(C) + + Table Structure

**willi** · 11-16-2009, 11:50 AM

Hello, I started in C + + and I want to make a table structure
I do this:
* body = new body tableau_de_corp [N]

With body is poised of structures coordinates (x, y) describes the acceleration, velocity as well as position of a tip.

Code:

1.	# include <iostream>
2.	
3.	
4.	# include <cmath>
5.	# define G 6.67E-11
6.	# define N 2
7.	using namespace std;
8.	
9.	
10.	
11.	
12.	struct Coordonnees
13.	(
14.	float x;
15.	float y;
16.	);
17.	
18.	struct body (
19.	float mass;
20.	Position coordinates;
21.	Coordinates speed;
22.	Acceleration coordinates;
23.	
24.	);
25.	
26.	calcul_acceleration void (* tableau_de_corps body = new body [2])
27.	(
28.	* Coordinates = new tableau_de_acc Coordonnees [N];
29.	for (int i = 0; i <(N-1) i + +)
30.	(
31.	tableau_de_acc [i]. x = (tableau_de_corps [i +1]. mass) * ((tableau_de_corps [i +1]. (position)). x - (tableau_de_corps [i]. (position)). x) / abs ( pow (norm (tableau_de_corps [i]. (position). tableau_de_corps-x [i +1]. (position). x, 3));
32.	tableau_de_acc [i]. y = (tableau_de_corps [i +1]. mass) * ((tableau_de_corps [i +1]. (position)). y - (tableau_de_corps [i]. (position)). y) / abs ( pow (norm (tableau_de_corps [i]. (position). tableau_de_corps-y [i +1]. (position). y, 3));
33.	court <<tableau_de_acc [i] <<endl;
34.	
35.	)
36.	tableau_de_acc [i]. y *= G
37.	tableau_de_acc [i]. x *= G
38.	)
39.	
40.	
41.	float norm (coordinated vector)
42.	(
43.	float n = sqrt (pow (vecteur.x, 2) + pow (vecteur.y, 2));
44.	return n;
45.	)
46.	
47.	
48.	
49.	int main ()
50.	(
51.	tableau_de_corps * body = new body [N] / / No creation of body
52.	
53.	calcul_acceleration (tableau_de_corps []);
54.	return 0;55.	)

My trouble lies in the void calcul_acceleration. If for instance in the first box and there is a body, I want to alter some of the details of the acceleration, should I write:

Code:

1.	(tableau_de_corps [i +1]. (position)). x

or

Code:

1.	(tableau_de_corps [i +1] -> (position)). x

Or something else?

Thank you in advance

**gorden** · 11-16-2009, 11:52 AM

I read a course on std: vector. So I change my old vector table. That said, I still have the problem with the syntax:

(tableau_de_corps [i +1]. (position)). x

Thank you.

**chreshel** · 11-16-2009, 11:53 AM

eneleve your brackets they are useless.

**aldrin** · 11-16-2009, 11:55 AM

Okay great!

Almost everything works, I have no error in the formula, cons by something blocking the main ():

Code:

1.	# include <vector>
2.	# include <iostream>
3.	# include <cmath>
4.	# define G 6.67E-11
5.	# define N 2
6.	using namespace std;
7.	
8.	
9.	struct Coordonnees
10.	(
11.	float x;
12.	float y;
13.	);
14.	
15.	struct body (
16.	float mass;
17.	Position coordinates;
18.	Coordinates speed;
19.	Acceleration coordinates;
20.	
21.	);
22.	
23.	Coordinates operator - (coordinates a, b Coordonnees)
24.	(
25.	Coordinates res;
26.	res.x = ax-bx;
27.	res.y = ay-by;
28.	return res;
29.	)
30.	
31.	float norm (vector Coordonnees)
32.	(
33.	float n = sqrt (pow (vecteur.x, 2) + pow (vecteur.y, 2));
34.	return n;
35.	)
36.	
37.	
38.	calcul_acceleraton void (vector <body> tableau_de_corps)
39.	(
40.	* Coordinates = new tableau_de_acc Coordonnees [N];
41.	int i = 0;
42.	for (i, i <(N-1) i + +)
43.	(
44.	tableau_de_acc [i]. x = (tableau_de_corps [i +1]. mass) * (tableau_de_corps [i +1]. position.x);
45.	tableau_de_acc [i]. x = (tableau_de_corps [i +1]. mass) * (tableau_de_corps [i +1]. position.x - tableau_de_corps [i]. position.x) / abs (pow (norm (tableau_de_corps [i] . tableau_de_corps-position [i +1]. position), 3));
46.	tableau_de_acc [i]. y = (tableau_de_corps [i +1]. mass) * (tableau_de_corps [i +1]. position.y - tableau_de_corps [i]. position.y) / abs (pow (norm (tableau_de_corps [i] . tableau_de_corps-position [i +1]. position), 3));
47.	court <<tableau_de_acc [i]. x <<endl;
48.	
49.	)
50.	tableau_de_acc [i]. y *= G;
51.	tableau_de_acc [i]. x *= G;
52.	)
53.	
54.	
55.	
56.	int main ()
57.	(
58.	vector <corps*> liste_corps / / No creation of body
59.	calcul_acceleraton (vector liste_corps) Missing template arguments before 'liste_corps'
60.	return 0;61.	)

Missing template arguments before 'liste_corps' on the line calling the function calcul_acceleration
Voila, thank you, I think (hope) that it will be the last question.

PS: I still have a second concern, I have tried to

Code:

1.	liste_corps [1]. position.x = 1;

I put the following error:

Code:

1.	error: request for member 'position' in 'liste_corps. std:: vector <_Tp, _Alloc>:: operator [] [with _Tp = body *, _Alloc = std:: allocator <corps*>] (1UL) 'Which is of non-class type' body * '

**joshin** · 11-16-2009, 11:57 AM

Yes. I repeat:

you make a vector <corps*> so you create an array of pointers, but nothing sets. You have a vector Besin <body> (and this time leave it. Position).

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