Why Use a Helper Variable When Inserting an Element in an Array?

  • MHB
  • Thread starter mathmari
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In Summary, We had defined StarS[N] to be an array of lists.)In summary, the programmer wants to write a function for the constitution of a star system. They are wondering how they can insert an element in an array in time complexity O(1). They also want to know what variables they need to use to achieve this. They have done some research and found that setting an element in an "normal" array at a certain index to a value is an O(1) operation, and inserting an element in a linked list (if you already know the location) is also an O(1) operation. They want to write a program for the constitution of a star system "ss". They have also defined
  • #71
mathmari said:
Code: 
		else{
			ast->next=last->next;
			ast->prev=last;
			last->next=ast;
			ast->gap=ast->gap-g;
			q=ast->next;
			q->gap=q->gap-ast->gap;	
	    }

Is it correct?? (Wondering)

Almost there! (Smile)

In the regular case, 4 connections need to be made (2 next, 2 prev).
I only see 3 connections. (Wasntme)
 
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  • #72
I like Serena said:
Almost there! (Smile)

In the regular case, 4 connections need to be made (2 next, 2 prev).
I only see 3 connections. (Wasntme)

Do I have to add [m]last->next->prev=ast[/m] ?? (Wondering)

I made some more changes at the else-statement.

Code: 
    else{
                asteroid_t *last=p->asteroids;
                asteroid_t *q=NULL;
                asteroid_t *previous=NULL;
                if(ast->gap<last->gap){
                        ast->prev=NULL;
                        ast->next=last;
                        last->prev=ast;
                        last->gap=last->gap-ast->gap;
                }
                else{
                while(g < ast->gap && last != NULL && last->next != NULL){
	                	g=g+last->gap;
	                	previous=last;
                                last=last->next;
                }
                if(last != NULL && last->next==NULL){
                        ast->prev=last;
                        ast->next=NULL;
                        last->next=ast;
                        ast->gap=ast->gap-g;
                }
                else if(last == NULL){
	                	previous->next=ast;
	                	ast->prev=previous;
	                	ast->next=NULL;
	                	ast->gap = ast->gap - previous->gap;
                }    
                else{
                        ast->next=last->next;
                        last->next->prev=ast;
                        ast->prev=last;
                        last->next=ast;
                        ast->gap=ast->gap-g;
                        q=ast->next;
                        q->gap=q->gap-ast->gap;
            }
        }
    }

When I add the first asteroid ( for example "as"=1, "gap"=10 ) it prints the correct gap.

When I add then a second asteroid ( for example "as"=2, "gap"=25 ) it prints as the gap 25, which is the gap between the asteroid "as"=2 and the object "solid"=101 but it should print the gap between this asteroid "as"=2 and the previous one of the list, which is "as"=1.

Have I done something wrong at the calculation of the gap?? (Wondering)
 
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  • #73
I changed the while and now it prints 15, which is the gap between the "as"=1 ans the "as"=2 instead of 25!

Code: 
while(g < ast->gap && last->next != NULL){
	                g=g+last->gap;
                        last=last->next;
                }
                g=g+last->gap;
(Happy)
 
  • #74
mathmari said:
Do I have to add [m]last->next->prev=ast[/m] ?? (Wondering)

Yes.
And I see you did! (Smile)

When I add the first asteroid ( for example "as"=1, "gap"=10 ) it prints the correct gap.

When I add then a second asteroid ( for example "as"=2, "gap"=25 ) it prints as the gap 25, which is the gap between the asteroid "as"=2 and the object "solid"=101 but it should print the gap between this asteroid "as"=2 and the previous one of the list, which is "as"=1.

Have I done something wrong at the calculation of the gap?? (Wondering)

mathmari said:
I changed the while and now it prints 15, which is the gap between the "as"=1 ans the "as"=2 instead of 25!

