output_ptr Assertion Error in Main - Cairo-lang

Why does this Cairo program put powers of 2 in the memory?

What does it mean to declare a 'local' variable inside a 'let'?

Checking result of an L1 -> L2 message/invoke in Starknet

when to use tail call optimization in a cairo smartcontract

What is the inefficiency in this cairo code using alloc_locals

Why does range_check_ptr chek for [0, 2^128) instead of [0, P/2)

Testing Starknet Cairo contract function with address

How to generate a proof for a Cairo program and verify it?

Where can I find a list of decorators available in Cairo?

How to disable error squiggles for Cairo Compiler in VS Code

How do I develop against cairo devnet with browser wallets?

Does Cairo support int256, or negative numbers in general? 

How can i learn Cairo with Python base?

Cairo: How to reassign Uint256 in a conditional

Cairo: Difference between amount and gas_fee

Cairo Error: 'While expanding the reference 'test_struct' in'

Changing a variable with an initialized value recursively with if statements

How expensive are bitwise operations (and/or/xor) vs arithmetic in Cairo?

How to calculate the sum of the digits of a felt in Cairo?

Cairo: How do I write a custom error message when an assert fails?

Cairo Error: Getting Expected expression of type 'felt', got '__main__.getCurrNumber.Return'

Cairo error for Unexpected '.' after ... which is future

Cairo Error: Getting Expected expression of type 'felt', got '(res : felt)'

Did not have to pay gas fee when calling same function multiple times in Starknet?

Cairo: Javascript API for cairo compile

How many Cairo steps does it take to compute one Pedersen hash?

Cairo: How would I store negative numbers then retrieve them as negatives?

How to write "and" conditional logic in Cairo?

How do I write a log based 2 function in Cairo?

Cairo error: Accessing struct/tuple members for r-value structs is not supported yet

Cairo error: Unknown identifier 'bitwise_ptr' when using keccak

Cairo 0.10.0 Error: Cannot unpack return value error

Cairo: How to return true from a function?

How large can addresses be in Cairo?

Cairo: Getting function selector

Cairo: How do I iterate through an array of structs?

Cairo: Unknown value for memory cell at address

Cairo: Getting the zero address

Cairo: Expected '__main__.Id' to be a struct. Found: 'future'

Cairo Error: Unexpected token Token('LPAR', '('). Expected: identifier.

Writing a "not" operation in Cairo

Cairo: Iterating through arrays

How do you check if a number is even in Cairo?

Cairo Error calling function: Expected 'function_name' to be a struct. Found: 'function'.

Namespaces in Cairo

Cairo: How do I find the current contract's address?

Declaring Strings in Cairo

Implicit Arguments in Cairo

Does cairo have payable functions?

What does ret do in Cairo?

Cairo: When do you use tempvar and when do you use local

Getting the CLASS_HASH of a contract in Cairo

Cairo: How do write a log function in Cairo

Cairo: Using less than or greater than in conditional

Cairo: Cannot unpack multiplication error

开始学习Cairo

Cairo: What is the difference between let and tempvar?

Expect function call to fail in cairo?

Cairo: are builtins always needed to be expressed in function signature?

Cairo: Cannot unpack error

Cairo: Else if statement

Cairo: How do I initialize an array in cairo

Cairo: Getting the squared summation of felts in an array

Cairo error "Expected expression of type 'starkware.cairo.common.uint256.Uint256' to have an address."

Immutable Memory in Cairo

Cairo start.

How to import uint256 in Cairo?

Cairo Passing Functions

Cairo v. Solidity

Cairo Error: 'range_check_ptr' cannot be used as an implicit return value. Consider using a 'with' statement.

Cairo Array Item Removal

Searching for Cairo Questions

Cairo Automatic Events

Cairo Owner Only Fuctions

Infinite Recursion Error on Cairo Compile

Cairo Multiple Storage Vars

test another new question new

Creating Elements via a function

List of Cairo Decorators

Cairo: Where/how is it defined and why is it much smaller than the field prime?

How to calculate the minimum decimal number that can store 20 chars long string as a field element?

How to fix `bud_ptr`

hardhat test

Any idea what this could be caused by?

signing a message using account.signMessage(data) | starknet.js

Another vanilla Cairo question, what are the sorts of references

Hey, is there anyway to debug Cairo contracts in hardhat environment? Something like hardhat console in solidity

a pointer with a hint, without doing a memory allocation

Is it possible to import local python files into hints?

Does writing it to zero actually do something?

Which is this extension that shows you errors before compilation ser?

 Is there a way to accelerate pytest for cairo contract?

A plan to get better visibility when a transaction got received but not placed into a block?

Abi.encode and Abi.decode in Cairo?

