Smart Contracts

This section covers writing a custom smart contract and deploying it on Harmony Testnet.

Writing our first Counter Smart Contract

In the contracts folder create a new file Counter.sol and add the following code block to it:

pragma solidity >=0.4.22 <0.8.0;
contract Counter {
uint256 private count = 0;
uint256 moneyStored = 0;
function incrementCounter() public {
count += 1;
function decrementCounter() public {
count -= 1;
function addMoney() payable public {
moneyStored += msg.value;
function getCount() public view returns (uint256) {
return count;
function getMoneyStored() public view returns (uint256){
return moneyStored;

In the migrations folder create another new file called 2_Counter.js and add the following code block:

const Migrations = artifacts.require("Counter");
module.exports = function (deployer) {

Checking the Solidity Smart Contract

truffle compile

If all was done correctly you should see something like this:

Compiling your contracts...
> Compiling ./contracts/Counter.sol
> Compiling ./contracts/Migrations.sol
> Compilation warnings encountered:
/home/rachit/Projects/demo/contracts/Counter.sol: Warning: SPDX license identifier not provided in source file. Before publishing, consider adding a comment containing "SPDX-License-Identifier: <SPDX-License>" to each source file. Use "SPDX-License-Identifier: UNLICENSED" for non-open-source code. Please see for more information.
> Artifacts written to /home/rachit/Projects/demo/build/contracts
> Compiled successfully using:
- solc: 0.7.0+commit.9e61f92b.Emscripten.clang


truffle migrate --network testnet --reset