# Golang : How to convert a number to words

I need to translate a given number into words such as `100`

to `one hundred`

. The code below is a translation of Christian d'Heureuse's work at http://www.source-code.biz/snippets/java/13.htm. It shows how to convert a number up to billion into words.

Here you go!

```
package main
import (
"fmt"
)
var lowNames = []string{"zero", "one", "two", "three", "four", "five", "six", "seven", "eight", "nine", "ten", "eleven", "twelve", "thirteen", "fourteen", "fifteen", "sixteen", "seventeen", "eighteen", "nineteen"}
var tensNames = []string{"twenty", "thirty", "forty", "fifty", "sixty", "seventy", "eighty", "ninety"}
var bigNames = []string{"thousand", "million", "billion"}
func convert999(num int) string {
s1 := lowNames[num/100] + " hundred"
s2 := convert99(num % 100)
if num <= 99 {
return s2
}
if num0 == 0 {
return s1
} else {
return s1 + " " + s2
}
}
func convert99(num int) string {
if num < 20 {
return lowNames[num]
}
s := tensNames[num/10-2]
if num == 0 {
return s
}
return s + "-" + lowNames[num]
}
func convertNum2Words(num int) string {
if num < 0 {
return "negative " + convertNum2Words(-num)
}
if num <= 999 {
return convert999(num)
}
s := ""
t := 0
for num > 0 {
if num00 != 0 {
s2 := convert999(num % 1000)
if t > 0 {
s2 = s2 + " " + bigNames[t-1]
}
if s == "" {
s = s2
} else {
s = s2 + ", " + s
}
}
num /= 1000
t++
}
return s
}
func main() {
fmt.Println("100 in words : ", convertNum2Words(100))
fmt.Println("0123 in words : ", convertNum2Words(0123))
fmt.Println("-99 in words : ", convertNum2Words(-99))
fmt.Println("54312337 in words : ", convertNum2Words(54312337))
fmt.Println("932476182910 in words : ", convertNum2Words(932476182910))
fmt.Println("-932476182910 in words : ", convertNum2Words(-932476182910))
// because we only convert up to billion, any number exceeding 9 zeros will cause
// runtime error: index out of range
//fmt.Println("9324761829101 in words : " , convertNum2Words(9324761829101))
}
```

Output:

100 in words : one hundred

0123 in words : eighty-three <------ wrong!

-99 in words : negative ninety-nine

54312337 in words : fifty-four million, three hundred twelve thousand, three hundred thirty-seven

932476182910 in words : nine hundred thirty-two billion, four hundred seventy-six million, one hundred eighty-two thousand, nine hundred ten

-932476182910 in words : negative nine hundred thirty-two billion, four hundred seventy-six million, one hundred eighty-two thousand, nine hundred ten

**NOTES:**

You need to put in a sanity checker to test if the input number is a sane number. As demonstrated, having a given number that starts with zero will cause the translation to go crazy. For example, the translation of `0123`

to `eighty-three`

just doesn't make sense.

How to write the sanity checker? That's the exercise for this tutorial. ;-)

**Reference:**

http://www.source-code.biz/snippets/java/13.htm

Tags : golang translate-number-to-words convert-number

##### By Adam Ng

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