Cairo OR operator

Cairo: let vs tempvar what is the difference?

anyone know how to disconnect the connected wallet on the frontend with starknetjs or another way?

Does anyone know a vim plugin for StarkNet smart contracts?

Can you help how to change the code so that it outputs 400 as well?

```
// The following code outputs the numbers 100, 200, 300.
// 1. Click on "Run" to see the output.
// 2. Change it to output 400 as well.

// Use the output builtin.
%builtins output

// Import the serialize_word() function.
from starkware.cairo.common.serialize import serialize_word

func main{output_ptr: felt*}() {
// Output 100 by calling serialize_word.
serialize_word(100);
// Output 200.
serialize_word(200);
// Output 300.
serialize_word(300);
// Return.
return ();
}
```

---

> Answers to this question are a part of the ✨ **17 days of Cairo Lang with Playground & Newton.** ✨ 

*Vote for your favorite answer - the best answer will win a $10 award. A new day – a new reward! During the next 17 days, our goal is to attract more developers to the Cairo language and to systematize the knowledge of Cairo lang. [Read rules](https://www.notion.so/17-days-of-Cairo-Lang-with-Playground-Newton-550dfcda6a2d449ca468be293c776578)*

Newton

How to make output like "hello world" in Cairo Language (StarkNet)?

1. Can anyone explain how to get Goerli ETH tokens?

2. Also want to know how to bridge tokens from the Goerli ETH testnet and move them to Goerli2 (StarkNet)?


---

> thank's for your answers, summing up how to transfer funds and how to use Faucet on Ethereum:


1. For receiving ETH on Goerli Test Net, I used [Goerli PoW Faucet](https://goerli-faucet.pk910.de/).
As an alternative, [https://goerlifaucet.com/](https://goerlifaucet.com/) can be used, but it is required to authorize.

2. I installed ArgentX using the links below and transferred funds using the [HashStack service for StarkNet](https://goerli2-bridge.hashstack.finance)

![https://www.bbntimes.com/images/Ethereum_Faucet.jpeg](https://www.bbntimes.com/images/Ethereum_Faucet.jpeg)

vargastartup

StarkNet Faucet: How can I get a Goerli-2 eth faucet tokens (StarkNet)?


Hello! This is day 16 of the 17 days of the Cairo Challenge. In this exercise it is required to submit your first StarkNet contract. When you try to make it, you get an error:

```solidity
Error: code:20:1: Unsupported %lang directive. Are you using the correct compiler?
%lang starknet
^************^
```

Can you show your solution to [playground](https://www.cairo-lang.org/playground/) exercise “StarkNet contract” and also send a link to your contract, and a screenshot where you use your `add` method?

```solidity
// [StarkNet](https://starkware.co/product/starknet/) is a permissionless decentralized ZK-Rollup operating
// as an L2 network over Ethereum, where any dApp can achieve
// unlimited scale for its computation, without compromising
// Ethereum's composability and security.
//
// This is a simple StarkNet contract.
// Note that you won't be able to use the playground to compile and run it,
// but you can deploy it on the [StarkNet Planets Alpha network](https://medium.com/starkware/starknet-planets-alpha-on-ropsten-e7494929cb95)!
//
// 1. Click on "Deploy" to deploy the contract.
//    For more information on how to write Cairo contracts see the
//    ["Hello StarkNet" tutorial](https://cairo-lang.org/docs/hello_starknet).
// 2. Click on the contract address in the output pane to open
//    [Voyager](https://goerli.voyager.online/) - the StarkNet block explorer.
// 3. Wait for the page to load the information
//    (it may take a few minutes until a block is created).
// 4. In the "STATE" tab, you can call the "add()" transaction.

// The "%lang" directive declares this code as a StarkNet contract.
%lang starknet

@view
func add(x: felt, y: felt) -> (res: felt) {
    return (res=x + y);
}
```

---

> Answers to this question are a part of the ✨ 17 days of Cairo Lang with Playground & Newton. ✨
> 

*Vote for your favorite answer - the best answer will win a $10 award. A new day – a new reward! During the next 17 days, our goal is to attract more developers to the Cairo language and to systematize the knowledge of Cairo lang. [Read rules](https://www.notion.so/17-days-of-Cairo-Lang-with-Newton-550dfcda6a2d449ca468be293c776578)*

How to submit a StarkNet contract?

