BCDV 1010 : Lab - 3

  1. Create a simple GBCToken contract that consists of -

    • map of balanceOf to store balances of the token

    • constructor to initialise the balance of contract creator with maximum number of token (total supply)

    • transfer function to transfer the token from the sender to someone.

      • It should be public so that everyone can use this function to send token to each other.

      • It should check whether the sender has enough tokens before transferring.

      • It should check for overflows before transferring.

      • It should emit a Transfer event

Test the contract on Remix, make sure constructor, balanceOf and transfer() are functional.

Solution

 1
 2
 3
 4
 5
 6
 7
 8
 9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
// SPDX-License-Identifier: MIT
pragma solidity ^0.7.0;


import "https://github.com/OpenZeppelin/openzeppelin-contracts/blob/master/contracts/math/SafeMath.sol";

contract GBCToken {

    using SafeMath for uint;

    mapping (address => uint) balanceOf;

    event Transfer(address indexed _from,address indexed _to,uint indexed _amount);

    constructor(){
        balanceOf[msg.sender] = 5000;
    }

    function transfer(address _receiver, uint _amount) public returns(bool _sufficient){
        require(balanceOf[msg.sender] >= _amount, "Insufficient balance");
        balanceOf[msg.sender] = balanceOf[msg.sender] - _amount;
        balanceOf[_receiver] = balanceOf[_receiver] + _amount;
        emit Transfer(msg.sender, _receiver,_amount);
        _sufficient = true;
    }
}