Code: 
while(g < ast->gap && last->next != NULL){
	                g=g+last->gap;
                        last=last->next;
                }
                g=g+last->gap;
(Happy)

So your gap calculations are okay now? (Wondering)
 
  • #75
I like Serena said:
So your gap calculations are okay now? (Wondering)

Yes! (Yes)(Happy)Now I have to write also an other function. (Nerd)

I have to write a function for the destruction of the planetary system "solid".
With the destruction of the planetary system, the asteroids where the gap between this one and the object, is at least "gap" will also be destructed. (so, they have to be deleted) The asteroids for which the gap is greater are converted to free-floating planets consisting a new collection of free-floating planets (ffplan_t). This new collection should be added to the array of the free-floating planets of the star system to which the planetary system, that is destructed, belonged. The identifier "fp" of the new collection is the identifier of the planetary system that is destructed. The list of the free-floating planets that corresponds to the new collection should be sorted as for the field "as" of the asteroids that are contained. The destructed planetary system should be deleted from the list of planetary systems of the star system to which it belonged.I have done the following:

Code: 
int destruction(int solid, int gap){
	int sum=0;
	plansys_t *p=StarS[0].plasy;;
	for(i=0; i<nrStarS; i++){
		p=StarS[i].plasy;
		while (p != NULL && p->solid != solid){
			p=p->next;
		}
	}
	if(p == NULL){
		printf("The planetary system with identifier %d couldn't be found\n", solid);
	}
	asteroid_t *f=p->asteroids;
	while(sum<gap){
		sum=sum+f->gap;
		DELETE(f, as);
		f=f->next;
	}
	
	

	return 0;
}

where the function DELETE() is the following:

Code: 
void DELETE(*pointer, int x){
	while(pointer != NULL && pointer->data != x)
		pointer=pointer->next;
	if(pointer == NULL)
		printf("Element %d is not present in the list\n", d);
	if(pointer->prev == NULL && pointer->next != NULL){
		(pointer->next).prev=NULL;
	}
	if(pointer->prev == NULL && pointer->next==NULL){
		pointer=NULL;
	}
	if(pointer->prev != NULL && pointer->next==NULL){
		(pointer->prev).next=NULL;
	}
	else{
		(pointer->prev).next=pointer.next;
		(pointer->next).prev=pointer.prev;
	}
}

Is it correct so far?? (Wondering)
The asteroids for which the gap is greater that "gap" are converted to free-floating planets consisting a new collection of free-floating planets (ffplan_t).

What am I supposed to do at this step?? (Wondering) I got stuck right now...
 
  • #76
The asteroids for which the gap is greater that "gap" are converted to free-floating planets consisting a new collection of free-floating planets (ffplan_t).

Does this mean that I have to insert these asteroids to the list of the free-floating planets?? (Wondering)
 
  • #77
mathmari said:
Code: 
void DELETE(*pointer, int x){
	while(pointer != NULL && pointer->data != x)
		pointer=pointer->next;
	if(pointer == NULL)
		printf("Element %d is not present in the list\n", d);
	if(pointer->prev == NULL && pointer->next != NULL){
		(pointer->next).prev=NULL;
	}
	if(pointer->prev == NULL && pointer->next==NULL){
		pointer=NULL;
	}
	if(pointer->prev != NULL && pointer->next==NULL){
		(pointer->prev).next=NULL;
	}
	else{
		(pointer->prev).next=pointer.next;
		(pointer->next).prev=pointer.prev;
	}
}

Is it correct so far?? (Wondering)

That looks a bit complicated, and the memory allocated for the pointer (with calloc) is not actually freed.

How about:
Code: 
void DELETE(asteroid_t *pointer, int x){
	while(pointer != NULL && pointer->data != x) {
		pointer=pointer->next;
        }
	if(pointer == NULL) {
		printf("Element %d is not present in the list\n", d);
		return;
        } 
	if(pointer->next != NULL){
		pointer->next->prev=pointer->prev;
	}
	if(pointer->prev != NULL){
		pointer->prev->next = pointer->next;
	}
        free(pointer);
}
(Wondering)

mathmari said:
Does this mean that I have to insert these asteroids to the list of the free-floating planets?? (Wondering)

That appears to be the case. (Wink)
 
  • #78
I like Serena said:
That looks a bit complicated, and the memory allocated for the pointer (with calloc) is not actually freed.

