Rusty with c++ need some help with errors involving pointers and stuff

Bit rusty with C++ and not sure how to fix these errors i'm getting. Any help is much appreciated!!!

Here's the errors:

DFS.cpp: In function 'void DFS(Node*)':
DFS.cpp:64: error: cannot convert 'Node' to 'Node*' for argument '1' to 'void DFS_Visit(Node*)'
DFS.cpp: In function 'Node* makeGraph()':
DFS.cpp:130: error: no match for 'operator*' in '**(((Node*)(((long unsigned int)i) * 16ul)) + graph)'
DFS.cpp: In function 'Node* makeSample()':
DFS.cpp:150: error: no match for 'operator=' in '*(((Node*)(((long unsigned int)i) * 16ul)) + graph) = 0l'
DFS.cpp:15: note: candidates are: Node& Node:: operator=(const Node&)
DFS.cpp:158: error: name lookup of 'i' changed for new ISO 'for' scoping
DFS.cpp:148: error: using obsolete binding at 'i'



And here's the code:

Code:

---

#include <iostream>
#include <iomanip>
#include <cstdlib>

using namespace std;


int operationsCounter=0;
int ntime=0, verts, edges;
string* color = new string[1];
int* pi = new int[1];
int* d = new int[1];
int* f = new int[1];

struct Node{
  int data;
  Node* next;
};
void InsertAfter(Node *head, int value){
  if(head==NULL){
    Node* temp=NULL;
    temp = new Node;
    temp->data = value;
    temp->next = NULL;
    head = temp;
  }else{
    Node *temp = new Node;
    temp->data = value;
    temp->next = (head)->next;
    (head)->next = temp;
  }
}


void DFS_Visit(Node* u)
{
  color[u->data]="gray";
  d[u->data]=(++ntime);
  int v=u->data;
  while((u=u->next)!=NULL)
  {
    if (color[u->data]=="white")
    {
      pi[u->data]=v;
      DFS_Visit(u);
    }
  }
  color[v]="black";
  f[v]=(++ntime);
}

void DFS(Node* G)
{
  for (int u=0; u<verts; u++)
  {
    color[u]="white";
    pi[u]=-1;
  }
  ntime=0;
  for (int u=0; u<verts; u++)
  {
    if (color[u]=="white")
    {
      DFS_Visit(G[u]);
    }
  }
}

void printResults()
{
  cout << "      d    f    pi " << endl;
  for (int i=0; i<verts; i++)
  {
    if(i<10)
      cout << "    " << i;
    else if(i<100)
      cout << "  " << i;
    else if(i<1000)
      cout << "  " << i;
    else
      cout << " " << i;
    if(d[i]<10)
      cout << "    " << d[i];
    else if(d[i]<100)
      cout << "  " << d[i];
    else if(d[i]<1000)
      cout << "  " << d[i];
    else
      cout << " " << d[i];
    if(f[i]<10)
      cout << "    " << f[i];
    else if(f[i]<100)
      cout << "  " << f[i];
    else if(f[i]<1000)
      cout << "  " << f[i];
    else
      cout << " " << f[i];
    if(pi[i]<10)
      cout << "    " << pi[i] << endl;
    else if(pi[i]<100)
      cout << "  " << pi[i] << endl;
    else if(pi[i]<1000)
      cout << "  " << pi[i] << endl;
    else
      cout << " " << pi[i] << endl;
   
  }
  cout << endl << endl;
  cout << "Number of operation: " << operationsCounter << endl;
}

bool alreadyInList(Node* llist, int data)
{
  if(llist==NULL)
    return false;
  else if(data==llist->data)
    return true;
  else
    return alreadyInList(llist->next, data);
}

Node* makeGraph()
{
  int u, v;
  u=0;
  v=0;
  Node* graph = new Node[5];
  for(int i=0; i<5; i++)
  {
    &graph[i]=NULL;
    InsertAfter(&graph[i], i);
  }
  for(int i=0; i<edges; i++)
  {
    while(alreadyInList(&graph[u], v))
    {
      u = rand() % verts;
      v = rand() % verts;
    }
    InsertAfter(&graph[u], v);
  }
  return graph;
}

