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contracts...events.sol

//SPDX-License-Identifier: MIT

pragma solidity ^0.8;

contract Events{

    //event is used to set the values on blockchain.
    event balance(address account,string message,uint val);

    //this function transaction function or simple function because its have no return did change any state variable
    function setBalance(uint _val) public{
        emit balance(msg.sender,"has value",_val);
    }
}

contract chatApp{
    //we can used the indexed keyword in event to indexed the transaction - used while DAPP development to arrang the transaction
    // Note- we can used indexed on three values - more than three gives an error
    //indexed used to arrange the values without forloop when you arrange the value
    //indexed is used for that
    event chatMessage(address indexed _from,address indexed _to,string _message);

    function sendMessage(address to_,string memory message_) public{
        emit chatMessage(msg.sender,to_,message_);
    }
}