08. Hello, World!

Go Program Order

• package statement

• imports statement

• functions, variables, constants etc.

main.go
package main
​
import "fmt"
​
func main() {
	fmt.Println("Hello, Pune!")
}

Package statement

• each go file must start with package declaration.

• package is the keyword used to declare a package.

main.go

package main

• packages are used modularity, encapsulation, separate compilation, and reuse.

• Go comes with lot of in-build library packages

• crypto - cryptography related code.

• fmt - formatted input/output related code.

• os - operation system related code.

• net/http - http related code.

Import statement

• import statements are used to import external packages.

• import is the keyword used to import a package.

main.go

import "fmt"

• before using functionality provided by any package, it needs to be imported.

• multiple packages can be imported using single import clause.

main.go
import (
	"fmt"
	"net/http"
	"os"
)

• unused imports are not allowed.

Main package

• declaring a main package is way to telling Go that this is executable and not library.

• Main package should have method named main for Go to be able to execute it.

• effectively, main is starting point for application to run from a functionality point of view.

main.go

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

Declaring a function

• function is a code block that can be called by name.

• a function is declared using func keyword followed by name of function.

• function name should be followed by round brackets ()

• every function should have function body. This is defined using opening and closing curly braces {}

• ideally, function can accept input in the form of function parameters and return output in form of return values.

main.go
func sayHello() {
	fmt.Println("Hello, Pune!")
}

Calling a function

• function that are in same package can be called directly by name.

• function is called using function name followed by ()

• functions in other packages needs to be called using package name followed by dot . and followed by function name.

main.go
func sayHello() {
	fmt.Println("Hello, Pune!")
}
func main() {
	sayHello()
}

main.go
package main
​
import "fmt"
​
func sayHello() {
	fmt.Println("Hello, Pune!")
}
func main() {
	sayHello()
	fmt.Println("Getting started is so easy")
	fmt.Println("And fun!")
}

main.go
package main
​
import "fmt"
​
func main() 

{
	fmt.Println("Hello, Pune!")
}