📐 Go Program Structure – Get Started with Your First Go Program

🧲 Introduction – How Go Code is Organized

Every Go program, no matter how simple or complex, follows a consistent structure that ensures readability, maintainability, and easy compilation. Understanding the Go program structure is the first step toward writing clean, idiomatic Go code.

🎯 In this section, you’ll learn:

• The layout of a typical Go program
• Mandatory components like package main and func main()
• How to use packages and comments effectively
• How to compile and execute a Go file

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🔧 Basic Go Program Layout

Let’s look at the classic “Hello, World!” program in Go:

package main

import "fmt"

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

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🧩 Explanation of Each Component

Part	Description
package main	Declares this file as part of the main package (needed to compile and run as an executable).
import "fmt"	Brings in the fmt package from Go’s standard library, used for formatted I/O.
func main()	Entry point of the program. The Go runtime executes this function first.
fmt.Println(...)	Prints output to the console. In this case, it prints “Hello, World!”

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🗂️ File Extension and Naming

• Every Go source file must have the .go extension.
• The file name can be anything, but the main package must have a main() function.
• Go programs are case-sensitive.

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🧪 Compiling & Running a Go Program

Once you’ve written your code in hello.go, follow these steps:

# Run without compiling permanently
go run hello.go

Output:

Hello, World!

To compile it into a binary:

go build hello.go

This creates an executable:

• hello on Linux/macOS
• hello.exe on Windows

Run it:

./hello

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✍️ Adding Comments in Go

Go supports two styles of comments:

// Single-line comment

/*
Multi-line comment
that spans multiple lines
*/

Use comments to explain logic, disable code, or document sections. Go also uses comments for documentation generation via godoc.

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🔍 More About the main Function

• Go does not allow overloading, so there’s only one main() function.
• Any file in package main that contains func main() can act as the entry point.
• A Go program won’t compile without this setup for executables.

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✅ Example: Command-Line Arguments

package main

import (
    "fmt"
    "os"
)

func main() {
    if len(os.Args) < 2 {
        fmt.Println("Usage: go run main.go <yourname>")
        return
    }

    name := os.Args[1]
    fmt.Println("Hello,", name)
}

Run:

go run main.go John

Output:

Hello, John

🧠 os.Args[0] is always the executable name. User arguments start from index 1.

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📌 Summary – Recap & Next Steps

You’ve now learned the foundational structure of a Go program, from package declarations to running executables. This knowledge forms the backbone of writing real-world Go applications.

🔍 Key Takeaways:

• Every Go program starts with package main and func main()
• Use the import keyword to access libraries
• Use go run or go build to execute your code
• Comments in Go are simple and used for documentation and clarity

⚙️ Next: Learn about Go’s basic syntax, variable declarations, and type system.

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❓ FAQs – Go Program Structure

❓ Why do I need package main?
✅ It defines the program as an executable entry point. Without it, Go will compile the file as a library, not a runnable program.

❓ Can I have multiple main() functions?
✅ No. Only one main() is allowed per main package. However, you can have multiple Go files under the same package.

❓ What is the use of import in Go?
✅ It allows you to include other packages (standard or custom) to access additional functions and types.

❓ How do I print in Go?
✅ Use the fmt package’s Println, Printf, or Print functions.

❓ What if I don’t include a main() function?
✅ Your code will compile as a package, but it won’t run. main() is mandatory in any Go executable.

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