Packages: The Standard library

While your code lives in the main package, you can import and use code from other packages, the most common of which will be the Go standard library.

Go comes with a rich standard library full of useful packages you can import.

The import Statement

To use code from another package, you need to import it:

package main

import "fmt"

func main() {
    fmt.Println("Hello, World!")
}

The import "fmt" statement tells Go you want to use the fmt package.

Using Imported Packages

Once imported, you access a package's functions using the package name, a dot, and the function name:

package main

import "fmt"

func main() {
    fmt.Println("This uses the fmt package")
    fmt.Print("So does this")
}

The pattern is: packageName.FunctionName()

Importing Multiple Packages

You can import multiple packages using parentheses:

package main

import (
    "fmt"
    "strings"
)

func main() {
    name := "goku"
    upper := strings.ToUpper(name)
    fmt.Println(upper)
}
// Output: GOKU

This is cleaner than writing multiple import statements.

The strings Package

The strings package provides functions for working with text:

package main

import (
    "fmt"
    "strings"
)

func main() {
    // Convert to uppercase
    fmt.Println(strings.ToUpper("hello"))  // HELLO
    
    // Convert to lowercase
    fmt.Println(strings.ToLower("WORLD"))  // world
    
    // Check if string contains substring
    fmt.Println(strings.Contains("Goku", "ok"))  // true
    
    // Count occurrences
    fmt.Println(strings   

The math Package

The math package provides mathematical operations:

package main

import (
    "fmt"
    "math"
)

func main() {
    // Power
    fmt.Println(math.Pow(2, 10))  // 1024
    
    // Square root
    fmt.Println(math.Sqrt(16))  // 4
    
    // Absolute value
    fmt.Println(math.Abs(-42))  // 42
    
    // Maximum of two numbers
    fmt.Println(math   

Package Names Match Import Paths

The name you use to call functions matches the import path:

import "fmt"          // Use as: fmt.Println()
import "strings"      // Use as: strings.ToUpper()
import "math"         // Use as: math.Pow()

You Must Use What You Import

Go will give a compilation error if you import a package but don't use it:

package main

import "fmt"
import "strings"  // ERROR: imported and not used

func main() {
    fmt.Println("Hello")
    // Not using strings, so this causes an error
}

Only import what you actually need!

Common Standard Library Packages

Here are some useful packages from Go's standard library:

• fmt - Formatting and printing
• strings - String manipulation
• math - Mathematical operations
• strconv - Converting strings to/from other types
• time - Working with dates and times
• os - Operating system functionality

Assignment

For this challenge, use the strings and math packages together.

Your task:

1. Import fmt, math and strings packages
2. Use the strings.ToUpper() function to convert the name parameter in the first function to uppercase and return it
3. Use the math.Sqrt() function to convert the powerLevel parameter in the second function to it's sqrt and return it.