cairo by example

felt252

The basic data type in Cairo is felt252, which stands for field element. These are integers in the range 0 <= x < P, where P is a large prime number, currently equal to P = 2^{251} + 17 * 2^{192}+1. Field elements have the property of intentionally wrapping around when their value falls outside the specified range. That is, they use modular arithmetic.

fn main() {
    // max value of felt252
    let x: felt252 = 3618502788666131213697322783095070105623107215331596699973092056135872020480;
    let y: felt252 = 1;
    assert(x + y == 0, 'P == 0 (mod P)');
}

Since felt252 is the default data type, in simple cases like these there is no real need to specify the type. This means we can simply write:

fn main() {
    // max value of felt252
    let x = 3618502788666131213697322783095070105623107215331596699973092056135872020480;
    let y = 1;
    assert(x + y == 0, 'P == 0 (mod P)');
}