golang中的浮点数返回零(Float return zero in golang)

Why does this code always return zero:

package main

import "fmt"

func main() {
    var index_of_array int
    fmt.Scan(&index_of_array)
    var arr = make([]int, index_of_array)
    for i := 0; i < len(arr); i++ {
        fmt.Scan(&arr[i])
    }

    positive := 0
    negative := 0
    zero_ := 0
    for _, arr_v := range arr {
        if arr_v > 0 {
            positive++
        } else if arr_v < 0 {
            negative++
        } else if arr_v == 0 {
            zero_++
        }
    }

    fmt.Printf("%f ", float32(positive/len(arr)))
    fmt.Printf("%f ", float32(negative/len(arr)))
    fmt.Printf("%f ", float32(zero_/len(arr)))

}

i mean to output

A decimal representing of the fraction of positive numbers in the array. A decimal representing of the fraction of negative numbers in the array. A decimal representing of the fraction of zeroes in the array.

Sample Input

-4 3 -9 0 4 1

Sample Output

0.500000

0.333333

0.166667

but in my code the output like this with the same input

0.000000