What does ! mean in Solidity?

Question

I'm studying Solidity and I couldn't understand what does [!] mean in ⑨⑫⑬.

What does it mean? And, how to use it?

Could you give any advice, please?

function sendReward(uint256 _reward, address _dest, uint256 _id) external 
  onlyOwner {
        require(!rewardSent[_id]); // ⑨
        require(_reward > 0); // ⑩
        require(address(this).balance >= _reward); // ⑪
        require(_dest != address(0)); // ⑫
        require(_dest != owner); // ⑬
        rewardSent[_id] = true; // ⑨
        _dest.transfer(_reward);
        emit RewardSent(_dest, _reward, _id);
    }

`!=` means "not equal" – Niklas Mertsch Mar 21 '19 at 13:31 — Niklas Mertsch, Mar 21 '19 at 13:31
And `!foo` means "not `foo`". – user94559 Mar 21 '19 at 17:08 — user94559, Mar 21 '19 at 17:08

score 2 · Accepted Answer · answered Mar 21 '19 at 13:33

2

According to the documentation != is the inequality operator. The following lines all evaluate to true:

1 == 1
1 != 2 
1 != 3

answered Mar 21 '19 at 13:33

Niklas Mertsch

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What does ! mean in Solidity?

1 Answers1