Create your first smart contract on the Ethereum Blockchain: Fundraising Contract

The first thing we need to do is define which version of solidity we will be using. Type this in at the top of the editor to define the version.

pragma solidity 0.5.6;

Our contract will be called “DappFrundraiser”. All of the code that exists in this contract must live within the two brackets. Also, include an empty constructor which we will use in the next block.

contract DappFundraiser 
}
						
					

So what exactly is our contract going to do?

Variables:
– owner : who is the contract admin (who deployed it)
– contributers: who has contributed to the fundraiser 
– contriubterAmount: the amount a user has contributed
– miniumContribution: the least amount somebody can contribute
– fundingGoal: how much funding does the contract need/want to raise

Functions:
– contribute() : contribute to the campaign
– getContributionBalance(): see how much funds have been added to the fundraiser from contributors

Now we can add our variables into the contract using the following syntax:

//  address of admin - the one who deployed the contract
address owner; 

// addresses of contributers
address[] public contributers;

// address of contributer - also allowing us to see how much was contributed
mapping(address => uint) public contributerAmount;
// minimum amount a user can contribute to the fundraiser
uint public minimumContribution;
//amount of funding needed before contract has reached its goal
uint public fundingGoal;

Solidity comes with a global variable called msg. We will use the following in this contract:
msg.sender (address): sender of the message (current call)
msg.value (uint): number of wei sent with the message

When deploying the contract, the constructor will be called one time, and one time only. This is the perfect opportunity to set the owner (admin), minimum contribution amount, as well as the funding goal for the contract.

pragma solidity 0.5.6;

contract DappFundraiser 
}

Now let’s create the function that allows us to check to contract Ehter balance. This is important because user funds should not be taken if the fundraising goal has already been met! This will act as a helper function in our contract.

function getContributionBalance() external view returns(uint) 

Ok now we are down to the last function before we deploy and test our first smart contract! The last but most import function “contribute()” is responsible for collecting the funds from users, while making sure this rule applies:
* The contribution payment must meet the minimum contribution fund we set in the constructor.

function contribute() external payable 
}

When we put it all together, your contract should look like this:

pragma solidity 0.5.6;

contract DappFundraiser 
function getContributionBalance() external view returns(uint) 
function contribute() external payable 
}
}

Now it is time to compile our smart contract and test it out. To do this, select the 0.5.6 compiler on the top right side and then click “compile”. If all goes as planned, you should see a green box on the middle of the screen on the right side with the contract name. See screenshot below: