Golang : Round float to precision example

Just an add on for my previous tutorial on how to round up or down a float number. For this short tutorial, we will learn how to round float numbers to certain precision.

Instead of using

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

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

 fmt.Printf("%0.2f \n", RoundUp(f, 2)) // change 2 to 5 will have no effect

 fmt.Printf("%0.2f \n", RoundDown(f, 3))  // change 3 to 4 will have no effect

which will output the precision up to 2 decimal point no matter how you instruct the Round, RoundUp and RoundDown functions.

This is because of fmt.Printf(%0.2\n) will always overrule the final display format.

To fix this problem or to display the precision properly, you will have to use fmt.Println() instead.

 var f float64 = 123.123456

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

 fmt.Println(Round(f)) // round half

 fmt.Println(RoundUp(f, 4)) // up to precision 4

 fmt.Println(RoundDown(f, 4)) // up to precision 4

Output :

123.12

123

123.1235

123.1234

Here's the full code :

 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.Println(Round(f)) // round half

  fmt.Println(RoundUp(f, 4))

  fmt.Println(RoundDown(f, 4))
 }

Reference :

https://www.socketloop.com/tutorials/golang-display-float-in-2-decimal-points-and-rounding-up-or-down