How about:
Code: 
void DELETE(asteroid_t *pointer, int x){
	while(pointer != NULL && pointer->data != x) {
		pointer=pointer->next;
        }
	if(pointer == NULL) {
		printf("Element %d is not present in the list\n", d);
		return;
        } 
	if(pointer->next != NULL){
		pointer->next->prev=pointer->prev;
	}
	if(pointer->prev != NULL){
		pointer->prev->next = pointer->next;
	}
        free(pointer);
}
(Wondering)

I see! (Nerd)
I like Serena said:
That appears to be the case. (Wink)

The asteroids for which the gap is greater are converted to free-floating planets consisting a new collection of free-floating planets (ffplan_t). This new collection should be added to the array of the free-floating planets of the star system to which the planetary system, that is destructed, belonged. The identifier "fp" of the new collection is the identifier of the planetary system that is destructed. The list of the free-floating planets that corresponds to the new collection should be sorted as for the field "as" of the asteroids that are contained. The field "gap" of the new list should have the value 0

I tried to insert the asteroids, for which the gap is greater than "gap", to the list of the free-floating planets as followed:

Code: 
ffplan_t *fplan=NULL;
	if(f != NULL){
		fplan->fp=solid;
	}
	asteroid_t *planf = calloc(1, sizeof(asteroid_t));
	planf->as=f->as;
	planf->gap=0;
	planf->next=NULL;
	planf->prev=NULL;
	asteroids *K=fplan->ff;
	f-f->next;
	while(f != NULL){
		if (K == NULL) {
        	K = planf;
        } else {
        	asteroid_t *last = K;
        	while (last->next != NULL) {
        		last = last->next;
        	}
        	last->next = planf;
       	}              
		f=f->next;
	}

Is it correct so far?? (Wondering)
 
  • #79
At the following part there must be an error, since I get a segmentation fault, but when I make this part into comments, I don't get any more...

Code: 
ffplan_t *fplan=NULL;
	if(f != NULL){
		fplan->fp=solid;
	}
	asteroid_t *planf = calloc(1, sizeof(asteroid_t));
	planf->as=f->as;
	planf->gap=0;
	planf->next=NULL;
	planf->prev=NULL;
	asteroid_t *K=fplan->ff;
	f-f->next;
	while(f != NULL){
		if (K == NULL) {
        	K = planf;
        } else {
        	asteroid_t *last = K;
        	while (last->next != NULL) {
        		last = last->next;
        	}
        	last->next = planf;
       	}              
		f=f->next;
	}

Could you tell me what I have done wrong?? (Wondering)
 
  • #80
mathmari said:
At the following part there must be an error, since I get a segmentation fault, but when I make this part into comments, I don't get any more...

Code: 
ffplan_t *fplan=NULL;
	if(f != NULL){
		fplan->fp=solid;
	}
	asteroid_t *planf = calloc(1, sizeof(asteroid_t));
	planf->as=f->as;
	planf->gap=0;
	planf->next=NULL;
	planf->prev=NULL;
	asteroid_t *K=fplan->ff;
	f-f->next;
	while(f != NULL){
		if (K == NULL) {
        	K = planf;
        } else {
        	asteroid_t *last = K;
        	while (last->next != NULL) {
        		last = last->next;
        	}
        	last->next = planf;
       	}              
		f=f->next;
	}

Could you tell me what I have done wrong?? (Wondering)

Well...
You write
Code: 
ffplan_t *fplan=NULL;
	if(f != NULL){
		fplan->fp=solid;
	}
Now I'm not sure what "fplan" and "f" are representing.
Perhaps you can clarify? (Wondering)

