golang: Why do I get +Inf instead of an integer or a float?

Question

I am learning golang, working on time value of money computations

I am trying to compute for number of period to say, double your money. The formula that I am using is period = log(fv/pv) / log(1 + i). What I have so far is...

package main
import (
    "fmt"
    "math"
)
var (
    interest,
    futureValue,
    period,
    presentValue float64
)
var rate float64 = interest / 100 //converts interest into decimal... interest / 100
var ratex float64 = 1 + interest //used for (1 + i)

func main() {
    numPeriod()
}
func numPeriod() {
    fmt.Println("Enter interest amount: ")
    fmt.Scanf("%g", &interest)
    fmt.Println("Enter present value: ")
    fmt.Scanf("%g", &presentValue)
    fmt.Println("Enter future value: ")
    fmt.Scanf("%g", &futureValue)
    var logfvpvFactor float64 = futureValue / presentValue
    var logi float64 = math.Log(ratex)
    var logfvpv float64 = math.Log(logfvpvFactor)
    period = logfvpv / logi
    fmt.Printf("Number of period/s is = %g\n", period)
}

Running this, I get...

Number of period/s is = +Inf

...the answer I was looking for is either an integer or a float. How do I get that?

Thanks for your help!

Answer 1

To expand on Diego's answer, you have the line

var ratex float64 = 1 + interest

before interest is defined, so it is 0 and ratex becomes 1. Then you have the line

var logi float64 = math.Log(ratex)

and since ratex is 1, and the log of 1 is 0, logi becomes 0. You then define the period by dividing by logi, which is 0, so you will get +inf.

What you should do is assign the value to ratex after you have gotten the input for what the interest is.

Answer 2

When you assign the value of ratex, interest is 0. Therefore, the time required to increase your value will be infinity. What you want is:

func numPeriod() {
  fmt.Println("Enter interest amount: ")
    fmt.Scanf("%g", &interest)
    var ratex float64 = 1 + interest / 100 //used for (1 + i)
    fmt.Println("Enter present value: ")
    fmt.Scanf("%g", &presentValue)
    fmt.Println("Enter future value: ")
    fmt.Scanf("%g", &futureValue)
    var logfvpvFactor float64 = futureValue / presentValue
    var logi float64 = math.Log(ratex)
    var logfvpv float64 = math.Log(logfvpvFactor)
    period = logfvpv / logi
    fmt.Printf("Number of period/s is = %g\n", period)
}

Answer 3

(09:54) jnml@fsc-r550:~/src/tmp/SO/13739751$ cat main.go 
package main

import (
        "fmt"
        "math"
)

func main() {
        var i, pv, fv float64
        fmt.Println("Enter interest amount: ")
        fmt.Scanf("%g", &i)
        fmt.Println("Enter present value: ")
        fmt.Scanf("%g", &pv)
        fmt.Println("Enter future value: ")
        fmt.Scanf("%g", &fv)
        fmt.Printf("Number of period/s is = %g\n", math.Log(fv/pv)/math.Log(1+i))
}

(09:54) jnml@fsc-r550:~/src/tmp/SO/13739751$ go run main.go 
Enter interest amount: 
.1
Enter present value: 
100
Enter future value: 
200
Number of period/s is = 7.272540897341713
(09:54) jnml@fsc-r550:~/src/tmp/SO/13739751$