17 Registered User Join Date: May 2009 Posts: 5	printing elements of an array using pointers Hi, I'm just learning about pointers and as a simple exercise I am trying to print the elements of the array. I'm trying to write a simple function that cycles through the columns and then prints each value to the screen. However, I'm having trouble calling the function properly. Code: /Function the prints a single row array's contents to the screen. / void matrix_print(int row, int col, double m){ int i; for(i=0; i<col; i++){ printf("%d ",(m+icol)); } printf("\n"); } main(){ double arr[5] = { 2.5, 3.2, 18.7, -1.35, 4.2 }; matrix_print(1, 5, arr[5]); //causing an error } The problem in the 3rd argument to the of the matrix_print. The error says that it is an compatible type. Any suggestions? Thanks in advance!
zeebo17 is offline

05-21-2009, 03:43 PM	#2
ಠ_ಠ Banned Join Date: Mar 2009 Posts: 533	your function expects a pointer to a double you are passing in a double (located outside the bounds of arr) __________________ ╔╗╔══╦╗ ║║║╔╗║║ ║╚╣╚╝║╚╗ ╚═╩══╩═╝
ಠ_ಠ is offline

05-22-2009, 08:55 PM	#3
c.user Registered User Join Date: Apr 2009 Location: Russia Posts: 116	Code: matrix_print(1, 5, arr); and Code: for (i = 0; i < col; i++) printf("%g ",(m+rowi)); putchar('\n'); this will print col elements from row (from m)
c.user is offline

05-22-2009, 09:30 PM	#4
cas Registered User Join Date: Sep 2007 Posts: 372	You're trying to make pointers more complex than they really are. C scales pointer arithmetic, so you don't need to calculate indices. There are two obvious ways to print out your array: Code: #include <stdio.h> static void f(double a, int n) { int i; for(i = 0; i < n; i++) { printf("%f ", a[i]); / or slightly less obvious, imo / printf("%f ", (a + i)); } putchar('\n'); } int main(void) { double a[5] = { 2.5, 3.2, 18.7, -1.35, 4.2 }; f(a, 5); return 0; } You can use the array subscript operator (that is, []) on pointers. Arrays and pointers have a close relationship in C, which means that often you can treat them the same way. In fact, the following function declaration: Code: void f(double a[]); is the same as: Code: void f(double *a); Don't get the idea that pointers and arrays are the same thing--they're not--but their relationship is such that you can use the array operator on pointers (and, to tell the truth, you can only use it on pointers, but that's another discussion).
cas is offline

Thread Tools
Show Printable Version Email this Page
Display Modes
Linear Mode Switch to Hybrid Mode Switch to Threaded Mode

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
Dynamic array of structures containing yet another dynamic array of structures	innqubus	C Programming	2	07-11-2008 07:39 AM
using realloc for a dynamically growing array	broli86	C Programming	10	06-27-2008 05:37 AM
Syntax for constant array of array pointers	BMintern	C Programming	4	05-14-2008 08:21 AM
Is there a way to find the number of elements in an array?	lime	C Programming	2	08-03-2003 10:01 AM
how to create a linked list of items using pointers stored in a two dimensional array	Unregistered	C Programming	5	11-20-2001 12:48 PM