Question 1

An empty contract named HelloWorld would look like this:

Accepted Answer

contract HelloWorld { }

Question 2

A bare-bones starting contract

Accepted Answer

pragma solidity >=0.5.0 <0.6.0; contract ContractName { 

}

Question 3

What is a contract?

Accepted Answer

A contract is the fundamental building block of Ethereum applications.

Question 4

All solidity source code should start with a ____________

Accepted Answer

version pragma

Question 5

Create an empty contract called ZombieFactory.

Accepted Answer

contract zombieFactory {}

Question 6

What are state variables

Accepted Answer

What are state variables

Question 7

State variable example

Accepted Answer

The uint data type is an unsigned integer, meaning its value must be non-negative.

Question 8

The following operations are the same as in most programming languages:

Accepted Answer

Addition: x + y

Subtraction: x - y,

Multiplication: x * y

Division: x / y

Modulus / remainder: x % y (for example, 13 % 5 is 3, because if you divide 5 into 13, 3 is the remainder)

Question 9

Example of an exponential operator in solidity

Accepted Answer

uint x = 5 ** 2; // equal to 5^2 = 25

Question 10

Create a uint named dnaModulus, and set it equal to 10 to the power of dnaDigits.

Accepted Answer

uint dnaModulus = 10 ** dnaDigits;

Question 11

Sometimes you need a more complex data type. For this, Solidity provides ________:

Accepted Answer

structs

Question 12

Example of struct

Accepted Answer

struct Person { 

uint age; 

string name; 

}

Question 13

Structs allow you to create more _________ data types that have ___________ properties.

Accepted Answer

complicated, multiple

Question 14

Create a struct named Zombie and let it have 2 properties: name (a string), and dna (a uint).

Accepted Answer

struct Zombie {

string name;

uint dna;

}

Question 15

When you want a collection of something, you can use an ______.

Accepted Answer

array

Question 16

There are two types of arrays in Solidity: ________ arrays and ______ arrays:

Accepted Answer

fixed, dynamic

Question 17

// Array with a fixed length of 2 elements:

Accepted Answer

uint[2] fixedArray;

Question 18

// another fixed Array, can contain 5 strings:

Accepted Answer

string[5] stringArray;

Question 19

// a dynamic Array - has no fixed size, can keep growing:

Accepted Answer

uint[] dynamicArray;

Question 20

Example of an array of structs.

Accepted Answer

Person[] people; // dynamic Array, we can keep adding to it

Question 21

You can declare an array as public, and Solidity will automatically create a getter method for it. The syntax looks like:

Accepted Answer

Person[] public people;

Question 22

Create a public array of Zombie structs, and name it zombies.

Accepted Answer

Zombie[] public zombies;

Question 23

A function declaration in solidity looks like the following:

Accepted Answer

function myFunction(string memory _name, uint _amount) public { }

Question 24

There are two ways in which you can pass an argument to a Solidity function:

Accepted Answer

By value and by reference

Question 25

What is required for all reference types such as arrays, structs, mappings, and strings?

Accepted Answer

It is required that variables should be stored- in memory

Question 26

Note: It's convention (but not required) to start function parameter variable names with an ____________ in order to differentiate them from global variables.

Accepted Answer

underscore (_)

Question 27

Create a public function named createZombie. It should take two parameters: _name (a string), and _dna (a uint). Don't forget to pass the first argument by value by using the memory keyword

Leave the body empty.

Accepted Answer

function createZombie (string memory _name, uint _dna) public {

}

Question 28

function createZombie (string memory _name, uint _dna) public {

// start here

}

In one line of code, fill in the function body so it creates a new Zombie, and adds it to the zombies array. The name and dna for the new Zombie should come from the

Accepted Answer

zombies.push(Zombie(_name, _dna));

Question 29

Example how to declare a private function:

Accepted Answer

uint[] numbers; 

function _addToArray(uint _number) private { 

numbers.push(_number); 

}

Question 30

it's convention to start private function names with an _____________.

Accepted Answer

underscore (_)

Question 31

function createZombie(string memory _name, uint _dna) public {

 zombies.push(Zombie(_name, _dna));

}

Our contract's createZombie function is currently public by default — this means anyone could call it and create a new Zombie in our contract! Le

Accepted Answer

function _createZombie(string memory _name, uint _dna) private {

 zombies.push(Zombie(_name, _dna));

}

Question 32

To return a value from a function, the declaration looks like this:

Accepted Answer

string greeting = "What's up dog"; 

function sayHello() public returns (string memory) {

 return greeting; 

}

Question 33

Solidity also contains _____ functions, which means you're not even accessing any data in the app.

Accepted Answer

pure

Question 34

Create a private function called _generateRandomDna. It will take one parameter named _str (a string), and return a uint. Don't forget to set the data location of the _str parameter to memory.

Mark it as view and allow the function body empty.

Accepted Answer

function _generateRandomDna(string memory _str) private view returns (uint) {

}

Cryptozombies

Creating a zombie factory

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