In this case you forgot to use `assert` to set the value of a memory cell in the array.


The line in question should be:


 `assert curr_row[row_idx+1] = val;`


Then you will not have that problem


﻿  



ㅤ
_This answer was originally posted on [Triality](https://triality.org/question/1156)_

In the following function I am presented with the following error, even though my code does not make it to this function. What am I doing wrong?


`func fill_in_row{output_ptr: felt*}(row_idx : felt, row_size : felt, curr_row : felt*) {` 


 `if (row_idx == row_size-2) {`


 `return ();`


 `}`


 `let val : felt = curr_row[row_idx-1] + curr_row[row_idx];`


 `serialize_word(val);`


 `curr_row[row_idx+1] = val;`


 `return fill_in_row(row_idx+1, row_size, curr_row);`


`}`


Error: code:80:5: While expanding the reference 'curr_row' in:


 curr_row[row_idx+1] = val;


 ^******^


code:72:73: Expected a register. Found: [fp + (-4)].


ㅤ
_This question was originally posted on [Triality](https://triality.org/question/1156)_

Cairo Error: Getting Error while setting value of item in array

heyy guys, running into a problem

I have this code :
```struct TokenLedger:
   member token_address : felt
   member drip_amount : Uint256
   member balance : Uint256
end

@storage_var
func tokens_ledger(index : felt) -> (tokenLedger : TokenLedger):
end```

```let (ledger : TokenLedger) = TokenLedger(token_address, drip_amount, balance)
tokens_ledger.write(index, ledger)```
But am getting this error :

```faucet.cairo:94:34: Unexpected '.' after '__main__.TokenLedger' which is struct.
let (ledger : TokenLedger)  = TokenLedger(token_detail.token_address, token_detail.drip_amount, curr_balance)
                                ^*********^

       Failed

Error in plugin Starknet: Failed compilation of 1 contract.```

How to write a struct in storage?

I'm seeing this error when running the cairo-compile command from Setting up the Environment:


File "marshmallow_dataclass/__init__.py", line 710, in field_for_schema


`RecursionError: maximum recursion depth exceeded in comparison`


ㅤ
_This question was originally posted on [Triality](https://triality.org/question/2)_

Infinite Recursion Error on Cairo Compile

How to transpile multiple contracts at once using [Nethermind's warp](https://github.com/NethermindEth/warp)?

How to transpile multiple contracts at once using warp?

In writing my Cairo program I have the following code:


currNumber is a storage variable:


`@storage_var`


`func currNumber() -> (res : felt):`


`end`


And we have code that calls this value and uses the currNum in a subsequent function:


`...` 


 `let currNum = currNumber.read()`


 `let (res) = findSumDigits(currNum, 0)`


`...`


And I am getting the following error:


Expected expression of type 'felt', got '(res : felt)'.


 let (res) = findSumDigits(currNum, 0)


 ^*****^


﻿  



ㅤ
_This question was originally posted on [Triality](https://triality.org/question/821)_

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

Hello! This is day 13 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 “Pedersen Hash”.  Perhaps you can help me?

```
// The following code implements a Pedersen hash chain.
// Given the [Pedersen hash](https://docs.starkware.co/starkex-docs/crypto/pedersen-hash-function) function `H`, which
// takes two field elements and returns one representing their hash,
// a hash chain on inputs x_0, x_1, ..., x_n is the result of
// H(H(...H(H(x_0, x_1), x_2), ...,x_{n-1}), x_n)
// For example, the hash chain of (1, 2, 3, 4) is H(H(H(1, 2), 3), 4).
//
// Fix the function `hash_chain` to correctly implement the
// hash chain. Run your code to test it.
//
// Note: Don't use starkware.cairo.common.hash_chain (it computes the chain differently).

// Use the Pedersen builtin.
%builtins pedersen

from starkware.cairo.common.alloc import alloc
from starkware.cairo.common.cairo_builtins import HashBuiltin
from starkware.cairo.common.hash import hash2

// Computes the Pedersen hash chain on an array of size `length` starting from `data_ptr`.
func hash_chain{hash_ptr: HashBuiltin*}(data_ptr: felt*, length: felt) -> (result: felt) {
    if (length == 2) {
        let (result) = hash2(x=[data_ptr], y=[data_ptr + 1]);
        return (result=result);
    } else {
        // Fix here:
        return (result=123456);
    }
}

func main{pedersen_ptr: HashBuiltin*}() {
    alloc_locals;
    // Allocate a new array.
    let (local data_ptr: felt*) = alloc();
    // Fill the new array with field elements.
    assert [data_ptr] = 314;
    assert [data_ptr + 1] = 159;
    // Run the hash chain.
    let (result) = hash_chain{hash_ptr=pedersen_ptr}(data_ptr=data_ptr, length=2);
    // Check the result.
    assert result = 307958720726328212653290369969069617958360335228383070119367204176047090109;

    // Fill two more cells in the array.
    assert [data_ptr + 2] = 265;
    assert [data_ptr + 3] = 358;
    // Compute the hash chain on all four cells.
    let (result) = hash_chain{hash_ptr=pedersen_ptr}(data_ptr=data_ptr, length=4);
    assert result = 1828757374677754028678056220799392919487521050857166686061558043629802016816;
    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 use Pedersen Hash in StarkNet / Cairo Language?

is there anything wrong with the testnet? why is it so slow now?

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

Is there anything wrong with the testnet?

What is the proper way to declare a string in Cairo?


ㅤ
_This question was originally posted on [Triality](https://triality.org/question/573)_

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