fn shift(c: u8, amount: u8) -> u8 {
    if c >= 97 && c <= 122 {
        return (c - 97 + amount) % 26 + 97
    }
    if c >= 65 && c <= 90 {
        return (c - 65 + amount) % 26 + 65
    }
    return c
}

pub fn main(world: World) -> Void raises {
    let source: Span<u8> = std.mem.span("Attack at Z")
    var out: [11]u8 = [0_u8; 11]
    var i: usize = 0
    while i < std.mem.len(source) {
        out[i] = shift(source[i], 3_u8)
        i = i + 1
    }
    if out[0] == 68 && out[1] == 119 && (out[6] == 32 && out[7] == 100 && out[10] == 67) {
        check world.out.write("caesar cipher ok\n")
    }
}