Either way, if [m]f != NULL[/m], then the code code assigns "solid" to [m]fplan->fp[/m]... but at this point [m]fplan[/m] is NULL. :eek:
So that would give a segmentation fault. (Crying)
 
  • #81
I like Serena said:
Well...
You write
Code: 
ffplan_t *fplan=NULL;
	if(f != NULL){
		fplan->fp=solid;
	}
Now I'm not sure what "fplan" and "f" are representing.
Perhaps you can clarify? (Wondering)

"f" is a pointer that points to the list p->asteroids

[m]asteroid_t *f=p->asteroids;[/m]
The asteroids for which the gap is greater are converted to free-floating planets consisting a new collection of free-floating planets (ffplan_t). This new collection should be added to the array of the free-floating planets of the star system to which the planetary system, that is destructed, belonged. The identifier "fp" of the new collection is the identifier of the planetary system that is destructed.
We want to add the asteroids, where the "gap" is greater than gap, to the list of free-floating planets.
That's why I used the pointer "fplan". (Tmi)
I like Serena said:
Either way, if [m]f != NULL[/m], then the code code assigns "solid" to [m]fplan->fp[/m]... but at this point [m]fplan[/m] is NULL. :eek:
So that would give a segmentation fault. (Crying)

How can I insert these asteroids to the list of free-floating planets?? (Wondering)
 
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  • #82

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  • #83
I like Serena said:
It should be: [m]starsystem->plasy=starsystem->Sentinel;[/m].

I am looking again at the program and I have a question... (Nerd)

Code: 
int Initialization() {
	int i;
	for(i=0; i<N; i++){
		StarS[i].ss=INT_MAX;
		StarS[i].plasy=NULL;
		StarS[i].ffplan[i].fp=INT_MAX;
		StarS[i].ffplan[i].ff=NULL;
		StarS[i].Sentinel=NULL;
	}
	return 0;
}
int Constitution(int ss) {
1.        int i;
2.        starsy_t *starsystem;
        
3.        if(Sfreep<N){
4.        	starsystem = &StarS[Sfreep];
5.        	Sfreep++;
6.		}
		
7.		if(Sfreep>=N){
8.			return -1;
9.		}
        
10.        starsystem->ss = ss;
11.        starsystem->plasy=starsystem->Sentinel;
12.	for(i=0; i<max; i++){
13.		starsystem->ffplan[i].fp=INT_MAX;
14.		starsystem->ffplan[i].ff=NULL;
15.	}
16.	return (Sfreep - 1);
17.}
At the line 11 of the function Constitution() we set [m]starsystem->plasy=starsystem->Sentinel;[/m] but at the function Initialization() we set [m]StarS.Sentinel=NULL;[/m].

Should we maybe change the value of [m]starsystem->Sentinel[/m] in the function Constitution()?? (Wondering)
Because in that way we set [m]starsystem->plasy[/m] to [m]NULL[/m].
 
  • #84
mathmari said:
I am looking again at the program and I have a question... (Nerd)

Code: 
int Initialization() {
		StarS[i].ffplan[i].fp=INT_MAX;
		StarS[i].ffplan[i].ff=NULL;
}

Let's start with this. (Worried)
There should be a nested loop to iterate over [m]ffplan[/m], for instance with the index [m]j[/m].
Otherwise, we're not initializing everything, and moreover, we'll likely get an access violation. (Devil)
Code: 
int Constitution(int ss) {
11.        starsystem->plasy=starsystem->Sentinel;
17.}

At the line 11 of the function Constitution() we set [m]starsystem->plasy=starsystem->Sentinel;[/m] but at the function Initialization() we set [m]StarS.Sentinel=NULL;[/m].

Should we maybe change the value of [m]starsystem->Sentinel[/m] in the function Constitution()?? (Wondering)
Because in that way we set [m]starsystem->plasy[/m] to [m]NULL[/m].


