Validation of IIN of Kazakhstan

iin_validation.zig

const std = @import("std");
const process = std.process;

pub fn main() !void {
    var gpa = std.heap.GeneralPurposeAllocator(.{}){};
    defer _ = gpa.deinit();
    const allocator = gpa.allocator();
    const args = try std.process.argsAlloc(allocator);
    defer std.process.argsFree(allocator, args);

    if (args.len != 2) {
        const stderr = std.io.getStdErr().writer();
        try stderr.print("Usage: {s} <iin>\n", .{args[0]});
        std.process.exit(1);
    }

    const iin = args[1];
    const stdout = std.io.getStdOut().writer();
    var buf: [12]i8 = undefined;
    for (0.., iin) |i, char| {
        buf[i] =  @intCast(char - '0');
    }

    const w1 = [11]i8{1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11};
    const w2 = [11]i8{3, 4, 5, 6, 7, 8, 9, 10, 11, 1, 2};

    var checksum: i16 = multiply(buf, w1);
    if (checksum == 10) {
        checksum = multiply(buf, w2);
    }
    if (checksum != buf[11]) {
        try stdout.print("Invalid IIN\n", .{});
        std.process.exit(1);
    }
    try stdout.print("Valid IIN\n", .{});
}


pub fn multiply(iin: [12]i8, w: [11]i8) i16 {
    var result: [11]i8 = undefined;
    var checksum: i16 = 0;
    for (0..11) |i| {
        result[i] = iin[i] * w[i];
        checksum += result[i];
    }
    return @mod(checksum, 11);
}