I recommend you to read the previous blog regarding the basics of Blockchain to understand this blog completely .
The Difference between Data Structures and Blockchain is that the assets are viable , which means that values in data structure can have double spending.
For Example : Ash has to give misty $100 and brock $100 , in data Structure . He can send both the same $100 , we can counter this by placing transactions in an order (Now the way that transactions are stored might be an issue ), and now check if he has the $ to do the transaction. Now the main issue here is order of transaction .
To Counter this issue , we use blockchain , as in blockchain during the mining process , double spending issue is taken care of .Now i am gonna execute steps to run a blockchain example on C++, this is a very raw program so if you provide suggestion’s , that would be great .
To look conceptually at Blockchain and Linked List have a lot of similarities , like the way there are linked , but Blockchain are immutable and use hashing (SHA_256) . Linked list is a data structure , you can read more about it on a previous blog.
There are in total 7 functions in this program ,
- Let’s look at our class’s , we have two class’s .One class represent the variables ,like amount , sender , receiver ,etc . Other class has function’s
class Node{
public:
int ammount;
string sender;
string receiver;
double id;
string timestamp;
string hash;
Node *next;
Node()//default constructor
{
ammount=0;
sender="Owner";
receiver="Fixed by Owner";
timestamp="NULL";
id=rand() % 100;//Unique id for each block
next=NULL;
}
Node(int n,string s, string r, string time )//constructor
{
ammount=n;
sender=s;
receiver =r;
// int t = stoi(time);
timestamp=time;
id=rand() % 100;//Unique id for each block
next=NULL;
}
};
class Blockchain : public Node
{
private:
Node *listptr,*temp;
//ptr is used to point at the current node and temp is used for temporary usages such as iterations , ammount storage for a small time.
public:
Blockchain()//
{
listptr=NULL;
temp=NULL;
//initializing the values to NULL , to avoid segmentation error
}
void Create(int , string, string);
void Display();
void HashDisplay();
int Isempty();
int len();
void Insert();
void Search();
void ProofofWork();
void Mining();
void Correctblock(Blockchain, Blockchain);
}lk1,lk2 ;
2. Now lets go into our Create function : We pass parameter’s to the function
void Blockchain :: Create(int num, string sender , string receiver)
{
time_t my_time = time(NULL);
timestamp=ctime(&my_time);
Node *newnode = new Node(num,sender,receiver,timestamp);
if(listptr == NULL)
listptr = temp = newnode;
else
{
temp -> next = newnode;//temp currently points towards current block
temp = temp->next;
}
}3. We now move on Display function :
void Blockchain:: Display()
{
Node * current_node = listptr ; /* temp points to first node*/
if ( Isempty()==0 )
{
cout<<"List is empty";
}
else
{
cout<<"\n";
while (current_node != NULL) //iterate till it reaches last block
{
cout <<"\n |\t"<< current_node->ammount <<" Sent to "<<current_node->receiver<<" by "<<current_node->sender<<" ,Transaction ID "<<current_node->id<<" ,at "<<current_node->timestamp<<" \t| "<< " ---> ";
current_node = current_node->next; /* move temp to the next node */
}
cout<< "NULL";
cout<<"\n";
}
}4.We now move onto Hash Display Function , We generally only work with hash value in blockchain , but for verification and simplicity , i had used normal display.
void Blockchain:: HashDisplay()
{
Node * current_node = listptr ; /* temp points to first node*/
if ( Isempty()==0 )
{
cout<<"List is empty";
}
else
{
std::hash<string> shashVal;
string final =current_node->sender+current_node->receiver;//hash value of Sender and receiver
std::hash<int> ihashVal;
int fin=current_node->id;//hash value of id
cout<<"\n";
while (current_node != NULL) //iterate till it reaches last block
{
cout <<"\n |\t"<< current_node->ammount <<" Hash value of transaction "<<shashVal(final)+ihashVal(fin)<< " ,at time "<<current_node->timestamp<<" \t| "<< " ---> ";
current_node = current_node->next; /* move temp to the next node */
}
cout<< "NULL";
cout<<"\n";
}
}
5.len function is used ahead , to find the longest blockchain to add our block in
int Blockchain ::len()
{
int count=0;
Node * current_node = listptr ; /* temp points to first node*/
if ( Isempty()==0 )
{
cout<<"List is empty";
}
else
{
while (current_node != NULL)
{
count+=1;
current_node = current_node->next; /* move temp to the next node */
}
}
return count;
}6.Search Function is Used to find a transaction in blockchain using transaction ID
void Blockchain :: Search()
{
int val;
cout<<"\n Enter ID to search in List \n";
cin>>val;
int find=0;
int count=0;
Node *current_node=listptr;
while (current_node->next!=NULL)
{
if (current_node->id==val)
{
find=1;
break;
}
count+=1;
current_node=current_node->next;
}
if(find ==1)
cout<<"\n Transaction is present at "<<count;
else
cout<<"\n Transaction not present";
}
7. Proof of work is done by checking some kind of pattern , in the blocks of a particular Blockchain , such as maybe in Blockchain A , the first two values of hash’s of each block are 00
//Assuming that there are two Blockchains , one starts with 1 while another one starts with zero assuming
Node * current_node = listptr ; /* temp points to first node*/
if ( Isempty()==0 )
{
cout<<"List is empty";
}
else
{
cout<<"\n";
while (current_node != NULL)
{
std::hash<string> shashVal;
string final =current_node->sender+current_node->receiver;
if (final[0]==1)
{
cout<<"Block A";
}
else if (final[1]==0)
{
cout<<"Block B";
}
else
cout<<"Block no pattern";
break;
}
}
}8.Mining this process is done by nodes in a blockchain , to verify transaction , this process takes care of Double spending issue , as once transaction is verified then only is it added on the blockchain
void Blockchain :: Mining()
{
/* Mining means transaction verification from the node server ,
Now this can't be done in Data Structures , This is the double spending problem
What the best way we can do in DS as of now is put it in an order
Assuming that two transactions happen from the same sender named ash ,
We put those two transactions in an order to check if he has balance to do these two transfer or not ,
most importantly that he is not sending the same money to both the receivers
Assuming that they both have 100 rupees right now in their accounts , So they can't make a transaction more than 100
*/
Node *current_node=listptr;
string senderMin;
cout<<"\n Enter Sender name to check \n";
cin>>senderMin;
int find=0;
int count=0;
while (current_node->next!=NULL)
{
if (current_node->sender==senderMin)
{
if(current_node->ammount <100 )
{
count+=1;
cout<<"Not enough credit , required credit: \t"<<current_node->ammount -100;
}
break;
}
current_node=current_node->next;
}
if (count==0)//If transactions is valid the
{
Node *newnode = new Node(current_node->ammount,current_node->sender,current_node->receiver,current_node->timestamp);
}
Correctblock(lk1,lk2);
}
9.Now when the transaction is verified , now the question is Which blockchain should we add the block to , the block is added to the longest Blockchain on the node , this is done by Correctblock function.
void Blockchain::Correctblock(Blockchain l1, Blockchain l2)
{
int x,y;
x=l1.len();
y=l2.len();
if(x>y)
{
cout<<"Blockchain A is longer hence , block will be added into ";
l1.Display() ;
}
else
{
cout<<"Blockchain B is longer hence , block will be added into ";
l2.Display();
}
}This is all i have been able to Understand from this topic , hopefully it was useful.
GitHub : https://github.com/kakabisht/Blockchain-implementation-without-networkingpart
Programmer Prodigy 