# recursively draw the line

Discussion in 'C Programming' started by Matt, Oct 5, 2003.

1. ### MattGuest

I am writing a recursive program to draw the lines recursively, given the
range[min,max] and number of intervals (n) between the range.

The problem is I don't know how to draw the line in point 0.375, as you see below.

#include <iostream>
using namespace std;

void draw(double min, double max, int n);

int main()
{ draw(0,1,8);
}

void draw(double min, double max, int n)
{ if (n != 1)
{ double mid = (max - min)/2;
cout << mid << endl;
draw(min, mid, n/2);
}
}

The program output:
0.5
0.25
0.125

Here's the expected output:
0.5
0.25
0.125
0.375
0.75
0.625
0.875

Matt, Oct 5, 2003

2. ### Ben PfaffGuest

(Matt) writes:

> I am writing a recursive program to draw the lines recursively, given the
> range[min,max] and number of intervals (n) between the range.

C has no facilities for drawing lines.

> The problem is I don't know how to draw the line in point 0.375, as you see below.

> #include <iostream>

That's not C.

> The program output:
> 0.5
> 0.25
> 0.125

That's not a line. Those are numbers.
--
"What is appropriate for the master is not appropriate for the novice.
You must understand the Tao before transcending structure."
--The Tao of Programming

Ben Pfaff, Oct 5, 2003

3. ### -berlin.deGuest

Matt <> wrote:
> I am writing a recursive program to draw the lines recursively, given the
> range[min,max] and number of intervals (n) between the range.

> The problem is I don't know how to draw the line in point 0.375, as you see below.

> #include <iostream>
> using namespace std;

Sorry, but this a C newsgroup, there's also a C++ group in case you have
problems with C++. So let's replace this with

#include <stdio.h>

> void draw(double min, double max, int n);

> int main()
> { draw(0,1,8);
> }

You forgot to have main() return an int...

> void draw(double min, double max, int n)
> { if (n != 1)
> { double mid = (max - min)/2;

You need to add the starting point of the interval here:

double mid = ( max - min ) / 2 + min;

(the mid-point between e.g. 4 and 5 is 4.5 and not just 0.5).

> cout << mid << endl;

Sorry, this won't work in C, use instead

printf( "%f\n", mid );

> draw(min, mid, n/2);

Now you're "drawing" the lower half of the interval but you forget to
also "draw" the upper half. You need an additional call:

draw( mid, max, n / 2 );

> }
> }

Regards, Jens
--
_ _____ _____
| ||_ _||_ _| -berlin.de
_ | | | | | |
| |_| | | | | | http://www.physik.fu-berlin.de/~toerring
\___/ens|_|homs|_|oerring

-berlin.de, Oct 5, 2003
4. ### Richard HeathfieldGuest

Matt wrote:

> I am writing a recursive program to draw the lines recursively, given the
> range[min,max] and number of intervals (n) between the range.
>
> The problem is I don't know how to draw the line in point 0.375, as you
>
>
> #include <iostream>
> using namespace std;

Try comp.lang.c++

--
Richard Heathfield :
"Usenet is a strange place." - Dennis M Ritchie, 29 July 1999.
C FAQ: http://www.eskimo.com/~scs/C-faq/top.html
K&R answers, C books, etc: http://users.powernet.co.uk/eton

Richard Heathfield, Oct 5, 2003
5. ### Barry SchwarzGuest

On 5 Oct 2003 10:44:13 -0700, (Matt) wrote:

>I am writing a recursive program to draw the lines recursively, given the
>range[min,max] and number of intervals (n) between the range.

snip

different subjects to multiple groups. If you must post to more than
one group, put all the group names on one message.

<<Remove the del for email>>

Barry Schwarz, Oct 5, 2003
6. ### Julian V. NobleGuest

Matt wrote:
>
> I am writing a recursive program to draw the lines recursively, given the
> range[min,max] and number of intervals (n) between the range.
>

Search under Bresenham's Algorithm. Can also be used to draw ellipses ;-)

--
Julian V. Noble
Professor Emeritus of Physics

^^^^^^^^^^^^^^^^^^
http://galileo.phys.virginia.edu/~jvn/

"Science knows only one commandment: contribute to science."
-- Bertolt Brecht, "Galileo".

Julian V. Noble, Oct 6, 2003