Hello! This is Day 2 of the 17 days of the Cairo challenge. And I have no idea how to solve the [playground](https://www.cairo-lang.org/playground/) exercise “Functions”. Perhaps you can help me?

```python
// The following code is missing the function `add1`.
// 1. Click on "Run" to see the error.
// 2. Write the function `add1`, based on `add1_square`, so
//    that the program terminates successfully.
//
// Note that `add1` doesn't have to call other functions.
//
// You can learn more about functions [here](https://www.cairo-lang.org/docs/how_cairo_works/functions.html).

// Write your code here.

func add1_square(x: felt) -> (x: felt) {
    // Call `add1` and unpack the result into `z`.
    let (z) = add1(y=x);
    return (x=z * z);
}

func main() {
    // Call `add1_square` and save the result into `res`.
    let (res) = add1_square(x=12);

    // Verify the computation.
    assert res = (12 + 1) * (12 + 1);
    return ();
}
```

---
> Answers to this question are a part of the ✨ **17 days of Cairo Lang with Playground & Newton.** ✨ 

*Vote for your favorite answer - the best answer will win a $10 award. A new day – a new reward! During the next 17 days, our goal is to attract more developers to the Cairo language and to systematize the knowledge of Cairo lang. [Read rules](https://www.notion.so/17-days-of-Cairo-Lang-with-Newton-550dfcda6a2d449ca468be293c776578)*

How to write a function in Cairo Lang (StarkNet)?

Can someone explain the difference `between unsigned_div_rem` and `uint256_unsigned_div_rem`?

Why unit version process so many extra steps, but overall number of steps for computing are different for these methods?



Can someone explain the difference between unsigned_div_rem and uint256_unsigned_div_rem?

following this page from the docs https://starknet.io/docs/hello_starknet/intro.html
I copied the code, compiled it using starknet compile, and when I go to declare it using starknet declare Im getting 
Status code: 500; text: {"code": "StarknetErrorCode.ENTRY_POINT_NOT_FOUND_IN_CONTRACT", "message": "Entry point <address>caed693fa4008dcdb4963b3 not found in contract with class hash <address>975148f6af3e9abddfdc701."}
Any help would be appreciated.

_This question was originally posted on [StarkNet Discord](https://www.newton.so/view?tags=discord)_

StarknetErrorCode.ENTRY_POINT_NOT_FOUND_IN_CONTRACT error in Cairo. Can anyone help?

Hey! I hope I'm at the right channel 🙂 I had a ques about contract creation gas fees. are there none? I can deploy to goreli starkent w/o any fees but couldnt find any doc

_This question was originally posted on [StarkNet Discord](https://www.newton.so/view?tags=discord)_

What are gas fees in StarkNet?

Hello guys, i was wondering what are the projects on starknet that plan to do the domain .stark  plz

I know there is starknet id, but is there any others ?

_This question was originally posted on [StarkNet Discord](https://www.newton.so/view?tags=discord)_

What are the projects on starknet that plan to do the domain .stark?


Hey, I want to concatenate two arrays with known sizes in Cairo lang.
Is there any simple way how to do it? Can you share some of your code?

Is there any simple way to concat two arrays with known sizes in Cairo?

Hey this message looks very confusing.
`GatewayError: {'contract_address': ['Expected hex string, got: "0x01C438231cD70f47d1acB8404E51734c1Fb4d79AC55813b3E861fB1EF78Da0D6".']}`

Any hints on this?

_This question was originally posted on [StarkNet Discord](https://www.newton.so/view?tags=discord)_

CairoLang error: `GatewayError: {'contract_address': ['Expected hex string, got: 

>Hello! This is day 5 of the 17 days of the Cairo Challenge. And I have no idea how to solve the [playground](https://www.cairo-lang.org/playground/) exercise “Revoked references”. Can you run these 6 steps and write down what you see?

```
// The scope of some types of references in Cairo (e.g., return values of
// functions and temporary variables) is somewhat restricted.
// For example, a call to another function may revoke those references.
//
// 1. Try to run the following code. You should get an error that `x` was revoked
//    (this is because of the second call to `foo`).
// 2. In simple cases, like this one, the compiler can solve this automatically
//    if the "alloc_locals" keyword is used within the function's scope.
//    Add "alloc_locals;" to the beginning of main(), and make sure the code works.
// 3. To understand what happens behind the scenes, replace "alloc_locals;" with
//    "ap += SIZEOF_LOCALS;" - this command allocates memory cells for local variables
//    (you'll need them below) but doesn't enable the mechanism that
//    automatically resolves revoked references.
//    Trying to run the code now should result in the original error.
// 4. Solve the problem manually by copying the value of `x` to a local variable
//    (e.g., "local x2 = x;"). Local variables are not revoked when functions
//    are called.
//    You can read more about local variables [here](https://www.cairo-lang.org/docs/how_cairo_works/consts.html#local-vars).
// 5. You can even use the same name: "local x = x;".
//    This is called "reference rebinding", where the meaning of `x` changes:
//      Before this line, `x` refers to the return value.
//      After that, `x` refers to the local variable.
// 6. A shorter syntax is "let (local x) = foo(10);" which achieves the same goal.
//    Try it!

%builtins output

from starkware.cairo.common.serialize import serialize_word

// Returns a^3 for a != 0 and 1 otherwise.
func foo(a) -> (res: felt) {
    if (a == 0) {
        return (res=1);
    } else {
        return (res=a * a * a);
    }
}

// Outputs the value 10^3 + 5^3.
func main{output_ptr: felt*}() {
    let (x) = foo(10);
    let (y) = foo(5);
    serialize_word(x + y);
    return ();
}
```

