Converting string input to float64 using ParseFloat in Golang

Question

I've just started learning Go and I'm trying to convert a string from standard input to a float64 so I can perform an arithmetic operation on the input value.

The output returns "0 feet converted to meters gives you 0 meters" regardless of the input value. I can't figure out why the value is zero after invoking ParseFloat on the input.

If someone could please point out to me why this is happening, I would greatly appreciate it.

const conversion float64 = 0.3048

func feetToMeters (feet float64) (meters float64) {
  return feet * conversion
}

func main(){
  fmt.Println("\n\nThis program will convert feet to meters for you!\n")

  reader := bufio.NewReader(os.Stdin)
  fmt.Println("Enter feet value: \n")
  feet, _ := reader.ReadString('\n')

  feetFloat, _ := strconv.ParseFloat(feet, 64)

  meters := feetToMeters(feetFloat)

  fmt.Printf("%v feet converted to meters give you %v meters",feetFloat,meters)
}

func main(){ fmt.Println("\n\nThis program will convert feet to meters for you!\n") feet := "35" feetFloat, _ := strconv.ParseFloat(feet, 64) meters := feetToMeters(feetFloat) fmt.Printf("%v feet converted to meters give you %v meters",feetFloat,meters) } I modified to this and it gives me the right answer. The problem ought to be with the reader. What happens if you fmt.Println(feet)? — jonathanGB
– jonathanGB, Commented Aug 4, 2016 at 22:01
Thank you @jonathanGB, I realize now that it was printing a new line character as well. — efettero
– efettero, Commented Aug 4, 2016 at 23:14
@XyMcXface Thank you for the advice. I'll have to learn about handling errors next to avoid further headache! — efettero
– efettero, Commented Aug 4, 2016 at 23:15

Toni Villena · Accepted Answer · 2016-08-04 22:23:23Z

39

The problem is that you try to parse "x.x\n", e.g: 1.8\n. And this returns an error: strconv.ParseFloat: parsing "1.8\n": invalid syntax. You can do a strings.TrimSpace function or to convert feet[:len(feet)-1] to delete \n character

With strings.TrimSpace() (you need to import strings package):

feetFloat, _ := strconv.ParseFloat(strings.TrimSpace(feet), 64)

Wtih feet[:len(feet)-1]:

feetFloat, _ := strconv.ParseFloat(feet[:len(feet)-1], 64)

Output in both cases:

10.8 feet converted to meters give you 3.2918400000000005 meters

edited Aug 4, 2016 at 22:23

answered Aug 4, 2016 at 22:08

Toni Villena

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2 Comments

efettero Over a year ago

Thank you Toni, I didn't even think about the fact that there was a new line character in the string. I appreciate you give me two solutions!

Hamza Anis Over a year ago

TrimSpace is a life savior. I thought the ParseFloat will be handling that. :)

Dmitriy · Accepted Answer · 2024-08-28 08:01:47Z

2

just tested this solution and also added one more feature:

func lbsToGrams(lbs float64) (grams float64) {
    return lbs * conversionWeight
}

Find out more on my github here

answered Aug 28, 2024 at 8:01

Dmitriy

211 bronze badge

2 Comments

Suyash Medhavi Over a year ago

This does not provide an answer to the question. Once you have sufficient reputation you will be able to comment on any post; instead, provide answers that don't require clarification from the asker. - From Review

Dmitriy Over a year ago

Thanks for checking out. It's a confirmation that the above works and it's additional golang example

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