Yep.
The [m]Sentinel[/m] is handled the wrong way. (Worried)
It is supposed to be a pointer to the last element in the list, which initially does not exist.

We should set both [m]plasy[/m] and [m]Sentinel[/m] to [m]NULL[/m] (or leave them as NULL). (Wasntme)
 
  • #85
I like Serena said:
Let's start with this. (Worried)
There should be a nested loop to iterate over [m]ffplan[/m], for instance with the index [m]j[/m].
Otherwise, we're not initializing everything, and moreover, we'll likely get an access violation. (Devil)

You're right! (Tmi)

So, is it as followed??

Code: 
int Initialization() {
	int i, j;
	for(i=0; i<N; i++){
		StarS[i].ss=INT_MAX;
		StarS[i].plasy=NULL;
		for(j=0; j<max; j++){
			StarS[i].ffplan[i].fp=INT_MAX;
			StarS[i].ffplan[i].ff=NULL;
		}
		StarS[i].Sentinel=NULL;
	}
	return 0;
}

(Wondering)
I like Serena said:
Yep.
The [m]Sentinel[/m] is handled the wrong way. (Worried)
It is supposed to be a pointer to the last element in the list, which initially does not exist.

We should set both [m]plasy[/m] and [m]Sentinel[/m] to [m]NULL[/m] (or leave them as NULL). (Wasntme)

Should it be as followed?? (Wondering)

Code: 
int Constitution(int ss) {
        int i;
        starsy_t *starsystem;
        
        if(Sfreep<N){
        	starsystem = &StarS[Sfreep];
        	Sfreep++;
		}
		
		if(Sfreep>=N){
			return -1;
		}
        
        starsystem->ss = ss;
        starsystem->plasy=NULL;
        starsystem->Sentinel=NULL;
	for(i=0; i<max; i++){
		starsystem->ffplan[i].fp=INT_MAX;
		starsystem->ffplan[i].ff=NULL;
	}
	return (Sfreep - 1);
}

At which point do we change its value so that it points to the last element in the list?? (Wondering)
 
  • #86
mathmari said:
You're right! (Tmi)

So, is it as followed?? (Wondering)

Yep! Much better! (Happy)
Should it be as followed?? (Wondering)

Yep! (Wink)
At which point do we change its value so that it points to the last element in the list?? (Wondering)

Whenever we add an element, or remove an element, we need to take into account that [m]plasy[/m], [m]Sentinal[/m], or both need to be updated. (Sweating)
 
  • #87
I like Serena said:
Whenever we add an element, or remove an element, we need to take into account that [m]plasy[/m], [m]Sentinal[/m], or both need to be updated. (Sweating)

Do you mean for example at the following function??

Code: 
int Beginning(int solid, int ss){
		int i, k=-1;
        /* Add a planetary system to the list of the planetary system of the star system */
        plansys_t *plansystem = calloc(1, sizeof(plansys_t));
        
        plansystem->solid=solid;
        plansystem->asteroids=NULL;
        plansystem->next=NULL;
		for(i=0; i<Sfreep; i++){
			if(StarS[i].ss==ss){
				k=i;
				if (StarS[k].plasy == NULL) {
                     /* List is empty: replace with new plansystem */
                     StarS[k].plasy = plansystem;
                } else {
                    /* Find last node */
                    plansys_t *last = StarS[k].plasy;
                    while (last->next != NULL) {
                          last = last->next;
                    }
                    /* Append new plansystem to the last node */
                    last->next = plansystem;
                    /* last->next->next=last; */
               }
               [COLOR="#FF0000"]StarS[k].Sentinel=StarS[k].plasy;[/COLOR]
			}
		}
		return k;
}

(Wondering)
 
