At this moment there is not any console logging. It is not possible to make a function

```
func main(y: felt) {
    // print value of y here
}

```
in Cairo 1

Newton

I have a question about how to print "Hello World" in Cairo 1. How do I log/print ?

How do I log/print in Cairo 1.0?

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?

### *From Newton AI*
*OpenZeppelin is a collection of reusable, secure smart contract libraries for Ethereum. It provides a set of Solidity contracts that implement common contract patterns and functions, such as ERC20 token contracts and contracts for managing and securing user accounts. By using OpenZeppelin libraries in your contracts, you can benefit from the security and functionality provided by these pre-written contracts, without having to reimplement them yourself. When transpiling your contracts, the transpiler will include the code from any imported libraries, such as OpenZeppelin, in the final transpiled output.*

Is it possible to transpile contracts that use openzeppelin libraries?

What resources are required to run a Pathfinder node?

How can I use the meta-class of contract (starknetjs) for interaction?

How can I use meta-class of contract (starknetjs) for interaction?


What kind of efficiency gains can one expect from writing the contracts directly in Cairo as opposed to transpiling with warp?

What are the efficiency gains of direct Cairo vs. transpiling with warp?

Hey, the docs always use `await` before methods, but when I try to run those scripts I get an error. 

Anyone could help?

How to use await in StarkNet.py?

I am getting the error above when I use the following line:


`let local (prev : felt) = fibonacci(n-1)`


ㅤ
_This question was originally posted on [Triality](https://triality.org/question/582)_

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