Linked list problem.

Hi, I'm trying to do the last excercise of c++ beginner exercises.
I'm getting

Code:

Unhandled exception at 0x774a15de (ntdll.dll) in Graduation.exe: 0xC0000005: Access violation writing location 0x00000000.

I read a tutorial about linked lists and my understanding is that as far as you don't read/write beyond the last link, everything should be fine. Why does it do that?

Here is my code(void new_bunnies seems to be causing the problem). The exception doesn't occure at every excecution.

Code:

#include <iostream>
#include <time.h>
#include <string>




enum sex1{male, female, vampire};

std::string name1[]={"Acanthus","Ambrosia","Aria","Atiyana","Avalon","Azalea","Baylyn","Braelyn","Cadence","Calliope","Cashmere","Cassia",
"Cayenne","Chavonne","Fauna","Flint","Forest","Forsythia","Glimmer","Harmony","Jescha","Keveen","Lark","Lilac","Meadow","Osment",
"Quintessence","Rontae","Serendipity","Serenity","Slate","Sonnet","Taffeta","Temperance"};

std::string color[]={"white", "brown", "black", "spotted"};

struct bunny{
public:
    sex1 sex;
    std::string color;
    std::string name;
    int age;
    bool radioactive_mutant_vampire_bunny;
    int alive;             //false 0
    bunny* next;
    int number_of_bunny;
    };

bunny* root;
bunny* conductor; 
int n,r;
std::string female_color[700];
int k;
int mutant_count;

int number_of_bunnies=0;

void create_bunny();

void create_5_bunnies();

void up_age();

void new_bunnies();

void create_bunny();

void kill_old();




int main()
{
    srand(time(NULL));

    int bun=0;
    std::cout<<"male=0;female=1;vampire=2\n";

    create_5_bunnies();
    while(number_of_bunnies<1000){

    std::cout<<"NEW_BUNNIES";
    new_bunnies();
    std::cout<<"UP_AGE";
    up_age();
    std::cout<<"\nKILL_OLD\n";
    kill_old();

    std::cout<<number_of_bunnies<<" bunnies\n";

    if(number_of_bunnies==0){
        std::cout<<"All bunnies died";
        number_of_bunnies=1000;
        bun=1;
    }

    }
    
    if(bun!=1){std::cout<<"Bunny population exceeded 1000";}
    std::cin.get();
    return(0);
}

void create_5_bunnies(){
    root=new bunny;
    conductor=root;

    for(n=1;n<(5+1);n++){
        number_of_bunnies++;

        r=rand()%2+1;
        if(r==1)conductor->sex=male;
        else if(r==2)conductor->sex=female;

        r=rand()%4+1;
        if(r==1)conductor->color="white";
        else if(r==2)conductor->color="brown";
        else if(r==3)conductor->color="black";
        else if(r==4)conductor->color="spotted";

        r=rand()%34+0;
        conductor->name=name1[r];

        conductor->age=0;

        r=rand()%100+1;
        if(r==1||r==2){
            conductor->radioactive_mutant_vampire_bunny=true;
            conductor->sex=vampire;
        }
        else{conductor->radioactive_mutant_vampire_bunny=false;}

        
        std::cout<<"Bunny "<<conductor->name<<" was born!"<<conductor->sex<<"\n";

        conductor->alive=1;

        conductor->next=new bunny;
        conductor=conductor->next;
        conductor->next=0;
    }
    }

void up_age(){
    conductor=root;
    while(conductor!=NULL){
        conductor->age++;
        conductor=conductor->next;
    }
}

void new_bunnies(){
    int female_count=0;
    bool male_count=false;
    int bunnies_to_create=0;
    int bunnies_created=0;
    k=1;
    conductor=root;
    
