Doing a exercise about bunny colony, hit a wall - c++

Question

I was doing last exercise from this list (its called graduation): http://www.cplusplus.com/forum/articles/12974/ but had one major problem. The code I wrote runs, but it will crash at so time (after deleting half bunnies), sometimes after program deletes half bunnies first time, sometimes after 10 such cycles, note that i havent implemented alot yet because i want to fix this bug, with your help of course. Also I know this is not code review, but some small tips about style and improving would be good too. So this is code i wrote so far:
Main.cpp:
include bunnyList.h
include windows.h
using namespace std;
int main(){
srand(time(NULL));
bunnyList Colony;
int turns = 0;
Colony.setUp();
while(Colony.getColonySize() > 0){
//New turn
Colony.increaseAgeAndKill();
Colony.breedBunnies();
std::cout << "Turn: "<< turns << ". Colony size: " << Colony.getColonySize() << std::endl;
//Get rid of these food eaters
if(Colony.getColonySize() > 1000){
std::cout << "500 bunnies died!" << std::endl;
Colony.killHalfBunnies();
}
Sleep(100);
turns++;;
}
}
bunnyList.h:
#ifndef BUNNYLIST_H
#define BUNNYLIST_H
#include <stdlib.h>
#include "node.h"
#include <time.h>
#include <iostream>
#include <string>
const int numOfNames = 4;
const int numOfColors = 4;
const int bunniesIni = 5;
const std::string colors[numOfColors] = {"Black", "White", "Brown", "Spotted"};
const std::string maleNames[numOfNames] = {"Joe", "Rafael", "Buby", "Messi"};
const std::string femaleNames[numOfNames] = {"Reichel", "Agnesa", "Mr Flufy", "Flower"};
class bunnyList{
private:
node *head;
int noOfBunnies;
node *current, *prev;
public:
bunnyList();
void newBunny(std::string);
void killHalfBunnies();
void increaseAgeAndKill();
void deleteNode();
void breedBunnies();
void setUp();
int getRandomNumber(int) const;
std::string getRandomColor();
std::string getRandomName(bool);
bool isMaleRandom();
int getColonySize() const;
};
#endif
bunnyList.cpp:
#include "bunnyList.h"
bunnyList::bunnyList(){
noOfBunnies = 0;
}
void bunnyList::setUp(){
std::string temp = "";
head = NULL;
for(int i = 0; i <= bunniesIni; i++){
newBunny(temp);
}
}
void bunnyList::killHalfBunnies(){
prev = head;
current = head;
while(noOfBunnies > 500){
if(getRandomNumber(2) == 1){
deleteNode();
continue;
} else if(current == NULL){
current = head;
prev = head;
} else {
prev = current;
current = current->next;
continue;
}
}
}
void bunnyList::newBunny(std::string color){
node *bunny = new node();
node *temp = head;
if(color == ""){
bunny->color = getRandomColor();
} else {
bunny->color = color;
}
bunny->isMale = isMaleRandom();
bunny->name = getRandomName(bunny->isMale);
bunny->age = 0;
bunny->next = NULL;
bunny->isBreedable = 0;
if(head == NULL){
head = bunny;
return;
}
while(temp->next != NULL){
temp = temp->next;
}
temp->next = bunny;
noOfBunnies++;
}
void bunnyList::increaseAgeAndKill(){
current = head;
prev = head;
while(current != NULL){
current->age++;
//Check if bunny can breed
if(current->age > 2){
current->isBreedable = 1;
}
//Check if its time to die :/
if(current->age > 10){
deleteNode();
}
prev = current;
current = current->next;
}
current = head;
prev = head;
}
void bunnyList::breedBunnies(){
node *temp = head;
bool oneMale = 0;
int femaleCount = 0;
//Check if there is at least one breedable male
while(temp!=NULL){
if(temp->isMale && temp->isBreedable){
oneMale = 1;
break;
}
temp = temp->next;
}
//For every female bunny over 2 years old a new bunny is born
temp = head;
if(oneMale){
while(temp != NULL){
if(temp->isMale == 0 && temp->isBreedable){
newBunny(temp->color);
}
temp = temp->next;
}
}
}
void bunnyList::deleteNode(){
if(current==head){
head = current->next;
prev = head;
delete current;
current = head;
noOfBunnies--;
} else if(current->next==NULL){
delete current;
prev->next = NULL;
prev = head;
current = head;
noOfBunnies--;
} else {
prev->next = current->next;
current->next = NULL;
delete current;
current = prev->next;
noOfBunnies--;
}
}
std::string bunnyList::getRandomName(bool isMale){
int r = getRandomNumber(numOfNames - 1);
if(isMale)
return maleNames[r];
return femaleNames[r];
}
std::string bunnyList::getRandomColor(){
int r = getRandomNumber(numOfColors - 1);
return colors[r];
}
bool bunnyList::isMaleRandom(){
if(getRandomNumber(2) == 1) {return true;}
return false;
}
int bunnyList::getRandomNumber(int limit) const{
return rand() % limit + 1;
}
int bunnyList::getColonySize() const{
return noOfBunnies;
}
node.h:
#ifndef NODE_H_INCLUDED
#define NODE_H_INCLUDED
#include <string>
class node {
friend class bunnyList;
private:
std::string name;
int age;
std::string color;
bool isMale;
node *next;
bool isBreedable;
public:
};
#endif // NODE_H_INCLUDED
Thank you for your help.

