Calculator.sol

pragma solidity ^0.5.11;

contract Calculadora {
    // Variables
    uint256 public res;
    uint256 limit; // Limit será el máximo entero que puede representar la calculadora
    
    // Constructor
    constructor() public {
        res = 0;
        limit = 115792089237316195423570985008687907853269984665640564039457584007913129639935;
    }
    
    // Metodos
		// function function_name([args]) [visibility] [mutability] [returns([type])] [modifiers] {}
        
		// Suma
        function add(uint256 toSum) public returns(uint256) {
            require(res + toSum != limit, "Overflow!!");
            res += toSum;
            return res;
        }
        
        // Resta
        function substract(uint256 toSubstract) public returns(uint256) {
            require(res - toSubstract != limit, "Overflow!!");
            res -= toSubstract;
            return res;
        }
        
        // Multiplicación
        function multiply(uint256 toMultiply) public returns(uint256){
            require(res * toMultiply != limit, "Overflow!!");
            res *= toMultiply;
            return res;
        }
        
        // División
        function division(uint256 toDivide) public returns(uint256){
            require(res / toDivide != limit, "Overflow!!");
            res /= toDivide;
            return res;
        }
        
        // Reset
        function reset() public {
            res = 0;
        }
}