    while(conductor!=NULL){  
        if(conductor->sex==female&&conductor->alive==1){female_count=female_count+1;
        female_color[k]=conductor->color;
        k++;
        female_color[k]=conductor->color;
        k++;
        }
        else if(conductor->sex==male){male_count=true;}
        conductor=conductor->next;
    }
    std::cout<<female_count<<" female bunnys.";
    bunnies_to_create=(female_count*2);
    std::cout<<bunnies_to_create<<" bunnies should born\n";
    if(bunnies_to_create>0){
        conductor=root;
        k=1;
        while(bunnies_created!=bunnies_to_create){
        if(conductor->alive==0){
            std::cout<<"creating bunny2\n";
            create_bunny();
            k++;
            if(conductor->next!=0){conductor=conductor->next;}
        }
        else if(conductor->next==0&&bunnies_created!=bunnies_to_create){
            std::cout<<"creating bunny3\n";
            create_bunny();
            bunnies_created++;
            k++;
            conductor->next=new bunny;
            conductor=conductor->next;
            conductor->next=0;
            }
        else{conductor=conductor->next;}
        }
    }
    conductor=root;
}

void create_bunny(){
        r=rand()%2+1;
        if(r==1)conductor->sex=male;
        else if(r==2)conductor->sex=female;

        conductor->color=female_color[k];

        
        r=rand()%34+0;
        conductor->name=name1[r];

        conductor->age=0;

        r=rand()%100+1;
        if(r==1||r==2){
            conductor->radioactive_mutant_vampire_bunny=true;
            conductor->sex=vampire;
        }
        else{conductor->radioactive_mutant_vampire_bunny=false;}

        number_of_bunnies++;
        
        std::cout<<"Bunny "<<conductor->name<<" was born!"<<conductor->sex<<"\n";

        conductor->alive=1;
}

void kill_old(){
    conductor=root;
    while(conductor!=NULL){
        if(conductor->age>10){
        conductor->alive=0;
        number_of_bunnies--;
        std::cout<<conductor->name<<" died!";}
        conductor=conductor->next;
    
    }
}

Here is the snippet of code where visual studio points me after the exception.

Code:

size_type max_size() const
        {    // return maximum possible length of sequence
        size_type _Num = this->_Alval.max_size();
        return (_Num <= 1 ? 1 : _Num - 1);
        }

line 2 is what you should focus at first.What is _Alval?
The exception doesn't occure at every excecution by chance(if no exception,this means that by chance you read only valid memory)

Originally Posted by std10093

line 2 is what you should focus at first.What is _Alval?
The exception doesn't occure at every excecution by chance(if no exception,this means that by chance you read only valid memory)

Sorry for the mess, I didn't post the actual code whats causing the problem(edited the first post), the second code is the exception that visual studio shows me(figured it might help).

But the real question is, what is causing the exception in my code(the 1st one)? I now know that it doesn't happen by chance, but I don't know, what triggers it.

You should normally only call the "srand" function once per program.
You should call it before the first call to the "rand" function.

No idea if that is the cause of your program error; but, it might be the cause.

Tim S.

Originally Posted by stahta01

You should normally only call the "srand" function once per program.
You should call it before the first call to the "rand" function.

No idea if that is the cause of your program error; but, it might be the cause.

Tim S.

I'll try it out.
Edit: Didn't work (edited the code in the first post). Kinda forgot that you only have to seed once, thank you for reminding it.

The problem seems to be between the lines 140 and 149. I just don't know what exactly

You are doing this step twice; either do it only once or double the size of the array.

Note: I would increase the array female_color to at least the max number of rabbits.

Tim S.

Code:

        female_color[k]=conductor->color;
        k++;
        female_color[k]=conductor->color;
        k++;

Originally Posted by stahta01

You are doing this step twice; either do it only once or double the size of the array.

Note: I would increase the array female_color to at least the max number of rabbits.

Tim S.

Code:

        female_color[k]=conductor->color;
        k++;
        female_color[k]=conductor->color;
        k++;

Wow, increasing the array worked, you're amazing!(doing the step twice was intentional)Wasn't about the linked lists after all....
Thx for the quick replies.

Now, I've got another problem which I didn't want to add in the beginning, since I was stuck on the new_bunnies function.
This time, it's the make_mutant_bunnies function(starting at line 221).

My purpose is to start from the beginning of the links and search the first link which has a mutant variable value 0 and change mutant state, to be mutant(1). It does change mutant variable of 1 bunny, however, it seems to be deleting some info, since the new_bunnies is called, it says female_count is 0, why is that?

EDIT: now I get

Unhandled exception at 0x774a15de (ntdll.dll) in Graduation.exe: 0xC0000005: Access violation writing location 0x00000050.

