Difference between ( ) and [ ]

[zchuanru]

Hi All,

I am new here. I have a question about when to use ( ) and [ ]

Example of code below:

//// SPDX-License-Identifier: MIT

pragma solidity ^0.6.0;

contract SimpleStorage {
    struct person {
        string personName;
        uint256 personNum;
    }

    person [] public getPerson ;
    mapping (string=>uint256) public personToNum;

    function storePerson (string memory _storePersonName, uint256 _storePersonNum) public {
       getPerson.push (person(_storePersonName, _storePersonNum));
       personToNum[_storePersonName] = _storePersonNum;
    }
}

For this line:
personToNum[_storePersonName] = _storePersonNum;

Why is it using [ ] and not ( )?

Many thanks.

[cromewar]

Hello @solarwhale
Each language has it's own conventions for using some symbols., but they are common conventions so...
() is usually used to refer to function calls,
[] is usually used to refer to numeric/contextual index on data types like arrays.

with this context...

set on this index -> personToNum[_storePersonName]= _storePersonNum; <- this value.

I hope this info might help.

[zchuanru]

Thank you!

But why doesn't the following line need [ ]?

getPerson.push (person(_storePersonName, _storePersonNum));

In the above line, is it storing data into the getPerson array and hence does not need [ ]?

Does it mean that only when I want to call data from an array, I will need [ ]?

[cromewar]

This is because push is a function and as a function it is you pass the parameter inside the () , also person is not an array is a struct so person also uses () for the parameters.
Cheers.

[zchuanru]

I see!

Thanks so much!