basic solidity calculator

Calculator-Empty.sol

// SPDX-License-Identifier: MIT
pragma solidity 0.8.13;

contract Calculator {
    int c;

    // 1. create a constructor function that initializes our base calculator value
    constructor() {}

    // 2. create interface functions for adding, subtracting, multiplying, and dividing c by a number a
    //    add keywords and parameters if needed.
    function add() {}
    function sub() {}
    function mul() {}
    function div() {}
    
    // 3. create a function for setting c back to 0
    function reset() {}

    // 4. create a getter function to return the current state of the calculator value c
    function getResult() {}
}

Calculator.sol

// SPDX-License-Identifier: MIT
pragma solidity 0.8.13;

contract Calculator {
    int c;

    constructor() {
        c = 0;
    }

    function add(int a) public {
        c = c + a;
    }

    function sub(int a) public {
        c = c - a;
    }

    function mul(int a) public {
        c = c * a;
    }

    function div(int a) public {
        require(a > 0, "The second parameter should be larger than 0");

        c = c / a;
    }

    function reset() public {
        c = 0;
    }

    function getResult() public view returns (int x) {
        return c;
    }
}