Code:

#include <iostream>
#include <time.h>
#include <string>




enum sex1{male, female, vampire};

std::string name1[]={"Acanthus","Ambrosia","Aria","Atiyana","Avalon","Azalea","Baylyn","Braelyn","Cadence","Calliope","Cashmere","Cassia",
"Cayenne","Chavonne","Fauna","Flint","Forest","Forsythia","Glimmer","Harmony","Jescha","Keveen","Lark","Lilac","Meadow","Osment",
"Quintessence","Rontae","Serendipity","Serenity","Slate","Sonnet","Taffeta","Temperance"};

std::string color[]={"white", "brown", "black", "spotted"};

struct bunny{
public:
    sex1 sex;
    std::string color;
    std::string name;
    int age;
    int radioactive_mutant_vampire_bunny;
    int alive;             //false 0
    bunny* next;
    int number_of_bunny;
    };

bunny* root;
bunny* conductor; 
int n,r;
std::string female_color[1000];
int k;
int mutant_count;

int number_of_bunnies=0;

void create_bunny();

void create_5_bunnies();

void up_age();

void new_bunnies();

void create_bunny();

void kill_old();

void make_mutant_bunnies();




int main()
{
    srand(time(NULL));

    int bun=0;
    std::cout<<"male=0;female=1;vampire=2\n";

    create_5_bunnies();
    while(number_of_bunnies<1000){

    std::cout<<"NEW_BUNNIES";
    new_bunnies();
    std::cout<<"UP_AGE";
    up_age();
    std::cout<<"\nKILL_OLD\n";
    kill_old();
    std::cout<<"\nMAKING MUTANTS\n";
    make_mutant_bunnies();

    std::cout<<number_of_bunnies<<" bunnies\n";

    if(number_of_bunnies==0){
        std::cout<<"All bunnies died";
        number_of_bunnies=1000;
        bun=1;
    }

    }
    
    if(bun!=1){std::cout<<"Bunny population exceeded 1000";}
    std::cin.get();
    return(0);
}

void create_5_bunnies(){
    root=new bunny;
    conductor=root;

    for(n=1;n<(5+1);n++){
        number_of_bunnies++;

        r=rand()%2+1;
        if(r==1)conductor->sex=male;
        else if(r==2)conductor->sex=female;

        r=rand()%4+1;
        if(r==1)conductor->color="white";
        else if(r==2)conductor->color="brown";
        else if(r==3)conductor->color="black";
        else if(r==4)conductor->color="spotted";

        r=rand()%34+0;
        conductor->name=name1[r];

        conductor->age=0;

        r=rand()%100+1;
        if(r==1||r==2){
            conductor->radioactive_mutant_vampire_bunny=1;
            conductor->sex=vampire;
        }
        else{conductor->radioactive_mutant_vampire_bunny=0;}

        
        std::cout<<"Bunny "<<conductor->name<<" was born!"<<conductor->sex<<"\n";

        conductor->alive=1;

        conductor->next=new bunny;
        conductor=conductor->next;
        conductor->next=0;
    }
    }

void up_age(){
    conductor=root;
    while(conductor!=NULL){
        conductor->age++;
        conductor=conductor->next;
    }
}

void new_bunnies(){
    int female_count=0;
    bool male_count=false;
    int bunnies_to_create=0;
    int bunnies_created=0;
    k=1;
    conductor=root;
    
    while(conductor!=NULL){  
        if(conductor->sex==female&&conductor->alive==1){female_count=female_count+1;
        female_color[k]=conductor->color;
        k++;
        female_color[k]=conductor->color;
        k++;
        }
        else if(conductor->sex==male){male_count=true;}
        conductor=conductor->next;
    }
    std::cout<<female_count<<" female bunnys.";
    bunnies_to_create=(female_count*2);
    std::cout<<bunnies_to_create<<" bunnies should born\n";
    if(bunnies_to_create>0){
        conductor=root;
        k=1;
        while(bunnies_created!=bunnies_to_create){
        if(conductor->alive==0){
            std::cout<<"creating bunny2\n";
            create_bunny();
            k++;
            if(conductor->next!=0){conductor=conductor->next;}
        }
        else if(conductor->next==0&&bunnies_created!=bunnies_to_create){
            std::cout<<"creating bunny3\n";
            create_bunny();
            bunnies_created++;
            k++;
            conductor->next=new bunny;
            conductor=conductor->next;
            conductor->next=0;
            }
        else{conductor=conductor->next;}
        }
    }
    conductor=root;
}

