Created using remix-ide: Realtime Ethereum Contract Compiler and Runtime. Load this file by pasting this gists URL or ID at https://remix.ethereum.org/#version=soljson-v0.5.13+commit.5b0b510c.js&optimize=false&runs=200&gist=

contracts...EventExample.sol

pragma solidity ^0.5.11;

contract EventExample {
    
    mapping(address => uint) public tokenBalance;
    
    event TokensSent(address _from, address _to, uint _amount);
    
    constructor() public {
        tokenBalance[msg.sender] = 100;
    }
    
    function sendToken(address _to, uint _amount) public returns(bool) {
        require(tokenBalance[msg.sender] >= _amount, "You don't have enough token");
        
        assert(tokenBalance[_to] + _amount >= tokenBalance[_to]);
        assert(tokenBalance[msg.sender] - _amount <= tokenBalance[msg.sender]);
        
        tokenBalance[msg.sender] -= _amount;
        tokenBalance[_to] += _amount;
        
        emit TokensSent(msg.sender, _to, _amount);
        
        return true;
    }
}