  • #88
mathmari said:
Code: 
int Beginning(int solid, int ss){
    ...
			if(StarS[i].ss==ss){
				k=i;
				if (StarS[k].plasy == NULL) {
                     /* List is empty: replace with new plansystem */
                     StarS[k].plasy = plansystem;
                } else {
                    /* Find last node */
                    plansys_t *last = StarS[k].plasy;
                    while (last->next != NULL) {
                          last = last->next;
                    }
                    /* Append new plansystem to the last node */
                    last->next = plansystem;
                    /* last->next->next=last; */
               }
               [COLOR="#FF0000"]StarS[k].Sentinel=StarS[k].plasy;[/COLOR]
			}

Almost... (Thinking)

Now you are always setting the Sentinal to the first node, but it should be the last node. (Wasntme)

Hmm, it would help if there were some consistency to the indentation... (Wink)
 
  • #89
I like Serena said:
Almost... (Thinking)

Now you are always setting the Sentinal to the first node, but it should be the last node. (Wasntme)

Is it maybe as followed??

Code: 
int Beginning(int solid, int ss){
		int i, k=-1;
        /* Add a planetary system to the list of the planetary system of the star system */
        plansys_t *plansystem = calloc(1, sizeof(plansys_t));
        
        plansystem->solid=solid;
        plansystem->asteroids=NULL;
        plansystem->next=NULL;
		for(i=0; i<Sfreep; i++){
			if(StarS[i].ss==ss){
				k=i;
				if (StarS[k].plasy == NULL) {
                     /* List is empty: replace with new plansystem */
                     StarS[k].plasy = plansystem;
                     [COLOR="#FF0000"]StarS[k].Sentinel=StarS[k].plasy;[/COLOR]
                } else {
                    /* Find last node */
                    plansys_t *last = StarS[k].plasy;
                    while (last->next != NULL) {
                          last = last->next;
                    }
                    /* Append new plansystem to the last node */
                    last->next = plansystem;
                    [COLOR="#FF0000"]last->next->Sentinel=last;[/COLOR]
               }
			}
		}
		return k;
}

(Wondering)

I like Serena said:
Hmm, it would help if there were some consistency to the indentation... (Wink)

What do you mean?? (Wondering)
 
  • #90
mathmari said:
Is it maybe as followed?? (Wondering)

The first is correct! (Smile)

But the second is not. (Worried)
Sentinal is a data member of StarS[k], and not of last->next.
You should set StarS[k].Sentinal to last->next, which is by now the same as plansystem.Alternatively, you could do at the end: [m]StarS[k].Sentinal = plansystem[/m].
That works because [m]plansystem[/m] is always added to the end, wherever that is. So afterwards it is the last node in the list, which is where [m]Sentinal[/m] should point. (Nerd)
What do you mean?? (Wondering)

The way the code is indented, it is hard to follow the flow of the program, and understand if and where something is wrong and should be changed. (Sweating)

Better is:
Code: 
int Beginning(int solid, int ss){
    int i, k = -1;
    /* Add a planetary system to the list of the planetary system of the star system */
    plansys_t *plansystem = calloc(1, sizeof(plansys_t));
    
    plansystem->solid = solid;
    plansystem->asteroids = NULL;
    plansystem->next = NULL;
    for(i=0; i<Sfreep; i++){
        if(StarS[i].ss == ss){
            k=i;
            if (StarS[k].plasy == NULL) {
                /* List is empty: replace with new plansystem */
                StarS[k].plasy = plansystem;
                StarS[k].Sentinel = StarS[k].plasy;
            } else {
                /* Find last node */
                plansys_t *last = StarS[k].plasy;
                while (last->next != NULL) {
                    last = last->next;
                }
                /* Append new plansystem to the last node */
                last->next = plansystem;
                last->next->Sentinel = last;
            }
        }
    }
    return k;
}

Like this it becomes clear where the for-loop starts and ends, where the first if-statement is, and where the nested if-else statement is (and that there is one). (Whew)
 
  • #91
I like Serena said:
The first is correct! (Smile)

But the second is not. (Worried)
Sentinal is a data member of StarS[k], and not of last->next.
You should set StarS[k].Sentinal to last->next, which is by now the same as plansystem.Alternatively, you could do at the end: [m]StarS[k].Sentinal = plansystem[/m].
That works because [m]plansystem[/m] is always added to the end, wherever that is. So afterwards it is the last node in the list, which is where [m]Sentinal[/m] should point. (Nerd)

Do you mean that we could write it as followed??

