Understanding Go Program Structure

Every Go program follows a clear and consistent structure with these main components:

1. Package Declaration: Every Go file starts with a package declaration
2. Import Statements: Required packages are imported
3. Global Variables/Constants (optional): Declarations accessible throughout the package
4. Functions: Including the mandatory main() function for executable programs

Your First Go Program

Let's write the classic "Hello, World!" program to understand these components:

// File: main.go
package main

import "fmt"

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

Code Breakdown

1. Package Declaration (package main)

   • Every Go file must start with a package declaration
   • The main package is special - it tells Go this is an executable program
   • All files in the same directory must belong to the same package

2. Import Statement (import "fmt")

   • Imports the formatting package from Go's standard library
   • fmt provides functions for formatted I/O operations
   • Go's standard library is rich with useful packages

3. Main Function (func main())

   • Entry point of the program
   • Must be in the main package
   • Takes no arguments and returns no values
   • Program starts executing from here

Key Go Syntax Features

1. No Semicolons

   • Go automatically inserts semicolons at the end of statements
   • Don't use semicolons in your code (except in for loops)

2. Code Formatting

   • Go enforces a standard code format
   • Use go fmt to automatically format your code

Running Your Program

1. Save the Code

   • Create a new file named main.go
   • Copy the code above into the file

2. Run the Program

   # Run directly
   $ go run main.go
   Hello, World!
   
   # Or build and run
   $ go build main.go
   $ ./main
   Hello, World!
   

3. Understanding Build Commands

   • go run: Compiles and runs in one step (good for development)
   • go build: Creates an executable (good for deployment)

Common Beginner Tips

1. File Organization

   • Keep one package per directory
   • Use meaningful file names
   • Main package should be in the project root

2. Code Style

   • Use go fmt before committing code
   • Follow Go's official style guide
   • Keep functions small and focused