Node* makeSample()
{
  Node* graph = new Node[5];
  for(int i=0; i<verts; i++)
  {
    graph[i]=NULL;
    InsertAfter(&graph[i], i);
  }
  InsertAfter(&graph[0], 1);
  InsertAfter(&graph[1], 2);
  InsertAfter(&graph[1], 3);
  InsertAfter(&graph[2], 3);
  InsertAfter(&graph[2], 4);
  InsertAfter(&graph[4], i);
  return graph;
}

int main()
{
  int option;
  while (option!=3)
  {
    cout << "Please select an option: " << endl;
    cout << "1) Run DFS on the sample graph" << endl;
    cout << "2) Run DFS on a customized random graph" << endl;
    cout << "3) Exit" << endl;
    cin >> option;
    if(option==1)
    {
      verts=5;
      edges=6;
          color = new string[verts];
      pi = new int[verts];
      d = new int[verts];
      f = new int[verts];
      operationsCounter=0;
      DFS(makeSample());
      printResults();
    }
    if(option==2)
    {
      cout << "How many vertices would you like the graph to have?" << endl;
      cin >> verts;
      cout << "How many edges would you like the graph to have?" << endl;
      cin >> edges;
          color = new string[verts];
      pi = new int[verts];
      d = new int[verts];
      f = new int[verts];
      operationsCounter=0;
      DFS(makeGraph());
      printResults();
    }
  }
  cout << "Thank you.  Goodbye!";
  return 0;
}

---

For

Quote:

---

DFS.cpp: In function 'void DFS(Node*)':
DFS.cpp:64: error: cannot convert 'Node' to 'Node*' for argument '1' to 'void DFS_Visit(Node*)'

---

change

Code:

---

DFS_Visit(G[u]);

---

to:

Code:

---

DFS_Visit( &G[u] );

---

For

Quote:

---

DFS.cpp:150: error: no match for 'operator=' in '*(((Node*)(((long unsigned int)i) * 16ul)) + graph) = 0l'
DFS.cpp:15: note: candidates are: Node& Node:: operator=(const Node&)

---

try changing

Code:

---

graph[i]=NULL;

---

to:

Code:

---

&graph[i]=NULL;

---

For

Quote:

---

DFS.cpp:158: error: name lookup of 'i' changed for new ISO 'for' scoping
DFS.cpp:148: error: using obsolete binding at 'i'

---

Move the int i = 0; out before the for loop in:

Code:

---

for(int i=0; i<verts; i++)

---

Ah thanks! But

Code:

---

&graph[i]=NULL;

---

still gives the error:

Quote:

---

DFS.cpp: In function 'Node* makeGraph()':
DFS.cpp:130: error: invalid lvalue in assignment

---

I do not think you can assign NULL to the address of an object. What you can do is assign NULL to a pointer. But graph is a pointer, not an array of pointers. Consequently, I think you want to make graph a dynamic array of pointers instead. Either that, or you are trying to zero each node, but that would have already been done for you.

Yes, I want it to be an array of pointers (Nodes)..... How do I do that then?

How did the OP post this syntax highlighted C++ code?
Is it automatically enabled now, i think i need to post some code to test it! :)

Quote:

---

Yes, I want it to be an array of pointers (Nodes)..... How do I do that then?

---

You could write:

Code:

---

Node** graph = new Node*[5];

---

However, there are more problems:

• Why do you use global variables in your code?
• Why do you give your variables such undescriptive names as pi, d and f?
• Where is your delete[] to match your new[]?
• Where is your delete to match your new?
• In main, why do you use option before it is initialised?

http://dwks.theprogrammingsite.com/myprogs/cfonline.htm

u->data is causing a seg fault...... why?

in particular the first time i think it is used is in (where i know it is causing the seg fault)

color[u->data]="gray";

in DFS_Visit

any thoughts?

Code:

---

template <typename Unknown>
class Shahrukh : public FilmStar {

    int i;
    float f;

public:
    void dance();
    void act();
    long double earn();
};

---

Have you fixed the problems I listed? If so, post your updated code. If not, fix them.

Quote:

---

Originally Posted by laserlight

You could write:

• Why do you use global variables in your code?
• Why do you give your variables such undescriptive names as pi, d and f?
• Where is your delete[] to match your new[]?
• Where is your delete to match your new?
• In main, why do you use option before it is initialised?

---

-multiple functions modifying them, so only way I know
-hw assignment and thats what they said to use, lol, its for an algorithms class so they know what they are supposed to be (pi=parent, d=discovered time, f=finished time)
-don't have one.... don't really need it
-just initialized it to 0 to begin with

i have extra couts in there to find the seg fault so you can just ignore them....

