１３日の金曜日をjson形式で出力します

jason.go

package main

import (
	"encoding/json"
	"errors"
	"fmt"
	"io/ioutil"
	"os"
)

type Jason struct {
	Year  int
	Month []int
}

func yobi(year int, month int) (int, error) {
	if year < 0 {
		return 0, errors.New("input error!!")
	}

	if month == 1 || month == 2 {
		year -= 1
		month += 12
	}
	return (year + year/4 - year/100 + year/400 + (13*month+8)/5 + 1) % 7, nil
}

func EncodingJSON(jason Jason) []byte {
	bdata, err := json.Marshal(jason)

	if err != nil {
		fmt.Println(err)
		return nil
	}
	return bdata
}

func main() {
	var (
		year       int
		pyobi      int
		jasonMonth []int
		err        error
	)
	fmt.Printf("Please, input year.->")
	fmt.Scan(&year)

	for month := 1; month <= 12; month++ {
		pyobi, err = yobi(year, month)

		if err != nil {
			fmt.Println(err)
			return
		}

		if pyobi == 0 {
			jasonMonth = append(jasonMonth, month)
		}
	}

	jason := Jason{year, jasonMonth}
	bdata := EncodingJSON(jason)
	os.Stdout.Write(bdata)

	content := []byte(bdata)
	ioutil.WriteFile("jason.json", content, os.ModePerm)
}