Building Own Blockchain using C++

main.cpp

#include <iostream>
#include <string>
#include "SHA256.h"

using namespace std;

class block
{
    public :
    
    int index; //to store block number
    string timestamp; //to store date & time
    string data; // to staore data
    string previoushash; //to store hash of previous block
    string hash; //to store has of current block
    
    //Constructor - will be called automatically when object of block created
    block(int index, string timestamp, string data,string previoushash)
    {
        this->index = index;
        this->timestamp = timestamp;
        this->data = data;
        this->previoushash = previoushash;
        this->hash = calculateHash();
    
    }
    
    //function to calculate hash of given string using library pocosha2
    string calculateHash()
    {
        string source = to_string(index) + timestamp + data + previoushash;
        string hash;
        picosha2::hash256_hex_string(source, hash);
        return hash;
    }
    
};

class blockchain
{
    
public:
    vector <block> chain;
    blockchain() //Constructor
    {
        chain.push_back(createGenesisBlock());
    }
    block createGenesisBlock() //Function to create Genesis block
    {
        block b(0,"01/01/2018","Genesis Block","0");
        return b;
    }
    void addBlock(block b) //Method to add new block to blockchain
    {
        b.previoushash = getLatestBlock().hash;
        b.hash = b.calculateHash();
        chain.push_back(b);
    }
    block getLatestBlock() //Function to get last block from blockchain
    {
        return chain [this -> chain.size()-1];
    }
    
    string isChainValid() //validation of blockchain
    {
       for (int i=1; i< chain.size()- 1; i++)
       {
        block currentBlock = chain[i];
        block previousBlock = chain[i-1];
        if (currentBlock.hash != currentBlock.calculateHash())
        {
            return "Data on block is altered, so invalid blockchain";
        }
        if (currentBlock.previoushash != previousBlock.hash)
        {
            return "Data on block is altered, so invalid blockchain";
        }
       }
    return "No data tempered. This is valid blockchain";
    }
};


int main(int argc, const char * argv[]) {
    
    blockchain coin; //object of blockchain
    coin.addBlock(block(1,"02/01/2018","10 Coins","0")); //New block added
    coin.addBlock(block(2,"03/01/2018","20 Coins","0")); //New block added
    coin.addBlock(block(3,"04/01/2018","30 Coins","0")); //New block added
    
    //Uncomment following lines to check invalid blockchain use case
    //coin.chain[1].data = "1000 Coins";
    //coin.chain[1].hash = coin.chain[1].calculateHash();
    
    for (int i=0; i<=coin.chain.size()- 1; i++)
    {
        cout << "Index : " + to_string(coin.chain[i].index);
        cout << "\n";
        cout << "Timestamp : " + (coin.chain[i].timestamp);
        cout << "\n";
        cout << "Data : " + (coin.chain[i].data);
        cout << "\n";
        cout << "Previous Hash : " + (coin.chain[i].previoushash);
        cout << "\n";
        cout << "Hash : " + (coin.chain[i].hash);
        cout << "\n\n";
    }
    
    cout << coin.isChainValid();
    cout << "\n\n\n";
    return 0;
}