Code: 
int Beginning(int solid, int ss){
        int i, k=-1;
        /* Add a planetary system to the list of the planetary system of the star system */
        plansys_t *plansystem = calloc(1, sizeof(plansys_t));
        
        plansystem->solid=solid;
        plansystem->asteroids=NULL;
        plansystem->next=NULL;
	for(i=0; i<Sfreep; i++){
		if(StarS[i].ss==ss){
			k=i;
			if (StarS[k].plasy == NULL) {
                                   /* List is empty: replace with new plansystem */
                                   StarS[k].plasy = plansystem;
                        } else {
                                    /* Find last node */
                                    plansys_t *last = StarS[k].plasy;
                                    while (last->next != NULL) {
                                             last = last->next;
                                    }
                                    /* Append new plansystem to the last node */
                                    last->next = plansystem;
                        }
                        [COLOR="#FF0000"]StarS[k].Sentinal = plansystem;[/COLOR]
                }
        }
	return k;
}

(Wondering)
I like Serena said:
The way the code is indented, it is hard to follow the flow of the program, and understand if and where something is wrong and should be changed. (Sweating)

Better is:
Code: 
int Beginning(int solid, int ss){
    int i, k = -1;
    /* Add a planetary system to the list of the planetary system of the star system */
    plansys_t *plansystem = calloc(1, sizeof(plansys_t));
    
    plansystem->solid = solid;
    plansystem->asteroids = NULL;
    plansystem->next = NULL;
    for(i=0; i<Sfreep; i++){
        if(StarS[i].ss == ss){
            k=i;
            if (StarS[k].plasy == NULL) {
                /* List is empty: replace with new plansystem */
                StarS[k].plasy = plansystem;
                StarS[k].Sentinel = StarS[k].plasy;
            } else {
                /* Find last node */
                plansys_t *last = StarS[k].plasy;
                while (last->next != NULL) {
                    last = last->next;
                }
                /* Append new plansystem to the last node */
                last->next = plansystem;
                last->next->Sentinel = last;
            }
        }
    }
    return k;
}

Like this it becomes clear where the for-loop starts and ends, where the first if-statement is, and where the nested if-else statement is (and that there is one). (Whew)

Ok! (Blush)
 
  • #92
mathmari said:
Do you mean that we could write it as followed?? (Wondering)

Yep! (Nod)
 
  • #93
mathmari said:
The structures have the following form:

View attachment 3540

I am looking again at the program and I got stuck...

Code: 
asteroid_t *p=StarS[k].plasy->asteroids;
while(p != NULL && p->as != as){
		p=p->next;
}
if(p != NULL && p->as == as){
		k=i;				
}
After [m]p=p->next;[/m] where does [m]p[/m] point?? At the next node of the planetary system, plasy, or the next asteroid?? (Wondering)
 
  • #94
Hey! :eek:

mathmari said:
After [m]p=p->next;[/m] where does [m]p[/m] point?? At the next node of the planetary system, plasy, or the next asteroid?? (Wondering)

Code: 
asteroid_t *p=StarS[k].plasy->asteroids;

After the initial assignment, [m]p[/m] points to the first asteroid of the first planetary system of star system [m]k[/m].

Code: 
while(p != NULL && p->as != as){
		p=p->next;
}

After p=p->next, p points to the next asteroid of the first planetary system. (Nerd)
 
  • #95
Ok! (Malthe)

To find the asteroid with identifier "as" in the star system I had written the following part:

Code: 
	int i, k=-1;
	asteroid_t *p=NULL;
	asteroid_t *ast=NULL;
	for(i=0; i<Sfreep; i++){
			ast=StarS[i].plasy->asteroids;
			while(ast != NULL && ast->as != as){
				ast=ast->next;
			}
			if(ast != NULL && ast->as == as){
				k=i;				
			}
	}

	if(k == -1){
		return -1;
	}
		
	p=StarS[k].plasy->asteroids;
	
	if(p == NULL){
		return -1;
	}

But in this way do we not look only the asteroids of the first planetary system?? (Wondering)

Should it be as followed??

