POST to localhost:8080/change with {given: 1000, owed: 450} and receive a JSON response of the change due in standard US currency. Some DRYing should occur around the Denominations.

gistfile1.go

package main

import (
	"encoding/json"
	"io"
	"log"
	"net/http"
	"strconv"
)

type Denomination struct {
	Name  string
	Value int
	Count int
}

type Change struct {
	Given         int
	Owed          int
	_Left         int
	Denominations []*Denomination
}

func (c *Change) Deduct(d *Denomination) {
	flag := true

	for flag {
		if c._Left >= d.Value {
			c._Left -= d.Value
			d.Count += 1
		} else {
			flag = false
		}
	}
}

func (c *Change) ToJSON() ([]byte, error) {
	data := make(map[string]int)

	for i := 0; i < len(c.Denominations); i++ {
		d := c.Denominations[i]
		if d.Count > 0 {
			data[d.Name] = d.Count
		}
	}

	return json.Marshal(data)
}

func (c *Change) InitDenominations() {
	c.Denominations = append(c.Denominations, &Denomination{Name: "Hundred", Value: 10000, Count: 0})
	c.Denominations = append(c.Denominations, &Denomination{Name: "Fifty", Value: 5000, Count: 0})
	c.Denominations = append(c.Denominations, &Denomination{Name: "Twenty", Value: 2000, Count: 0})
	c.Denominations = append(c.Denominations, &Denomination{Name: "Ten", Value: 1000, Count: 0})
	c.Denominations = append(c.Denominations, &Denomination{Name: "Five", Value: 500, Count: 0})
	c.Denominations = append(c.Denominations, &Denomination{Name: "One", Value: 100, Count: 0})
	c.Denominations = append(c.Denominations, &Denomination{Name: "Quarter", Value: 25, Count: 0})
	c.Denominations = append(c.Denominations, &Denomination{Name: "Dime", Value: 10, Count: 0})
	c.Denominations = append(c.Denominations, &Denomination{Name: "Nickel", Value: 5, Count: 0})
	c.Denominations = append(c.Denominations, &Denomination{Name: "Penny", Value: 1, Count: 0})
}

func MakeChange(Given int, Owed int) *Change {
	c := &Change{Given: Given, Owed: Owed}
	c.InitDenominations()

	c._Left = c.Given - c.Owed

	for i := 0; i < len(c.Denominations); i++ {
		c.Deduct(c.Denominations[i])
	}

	return c
}

func changeHandler(w http.ResponseWriter, r *http.Request) {
	given, _ := strconv.Atoi(r.FormValue("given"))
	owed, _ := strconv.Atoi(r.FormValue("owed"))
	json, _ := MakeChange(given, owed).ToJSON()
	w.Header().Set("Content-Type", "application/json")
	io.WriteString(w, string(json))
}

func main() {
	http.HandleFunc("/change", changeHandler)
	log.Fatal(http.ListenAndServe(":8080", nil))
}

I need to DRY the areas around Denomination along with add more proper error handling.