Solution: circle STDIN with math

Of course you don't need to type in the value if PI yourself. There is a module called math that provides you the value at a much better precision. There is also a function called Pow that can rasie any number to any power.

package main

import (

func main() {

    var radiusStr string
    fmt.Print("radius: ")

    radius, err := strconv.ParseFloat(radiusStr, 64)
    if err == nil {
        area := math.Pi * math.Pow(radius, 2)
        circumference := 2 * math.Pi * radius
        fmt.Printf("Area: %v\n", area)
        fmt.Printf("Cirumference: %v\n", circumference)