What it does

This smart contract code uses the Ethereum Blockchain to issue lottery tickets to paying customers, who then have a random chance of winning everyone else's bets for themselves.

How I built it

I used the Ethereum solidity Remix IDE.

Challenges I ran into

Integrating the contract into a browser, as I was not skilled with Javascript.

Accomplishments that I'm proud of

I managed to learn to read and use an Ethereum contract in a matter of days.

What I learned

There is more to a Decentralized app than just the contract, some javascript will be necessary to build a full UI.

The Code

pragma solidity ^0.4.11;

contract Lotto {

    mapping(address => uint) internal players_wager;
    mapping(uint => address) internal players;
    uint internal num_of_users = 0;
    uint public total_wagers = 0;

    address internal owner;
    string public game_name;
    uint internal rand;
    uint public winning_number;

    function Lotto() {
        owner = msg.sender;
        game_name = "Ethereum Lotto";

    function wager() public payable  {
        if (msg.value > 0) {
            if (players_wager[msg.sender] == 0) {
                players[num_of_users] = msg.sender;
                num_of_users += 1;
            players_wager[msg.sender] += msg.value;
            total_wagers += 1;

    function wager_ether_value(address addr) returns(uint){
        return players_wager[addr];

    function user_address(uint nb) returns(address){
        return players[nb];

    function test_random() returns(uint) {
        rand = uint(block.blockhash(block.number-1)) % total_wagers;
        return rand;

    function decide_winner() public returns(uint) {
        if (msg.sender == owner) {
            uint sum = 0;
            winning_number = uint(block.blockhash(block.number-1)) % total_wagers;
            for (uint i=0; i < num_of_users; i++) {
                sum += players_wager[players[i]];
                if (sum >= winning_number) {


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