void create_bunny(){
        r=rand()%2+1;
        if(r==1)conductor->sex=male;
        else if(r==2)conductor->sex=female;

        conductor->color=female_color[k];

        
        r=rand()%34+0;
        conductor->name=name1[r];

        conductor->age=0;

        r=rand()%100+1;
        if(r==1||r==2){
            conductor->radioactive_mutant_vampire_bunny=1;
            conductor->sex=vampire;
        }
        else{conductor->radioactive_mutant_vampire_bunny=0;}

        number_of_bunnies++;
        
        std::cout<<"Bunny "<<conductor->name<<" was born!"<<conductor->sex<<"\n";

        conductor->alive=1;
}

void kill_old(){
    conductor=root;
    while(conductor!=NULL){
        if(conductor->age>10){
        conductor->alive=0;
        number_of_bunnies--;
        std::cout<<conductor->name<<" died!";}
        conductor=conductor->next;
    
    }
}

void make_mutant_bunnies(){
    
    int mutant_created=0;
    mutant_count=0;
    conductor=root;
    while(conductor!=NULL){              
        if(conductor->radioactive_mutant_vampire_bunny==1){
            mutant_count=mutant_count+1;
        }
    conductor=conductor->next;
    }

    conductor=root;

    while(mutant_created!=mutant_count){                                      //ERROR HERE
        if(conductor->next=0){
            std::cout<<"ALL VAMPIRES";
            system("PAUSE");
        }

            std::cout<<"Checking for vampires:";

            if(conductor->radioactive_mutant_vampire_bunny==0){
            conductor->radioactive_mutant_vampire_bunny=1;
            std::cout<<"Bunnie "<<conductor->name<<" just got vampired!";
            conductor->sex=vampire;
            mutant_created++;
            }

        conductor=conductor->next;
    }

}

line 236 are you sure that conductor->next is not NULL?

Edit:
Here is the situation in my opinion:
At line 250 you set conductor to NULL.Then the loop continues,and we go to line 236 and ask for conductor->next,while the conductor itself is NULL .

Here is the way i followed to trace that(your code with some cout for me)

Code:

cout<<"edw1"<<endl;
    while(mutant_created!=mutant_count){     cout<<"edw12"<<endl;  
    if(conductor==NULL)cout<<"yes"<<endl; else cout<<"not"<<endl;//ERROR HERE
        if(conductor->next=0){
            std::cout<<"ALL VAMPIRES";cout<<"edw13"<<endl;  
            system("PAUSE");cout<<"edw14"<<endl;  
        }
 cout<<"edw15"<<endl;  
            std::cout<<"Checking for vampires:";
 cout<<"edw16"<<endl;  
            if(conductor->radioactive_mutant_vampire_bunny==0){cout<<"edw17"<<endl;  
            conductor->radioactive_mutant_vampire_bunny=1;cout<<"edw18"<<endl;  
            std::cout<<"Bunnie "<<conductor->name<<" just got vampired!";
            conductor->sex=vampire;cout<<"edw19"<<endl;  
            mutant_count++;
            }
 cout<<"edw20"<<endl;  
 if(conductor->next==NULL)cout<<"yes"<<endl; else cout<<"not"<<endl;
        conductor=conductor->next;cout<<"edw21"<<endl;  
    }

also some tips:
you may write "using namespace std" at the top of the file
e.g.

Code:

#include <iostream>
#include <time.h>
#include <string>

using namespace std;
 
enum sex1{male, female, vampire};

However if you are in a .h file try not to use this tip,because then you force the person who included this .h file use this namespace too.

tip No.2 Do not use system("PAUSE");

Wait, I think I know what the problem is:
Vampires can be male or female!

Have you learnt about asserts? They are great tools for documenting and checking conditions that should be true. For example if a certain pointer variable is not supposed to be null at a certain point, then you assert that by saying:

Code:

assert(someVariable != NULL);

Then if a bug has caused it to be NULL by mistake at that point, then the program will break into the debugger and show you the line with the assertion failure.