Code: 
	for(i=0; i<Sfreep; i++){
                        Plan_Syst=StarS[i].plasy;
                        while(Plan_Syst != NULL){ 
                                ast=Plan_Syst->asteroids;
			        while(ast != NULL && ast->as != as){
				        ast=ast->next;
			        }
			        if(ast != NULL && ast->as == as){
				        k=i;	
                                        A=ast;			
			       }
                               Plan_Syst=Plan_Syst->next; 
	                }
        }
	if(k == -1){
		return -1;
	}
		
	p=A;
	
	if(p == NULL){
		return -1;
	}

(Wondering)
 
  • #96
mathmari said:
Ok! (Malthe)

But in this way do we not look only the asteroids of the first planetary system?? (Wondering)

Should it be as followed??

(Wondering)

Yep. To search all asteroids it should be like that. (Wasntme)
 
  • #97
I like Serena said:
Yep. To search all asteroids it should be like that. (Wasntme)

Ok! (Malthe) I have also an other question...
I like Serena said:
Code: 
int nrStarS = 0;

int Constitution(int ss) {
        int i;

        // Add a star system to the the array of stars
        [COLOR="#FF0000"]starsy_t *starsystem = &StarS[nrStarS];[/COLOR]
        nrStarS++;

        // Initialize the new star system
        starsystem->ss = ss;
        starsystem->plasy=StarS[i].Sentinel;
	for(i=0; i<max; i++){
		starsystem->ffplan[i].fp=INT_MAX;
		starsystem->ffplan[i].ff=NULL;
	}

        // Return the index of the star system that was added
	return (nrStarS - 1);
}

int main(){
	Constitution(12);
	for(i=0; i<nrStarS; i++){
		printf("The elements are: %d \n", StarS[i].ss);
	}
	return 0;
}

Could you explain to me why we write [m]starsystem = &StarS[nrStarS];[/m] and not [m]&StarS[nrStarS]=starsystem[/m] ?? (Wondering)
 
  • #98
mathmari said:
Could you explain to me why we write [m]starsystem = &StarS[nrStarS];[/m] and not [m]&StarS[nrStarS]=starsystem[/m] ?? (Wondering)

The structure [m]StarS[nrStarS][/m] is an entry in a global array. Its address is fixed and cannot change. That means it makes no sense to try and assign anything to [m]&StarS[nrStarS][/m].

The pointer [m]starsystem[/m] is a helper variable. We let it point to the location of [m]StarS[nrStarS][/m], so that we can manipulate it more easily, and so that the code reads better. That's why we assign the address [m]&StarS[nrStarS][/m] to it. (Nerd)
 
  • #99
I like Serena said:
The structure [m]StarS[nrStarS][/m] is an entry in a global array. Its address is fixed and cannot change. That means it makes no sense to try and assign anything to [m]&StarS[nrStarS][/m].

The pointer [m]starsystem[/m] is a helper variable. We let it point to the location of [m]StarS[nrStarS][/m], so that we can manipulate it more easily, and so that the code reads better. That's why we assign the address [m]&StarS[nrStarS][/m] to it. (Nerd)

How can the array [m]StarS[/m] have the value of the new starsystem at the position nrStarS, when we assign the [m]&StarS[nrStarS][/m] to [m]starsystem[/m] ?? (Wondering)

[m]nrStarS[/m] is the first free position of the array, so if we assign [m]&StarS[nrStarS][/m] to the new [m]starsystem[/m] doesn't it get the value [m]NULL[/m] ?? (Wondering)
 

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