Answer 1

Since you asked for the review...
NEVER write using namespace std. Never. Just this morning there was a problem asked on SO where the reason for the issue at hand was that notorious line. I wonder who and why suggested that this is a good approach - there should be a book somewhere with this. If I had my way, it's author would be condemned to eternal manual removal of this line from every file.
Even without reading a line from the code, just by explanations alone, I know that the problem is most likely (100% likely, as in) to be related to memory management. You are freeing the memory which was not allocated properly, you are freeing the same memory twice or you are freeing something which was not allocated at all or you are accessing the memory after it was freed. Look at your deletes and check them.
On the style. Your code basically is an implementation of the business logic-aware list. Generally, this is not a good practice. It is much better to implement a generic list, supporting addition, deletion and other generic list operations, and than implement your business logic on top of this generic list.
Do not use current in your list. Instead, pass a node to be deleted in your delete function.
Lastly, run your program in the debugger and look into the variables you are deleting.
EDIT
Answering questions in commments.
Here is what I meant by business logic separation. There is a generic data structure, called list. It can be a list of anything, bunnies or space rockets, doesn't matter - but it still supports the basic list operations. Obviously, the two most important are insert and delete, but it is not the only operations for generic list. You can read wikipedia on list (data structure) for general ideas and look into std::list as in implementation. Now, you have your specific use case for list, a list of bunnies. For that specific use case you will add functionality on top of generic list. To clarify further, deleting an item from the list is something generic list supports. But 'killing a rabit' when the poor creature ages 10 years is something of the business logic. It contains iterating over list of rabbits (provided by generic list), checking age and making a decision to eliminate the creature (business-logic level) and than deleting the element (generic list). If this code were to be written using std::list, it would like approximately following:
std::list<Bunny> bunnies;
for (auto bunny = bunnies.cbegin(), end = bunnies.cend(); bunny != end; ++bunny) {
if (bunny->age() > 10)
bunny = bunnies.erase(bunny);
}

Answer 2

I got a crash too. It crashed in deleteNode, trying to reference current->next when current was NULL.
This was called from bunnyList::killHalfBunnies, in this code, which is the problem I find:
if (getRandomNumber(2) == 1){
deleteNode();
continue;
}
else if (current == NULL){
current = head;
prev = head;
}
The problem is you call deleteNode, which assumes that current is not NULL, before checking that current is in fact not NULL. I rearranged the if's as shown here, and I'm no longer getting a crash:
if (current == NULL)
{
current = head;
prev = head;
}
else if (getRandomNumber(2) == 1)
{
deleteNode();
continue;
}
It would also be wise to put a check inside deleteNode, so that if it is called when current is NULL, it can handle it. Possibly by throwing an exception or otherwise warning you.
Since you also asked about style: comments in deleteNode (and elsewhere) would make it all clearer!
I assume this is a class assignment, and that's why you're not using std::list.