---

> Answers to this question are a part of the ✨ 17 days of Cairo Lang with Playground & Newton. ✨
> 

*Vote for your favorite answer - the best answer will win a $10 award. A new day – a new reward! During the next 17 days, our goal is to attract more developers to the Cairo language and to systematize the knowledge of Cairo lang. [Read rules](https://www.notion.so/17-days-of-Cairo-Lang-with-Newton-550dfcda6a2d449ca468be293c776578)*



Cairo Lang / StarkNet: What are Revoked references? What is alloc_locals?

Hi all! I wanted to know if anyone knows by chance if the Starknet Name Service is working or not?

_This question was originally posted on [StarkNet Discord](https://www.newton.so/view?tags=discord)_

Is the Starknet Name Service working or not?

Hey how can I get ETH for the test net in StarkNet?

_This question was originally posted on [StarkNet Discord](https://www.newton.so/view?tags=discord)_

How can I get ETH for the test net in StarkNet?

protostar is great ❤️ thanks! I'm confused about the deploy command. from which account does it deploy from? also are there no gas fees on goreli when you deploy?

I want to deploy a contract from my own argent wallet I would need to declare + sign a transaction
& I guess use the StarkCurveSigner. What are your thoughts?

_This question was originally posted on [StarkNet Discord](https://www.newton.so/view?tags=discord)_

Which account does protostar deploy command from?

Hello, is there a javascript version of StarkEx playground?

_This question was originally posted on [StarkNet Discord](https://www.newton.so/view?tags=discord)_

Is there a javascript version of StarkEx playground?

anyone has a function that converts an array of felts (numbers) to a single string in JS?

_This question was originally posted on [StarkNet Discord](https://www.newton.so/view?tags=discord)_

Do you know a function that converts an array of felts (numbers) to a single string in JS? [Cairo Lang]

hi, i used the starkgate bridge from stark to eth one hour ago. Withdrawal has not occurred yet. How many hours does the process take? My tx hash is: <address>cfa0c02d013658804505506

_This question was originally posted on [StarkNet Discord](https://www.newton.so/view?tags=discord)_

How long does starkgate bridge process?

Can tempvar be of a different type, say U256?

let's say

`tempvar foo: U256 = bar;` and bar being a U256?

_This question was originally posted on [StarkNet Discord](https://www.newton.so/view?tags=discord)_

Can tempvar be of a different type, say U256?

Hey everyone, is it possible to use argentx to sign in/authenticate user to a off-chain api/db

What I want to do is store some data off chain for each user(wallet)

I have seen that metamask/etherem has 'personal_sign' rpc method that can be used for something like this

Is there anything like this available in starknet ecosystem?

_This question was originally posted on [StarkNet Discord](https://www.newton.so/view?tags=discord)_

Is it possible to use ArgentX to sign in user to a off-chain api/db?

Hello! This is day 3 of the 17 days of the Cairo Challenge. And I have no idea how to solve the [playground](https://www.cairo-lang.org/playground/) exercise “Conditionals”. Perhaps you can help me?

```python
// The function `abs_eq` should return 1 if its inputs
// are equal or differ only in sign and 0 otherwise.
// Its current implementation is incorrect.
//
// 1. Click on "Run" to see where it fails.
// 2. Fix the body of `abs_eq`, so that the
//    program terminates successfully.

// Returns 1 if |x| = |y| (that is, x = y or x = -y),
// 0 otherwise.
func abs_eq(x: felt, y: felt) -> (bit: felt) {
    if (x == -y) {
        return (bit=1);
    } else {
        return (bit=0);
    }
}

func main() {
    let (bit) = abs_eq(2, -2);
    assert bit = 1;

    let (bit) = abs_eq(2, 3);
    assert bit = 0;

    let (bit) = abs_eq(2, 2);
    assert bit = 1;

    return ();
}
```

---


> Answers to this question are a part of the ✨ **17 days of Cairo Lang with Playground & Newton.** ✨

*Vote for your favorite answer - the best answer will win a $10 award. A new day – a new reward! During the next 17 days, our goal is to attract more developers to the Cairo language and to systematize the knowledge of Cairo lang. [Read rules](https://www.notion.so/17-days-of-Cairo-Lang-with-Newton-550dfcda6a2d449ca468be293c776578)*

How to make conditional expressions if..then..else in Cairo lang?

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