# Golang : Calculate diameter, circumference, area, sphere surface and volume

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Let's travel back to high school for a while and learn some physics. We will learn how to calculate a circle's area, diameter, circumference, sphere surface and sphere volume the proper way. I saw many programmers calculate the sphere volume the wrong way in Golang. While the result might appear to be correct mathematically, but wrong. A simple division by float or integer will make a big difference in the sphere volume result. 4/3 is not the same as 4/3.0. The code below will demonstrate the differences and as a programmer, it is our job to look out for a simple mistake such as this. You never know in future, some one's life might depend on your code. Here you go! package main import ( "fmt" "math" ) var ( radius, diameter, circumference, area, sphereSurface, sphereVolume float64 ) func main() { fmt.Println("Enter the radius of a circle (in meter): ") _, err := fmt.Scanf("%f", &radius) if err != nil { fmt.Println(err) fmt.Println("You have entered radius of : ", radius) diameter = 2 * radius circumference = 2 * math.Pi * radius area = math.Pi * math.Pow(radius, 2) sphereSurface = 4 * math.Pi * math.Pow(radius, 2) // Go to be careful here, casting float64 over 4/3 is pointless // because 4/3 is still 1 // The correct way is to do 4.0/3.0 sphereVolume = float64((4.0 / 3.0)) * (math.Pi * math.Pow(radius, 3)) // this will give wrong result //sphereVolume = 4 / 3 * math.Pi * radius * radius * radius fmt.Println("Diameter (m) : ", diameter) fmt.Println("Circumference (m): ", circumference) fmt.Println("Area (m2) : ", area) fmt.Println("Sphere surface (m2) : ", sphereSurface) fmt.Println("Sphere volume (m3) [correct way] : ", sphereVolume) sphereVolume = 4 / 3 * math.Pi * radius * radius * radius // <--- WRONG! fmt.Println("Sphere volume (m3) [wrong way] : ", sphereVolume) // compare your calculation result with // result from http://www.rkm.com.au/CALCULATORS/CALCULATOR-circle-sphere.html // and http://www.calculatorsoup.com/calculators/geometry-solids/sphere.php Output: Enter the radius of a circle (in meter): 5 You have entered radius of : 5 Diameter (m) : 10 Circumference (m): 31.41592653589793 Area (m2) : 78.53981633974483 Sphere surface (m2) : 314.1592653589793 Sphere volume (m3) [correct way] : 523.5987755982987 Sphere volume (m3) [wrong way] : 392.69908169872417 References: http://www.rkm.com.au/CALCULATORS/CALCULATOR-circle-sphere.html

#### See also : Golang : Find change in a combination of coins example

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##### By Adam Ng

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