00_Cairo program entry point

Jul 4, 2023159

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This article discusses the entry point of the Cairo program and provides examples in both single-file Cairo programs and Starknet smart contracts. It mentions that the Cairo compiler version used is 2.0.0-rc0 and acknowledges that syntax may vary in different versions. The main function is highlighted as the entry point in Cairo programs, and an example of a main function with a return value is provided. The article also briefly mentions the entry point for Starknet smart contracts using the #[starknet::contract] annotation.

00_Cairo Program Entry#

The version of the Cairo compiler used in this article is 2.0.0-rc0. Since Cairo is being updated rapidly, there may be slight differences in syntax between different versions. The article will be updated to a stable version in the future.

Entry Point for Single-File Cairo Programs#

Similar to most programming languages, the entry point for a single-file Cairo program is the main function.

use debug::PrintTrait;

const ONE_HOUR_IN_SECONDS: felt252 = 3600;

fn main(){
    ONE_HOUR_IN_SECONDS.print();
}

To run the program, use the following command:

cairo-run $file_path

The main function can have a return value, as shown below:

fn main() -> felt252 {
   return 10; 
}

The return value will be output within square brackets on this line:

Run completed successfully, returning [10]

Entry Point for Starknet Smart Contracts#

Start with #[starknet::contract], and add the contract name after the mod keyword.

#[starknet::contract]
mod ERC20 {
	...
}