Golang : Display float in 2 decimal points and rounding up or down

We will cover 2 items for this tutorial.

First, we will learn how to display a float number in decimal points with the fmt.Printf() function. The %0.2f inside fmt.Printf() function tells Golang to display up to 2 decimal points. To increase the precision, simply adjust the number from %0.2f to %0.#f. # being the number of digits to display the after the decimal point.

Next, Golang math package lacks of functions to do rounding on float numbers. The code example below has 3 functions - one to do rounding, next for rounding up and another to do rounding down for a float value.

Here you go!

 package main

 import (
  "fmt"
  "math"
 )

 func Round(input float64) float64 {
  if input < 0 {
 return math.Ceil(input - 0.5)
  }
  return math.Floor(input + 0.5)
 }

 func RoundUp(input float64, places int) (newVal float64) {
  var round float64
  pow := math.Pow(10, float64(places))
  digit := pow * input
  round = math.Ceil(digit)
  newVal = round / pow
  return
 }

 func RoundDown(input float64, places int) (newVal float64) {
  var round float64
  pow := math.Pow(10, float64(places))
  digit := pow * input
  round = math.Floor(digit)
  newVal = round / pow
  return
 }

 func main() {
  var f float64 = 123.123456

  fmt.Printf("%0.2f \n", f)

  fmt.Printf("%0.2f \n", Round(f)) // round half

  fmt.Printf("%0.2f \n", RoundUp(f, 2))

  fmt.Printf("%0.2f \n", RoundDown(f, 2))

 }

NOTE : Change value of f to -123.123456 and see how it goes.

Output :

123.12

123.00

123.13

123.12

References :

http://golang.org/pkg/math/#Ceil

http://golang.org/pkg/math/#Floor

https://gist.github.com/DavidVaini/10308388