Pathfinder acts as a trusted source of StarkNet data. Each node indepedently verifies the data it receives and ensures that it matches the proofs submitted on Ethereum. In this way, you can trust the data it provides without having to trust the StarkNet gateway or StarkWare at all.

It also provides an RPC API with which you can query StarkNet block, transaction, and event data: https://github.com/eqlabs/pathfinder#json-rpc-api

It can also be a fun first step into some of the more technical aspects underlying StarkNet. Feedback and bug reports are valuable so every node runner implicitly helps grow pathfinder and StarkNet!



Why should I run a Pathfinder node?

Hello! This is day 8 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 “Field Elements”.  Perhaps you can help me?

```
// Unlike most systems where the primitive type is a 32 or 64-bit integer,
// the primitive type in Cairo is "felt", which stands for "field element".
// When we say "a field element" we mean an integer in the range -P / 2 < x < P / 2,
// where P is a very large (prime) number.
// Currently we use a 252-bit number (76 decimal digits).
// When we add, subtract or multiply and the result is outside the range above,
// there is an overflow.
//
// The most important difference between integers and field elements is division:
// Division of field elements (and therefore division in Cairo) is not the
// integer division you may be used to.
// In the next challenge, you'll see how to use unsigned_div_rem()
// for truncated (i.e., rounding down) integer division.
//
// Make the code below output the results of the following expressions:
// 1. 1 + 100, 1 - 100, 9 * 9.
// 2. pow(10, 74), pow(10, 75), pow(10, 76)
// 3. 12 / 3, (-12) / 3
// 4. 13 / 3 (This is an example of division in the field)

%builtins output

from starkware.cairo.common.serialize import serialize_word

// Computes base^exp.
func pow(base: felt, exp: felt) -> (res: felt) {
    if (exp == 0) {
        return (res=1);
    }

    let (res) = pow(base=base, exp=exp - 1);
    return (res=res * base);
}

func main{output_ptr: felt*}() {
    serialize_word(1 + 100);
    // Add your code here.

    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 math operation with Field Elements (felts) in Cairo lang?

Hey, while using hardhat test, do we have to manually compile all the contracts again? Bcz if I don’t, it’s still using old compilation and not new contract changes.

Just trying to understand if there is a better way. In solidity, it used to auto compile and that too only changed contracts.

hardhat test

What is the difference between return and ret?


ㅤ
_This question was originally posted on [Triality](https://triality.org/question/551)_

What does ret do in Cairo?

hey! Any idea on why I get this error : `HttpError: Bad Gateway ` from `node_modules/starknet/dist/provider/default.js:217`? I may be rate limited because I am using it inside checkpoint indexer but I doubt because I dont even spam it.

Also got this : `Error: Could not POST from endpoint https://alpha4.starknet.io/feeder_gateway/call_contract?blockNumber=pending: request to https://alpha4.starknet.io/feeder_gateway/call_contract?blockNumber=pending failed, reason: socket hang up`

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

`HttpError: Bad Gateway ` from `node_modules/starknet/dist/ error in StarkNet

Hi, is there no way for me to have a struct as a `@storage_var` if it contains an array fo felts inside ?

For e.g. if I have a struct User:
```
struct User{
  values_len: felt ,
  VALUES: felt*,
}
```

Then I need to store a mapping from User Id to Users, is it not possible ?

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

Is there no way for me to have a struct as a `@storage_var` if it contains an array fo felts inside ?

i get thrown this error when deploying with v0.3.3
```[WARNING] alpha-goerli is a legacy network name parameter and it won't be supported in future versions```

Will alpha-goerli not be supported in future updates?

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

Error when deploying Cairo: [WARNING] alpha-goerli is a legacy network name parameter and it won't be supported in future versions

Just saw this in Cairo v0.10 docs: "support using functions as expressions"
Can anyone explain how does that work exactly? any example would be very helpful
It's mentioned here: https://github.com/starkware-libs/cairo-lang/releases/tag/v0.10.0#:~:text=Support%20using%20functions%20as%20expressions

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

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