Thread: null pointers

Code:

class atom{
int protons;
int electrons;
int neutrons;
public:
atom* bond[4];
private:
friend int bind(atom&,atom&);
public:
 atom(int x) {
  protons=x;
  electrons=x;
  neutrons=x;
  for (int i=0;i<4;i++) bond[0]=NULL;
 }
 int type() { return protons; }
 int get_group() {
  int x=electrons;
  if (!x) return -1;
  if (x>=114) return -1;
  if (x==1) return 1;
  if (x==2) return 8; x-=2;
  for (int i=0;i<2;i++)   if (x<=8) return x;      x-=8;
  for (int i=0;i<2;i++) {
   if (x<=2) return x; x-=2;
   if (x<=10) return -2; x-=10;
   if (x<=6) return x+2; x-=6;
  }
  for (int i=0;i<2;i++) {
   if (x<=2) return x; x-=2;
   if (x<=14) return -2; x-=14;
   if (x<=10) return -2; x-=10;
   if (x<=6) return x+2; x-=6;
  }
  return -1;
 }

};
int bind(atom& x,atom& y) {
 int count=0; int count_1=0;
 if ((x.bond[3]!=NULL) || (y.bond[3]!=NULL)) return -1;
 while (x.bond[count++] != NULL);
 while (y.bond[count_1++]!=NULL);
 x.bond[count]=&y;
 y.bond[count_1]=&x;
}

int main()
{
 atom* atoms[5];
 atoms[0]=new atom(CARBON);
  for (int i=1;i<5;i++) {
   atoms[i]=new atom(HYDROGEN);
   bind (*atoms[0],*atoms[i]);
  }
  cout << "Protons: " << atoms[0]->type() << endl;
  cout << atoms[0]->bond[0]->type() << endl;
  cout << atoms[0]->bond[1]->type() << endl;
  cout << atoms[0]->bond[2]->type() << endl;
  cout << atoms[0]->bond[3]->type() << endl;
 return 0;
}

for some reason, when i try to print the types of the atoms that are bonded (the last 4 couts) it gives me an error. i'm almost certain the problem is because bond[0] is a NULL pointer. the bond[0] pointer should have been set by the bind function. can anyone spot the error?

I stopped at -

bond[0]=NULL;

should be

bond[i]=NULL;

This might be your problem.