Code:

---

#include <iostream>
#include <iomanip>
#include <cstdlib>

using namespace std;


int operationsCounter=0;
int ntime=0, verts, edges;
string* color = new string[1];
int* pi = new int[1];
int* d = new int[1];
int* f = new int[1];

struct Node{
  int data;
  Node* next;
};
void InsertAfter(Node *head, int value){
  if(head==NULL){
    Node* temp=NULL;
    temp = new Node;
    temp->data = value;
    temp->next = NULL;
    head = temp;
  }else{
    Node *temp = new Node;
    temp->data = value;
    temp->next = (head)->next;
    (head)->next = temp;
  }
}


void DFS_Visit(Node* u)
{
        cout << "---in DFS_Visit u=" << endl;
        cout << "---" << &u->data << endl;
  color[u->data]="gray";
  cout << "---color" << endl;
  d[u->data]=(++ntime);
  cout << "---d" << endl;
  int v=u->data;
  cout << "---DFS_Visit before while" << endl;
  while((u=u->next)!=NULL)
  {
          cout << "---DFS_Visit in while u=" << u->data << endl;
    if (color[u->data]=="white")
    {
      pi[u->data]=v;
      DFS_Visit(u);
    }
  }
  cout << "---DFS_Visit after while" << endl;
  color[v]="black";
  f[v]=(++ntime);
}

void DFS(Node** G)
{
  for (int u=0; u<verts; u++)
  {
    color[u]="white";
    pi[u]=-1;
  }
  ntime=0;
  cout << "---DFS 1" << endl;
  for (int u=0; u<verts; u++)
  {
    if (color[u]=="white")
    {
      DFS_Visit(G[u]);
    }
  }
  cout << "---DFS 2 done" << endl;
}

void printResults()
{
  cout << "      d    f    pi " << endl;
  for (int i=0; i<verts; i++)
  {
    if(i<10)
      cout << "    " << i;
    else if(i<100)
      cout << "  " << i;
    else if(i<1000)
      cout << "  " << i;
    else
      cout << " " << i;
    if(d[i]<10)
      cout << "    " << d[i];
    else if(d[i]<100)
      cout << "  " << d[i];
    else if(d[i]<1000)
      cout << "  " << d[i];
    else
      cout << " " << d[i];
    if(f[i]<10)
      cout << "    " << f[i];
    else if(f[i]<100)
      cout << "  " << f[i];
    else if(f[i]<1000)
      cout << "  " << f[i];
    else
      cout << " " << f[i];
    if(pi[i]<10)
      cout << "    " << pi[i] << endl;
    else if(pi[i]<100)
      cout << "  " << pi[i] << endl;
    else if(pi[i]<1000)
      cout << "  " << pi[i] << endl;
    else
      cout << " " << pi[i] << endl;
   
  }
  cout << endl << endl;
  cout << "Number of operation: " << operationsCounter << endl;
}

bool alreadyInList(Node* llist, int data)
{
        cout << "---already in list" << endl;
  if(llist==NULL)
    return false;
  else if(data==llist->data)
    return true;
  else
    return alreadyInList(llist->next, data);
}

Node** makeGraph()
{
  int u, v;
  u=0;
  v=0;
  Node** graph = new Node*[5];
  for(int i=0; i<5; i++)
  {
    graph[i]=NULL;
    InsertAfter(graph[i], i);
  }
  for(int i=0; i<edges; i++)
  {
    while(alreadyInList(graph[u], v))
    {
      u = rand() &#37; verts;
      v = rand() % verts;
    }
    InsertAfter(graph[u], v);
  }
  return graph;
}

Node** makeSample()
{
  Node** graph = new Node*[5];
  int i=0;
  while(i<verts)
  {
    graph[i]=NULL;
    InsertAfter(graph[i], i);
        i++;
  }
  InsertAfter(graph[0], 1);
  InsertAfter(graph[1], 2);
  InsertAfter(graph[1], 3);
  InsertAfter(graph[2], 3);
  InsertAfter(graph[2], 4);
  InsertAfter(graph[4], i);
  cout << "---Sample graph made ..........es." << endl;
  return graph;
}

int main()
{
  int option=0;
  while (option!=3)
  {
    cout << "Please select an option: " << endl;
    cout << "1) Run DFS on the sample graph" << endl;
    cout << "2) Run DFS on a customized random graph" << endl;
    cout << "3) Exit" << endl;
    cin >> option;
    if(option==1)
    {
      verts=5;
      edges=6;
          color = new string[verts];
      pi = new int[verts];
      d = new int[verts];
      f = new int[verts];
      operationsCounter=0;
      DFS(makeSample());
      printResults();
    }
    if(option==2)
    {
      cout << "How many vertices would you like the graph to have?" << endl;
      cin >> verts;
      cout << "How many edges would you like the graph to have?" << endl;
      cin >> edges;
          color = new string[verts];
      pi = new int[verts];
      d = new int[verts];
      f = new int[verts];
      operationsCounter=0;
      DFS(makeGraph());
      printResults();
    }
  }
  cout << "Thank you.  Goodbye!";
  return 0;
}

---

Quote:

---

-multiple functions modifying them, so only way I know

---

You obviously know another way ;) Pass them to the functions as arguments. There is yet another way, which I think manav is hinting at: they may be better off as member variables of a class.