Originally Posted by std10093

line 236 are you sure that conductor->next is not NULL?

Edit:
Here is the situation in my opinion:
At line 250 you set conductor to NULL.Then the loop continues,and we go to line 236 and ask for conductor->next,while the conductor itself is NULL .

My idea was that it begins from the first link, and then picks the first link which isn't vampire. If it reaches the end, it means that it didn't found any link which isn't a vampire and that means all the bunnies are vampires.
Now, what I can't understand is, why does it go to the end of the list with a single

Code:

conductor=conductor->next

line(250), shouldn't it just go to the second link, since at line 233 I made conductor to be the first link(root)?

I probably should make line 236.... and now I just looked at it.

Code:

if(conductor->next=0)

It doesn't ask if conductor is NULL, it makes the conductor to be null.

Code:

if(conductor->next==0)

is correct. And I probably should make it if(conductor==0) as you said.
Edit: Also changed mutant_count++ to mutant_created++ since it would'nt end the loop.
Edit2: Thank you for the tips. I used the system("PAUSE") right now to make it quick, have a workaround for it. Happen to know any multi-platform alternatives? Mine is windows only. As for the namespace, I've been told that it's may cause some problems if another person is going to work with your code, so I'm not using it and making it a good habit.

Originally Posted by iMalc

Wait, I think I know what the problem is:
Vampires can be male or female!
Have you learnt about asserts? They are great tools for documenting and checking conditions that should be true. For example if a certain pointer variable is not supposed to be null at a certain point, then you assert that by saying:

Code:

assert(someVariable != NULL);

Then if a bug has caused it to be NULL by mistake at that point, then the program will break into the debugger and show you the line with the assertion failure.

I have not learned about asserts, they seem to be pretty useful. Thanks.
But vampires cannot be female or male, sex has 3 options, male, female, or vampire and I changed the sex value

Code:

conductor->sex=vampire

Line 14 in the last std10093's post.

Originally Posted by Vana Papi

I probably should make line 236.... and now I just looked at it.

Code:

if(conductor->next=0)

It doesn't ask if conductor is NULL, it makes the conductor to be null.

Code:

if(conductor->next==0)

is correct. And I probably should make it if(conductor==0) as you said.

Oh,good observation!Bravo!!!

Originally Posted by Vana Papi

Edit: Also changed mutant_count++ to mutant_created++ since it would'nt end the loop.

Infinite loops.Always be aware of them.

Originally Posted by Vana Papi

Edit2: Thank you for the tips. I used the system("PAUSE") right now to make it quick, have a workaround for it. Happen to know any multi-platform alternatives? Mine is windows only.

If it is for your usage only,and want something quick,try cin.Declare an int at this point of file where you want your program to stall for you.The program will be stalled as long as you wish,until you input something.
e.g.

Code:

...
int t;
cin>>t;
...

Execution will not continue until you input something.

Another solution is the sleep function.
e.g.

Code:

#include <windows.h>//header needed
...
sleep(5)
..

Your program will stall for 5 secs.

Originally Posted by Vana Papi

As for the namespace, I've been told that it's may cause some problems if another person is going to work with your code, so I'm not using it and making it a good habit.

Try to avoid it at .h files.In .cpp files there is no problem using it ,and it is very helpful

Originally Posted by Vana Papi

I have not learned about asserts, they seem to be pretty useful. Thanks.
But vampires cannot be female or male, sex has 3 options, male, female, or vampire and I changed the sex value

Code:

conductor->sex=vampire

Line 14 in the last std10093's post.

asserts are a tool for debuging.It is not necessary to learn it now if you are a beginner

Originally Posted by std10093

Another solution is the sleep function.
e.g.

Code:

#include <windows.h>//header needed
...
sleep(5)
..

Your program will stall for 5 secs.

That is not correct.
It's Sleep with a capital S and it takes milliseconds as its argument, so it will stall 5 milliseconds.
But you may as well go ahead and read SourceForge.net: Pause console - cpwiki

Originally Posted by Elysia

That is not correct.
It's Sleep with a capital S and it takes milliseconds as its argument, so it will stall 5 milliseconds.
But you may as well go ahead and read SourceForge.net: Pause console - cpwiki

Elysia is correct.Sorry for that:/