Quote:

---

-hw assignment and thats what they said to use, lol, its for an algorithms class so they know what they are supposed to be (pi=parent, d=discovered time, f=finished time)

---

Your lecturer is entitled to use abbreviations in class to fit everything in the lecture slides. You have no such privilege since your code can span much more than lecture slides reasonably can, thus you should give appropriate names to your variables. Names like parent, discovered_time and finished_time certainly are not too long, and yet are descriptive enough.

Quote:

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-don't have one.... don't really need it

---

You do need to match your new[] with delete[] and your new with delete unless you want memory leaks.

Quote:

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-just initialized it to 0 to begin with

---

Your code says otherwise.

- thats just ugly and more work than required and since its now almost 2 a.m. and i'm running on 2 hours of sleep definately feeling lazy :-P
- actually the assignment description says to call them that.... sure i doubt i'd lose points if i did use something else, but i've also got this algorithm memorized with pi, d, and f so works for me
-doesn't matter for this class...
-int option=0;
while (option!=3)
nope looks initialized before use to me :-P

but as for the seg fault.... what wrong with color[u->data]="gray";

Quote:

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- thats just ugly and more work than required and since its now almost 2 a.m. and i'm running on 2 hours of sleep definately feeling lazy :-P

---

As you wish. I will not be helping you until you fix that. Global variables make your code more difficult to trace.

Quote:

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- actually the assignment description says to call them that.... sure i doubt i'd lose points if i did use something else, but i've also got this algorithm memorized with pi, d, and f so works for me

---

Okay, in that case you should at least provide comments to state their proper names.

Quote:

---

-doesn't matter for this class...

---

As you wish. I will not be helping you until you fix that. Your lecturer chose C++ instead of Java, so write your C++ code like C++, not Java.

Quote:

---

-int option=0;
while (option!=3)
nope looks initialized before use to me :-P

---

In your updated code, yes. That's good.

It is quite simple: if you want help, do things correctly when asked to do so. If not, then as you have admitted, you are lazy and do not deserve help.

EDIT:
In fact, I suspect that the use of global variables is indirectly related to your current problem. You are simply having difficulty tracing the code yourself.

well thats pretty cruel..... thanks for the help you did give me

guess i'll hope someone else is willing to figure out why color[u->data]="gray"; is causing a seg fault, or i'll seek help elsewhere

for now i desperately need sleep

For now, you desperately need to fix your problems. If you don't, you will not learn. This is C++, not Java. Welcome to C++.

Quote:

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well thats pretty cruel.....

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Not really. If I were to start helping you any further, the first thing I would do is fix those problems so I can understand your code more easily.

Quote:

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thanks for the help you did give me

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You're welcome.

Quote:

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for now i desperately need sleep

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Yeah, rest is usually a good idea if you need it :)

Quote:

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Originally Posted by JJJIrish05

guess i'll hope someone else is willing to figure out why color[u->data]="gray"; is causing a seg fault

---

What compiler are you using? Do you know how to use an interactive debugger? My guess is that you are either accessing color out of bounds (what is the value of u->data?), or u is NULL or points to some random address.

added the deletes to fix that stuff.....

&u->data prints out 0 and u->data seg faults.... why?

I'm using gcc on a linux machine to compile, never used a debugger

Quote:

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Originally Posted by JJJIrish05

&u->data prints out 0 and u->data seg faults.... why?

---

Because u doesn't point to anything, it is 0. 0->data is what is causing your seg fault.

Quote:

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I'm using gcc on a linux machine to compile, never used a debugger

---

You should learn how to use gdb, the Gnu debugger.

I won't testify as to which debugger is the best, but I prefer Visual Studio. Easy to setup, easy to get used to.
No need to remember command lines or search for an appropriate gui for it.

If you require a graphical debugger under *nix, you can also use ddd, or Code::Blocks, which is cross-platform.