Writing first Go program

Introduction

Writing your first Go program helps you learn how to create and run simple code. It shows you the basic structure of a Go program.

When you want to learn how to write and run Go code for the first time.

When you want to test if your Go setup on your computer works correctly.

When you want to understand the basic parts of a Go program like package, import, and main function.

Syntax

Go

package main

import "fmt"

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

package main tells Go this is an executable program.

func main() is where the program starts running.

Examples

This prints a simple greeting message.

Go

package main

import "fmt"

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

You can change the message inside the quotes to print anything you want.

Go

package main

import "fmt"

func main() {
    fmt.Println("Welcome to Go programming")
}

Sample Program

This program prints the message "Hello, world!" to the screen. It shows the basic structure of a Go program.

Go

package main

import "fmt"

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

Important Notes

Always save your Go files with the .go extension.

Use the command go run filename.go to run your program in the terminal.

Make sure Go is installed and your environment is set up before running the program.

Summary

Every Go program starts with package main and a main function.

Use fmt.Println to print messages to the screen.

Running your first program helps you check your setup and understand Go basics.

Practice

1. What is the purpose of the main function in a Go program?

easy

A. It is the starting point where the program begins execution.

B. It defines a package for the program.

C. It imports external libraries.

D. It declares variables for the program.

Solution

1. Step 1: Understand the role of main function

   The main function is special in Go; it is where the program starts running.

2. Step 2: Differentiate from other parts

   Packages define code grouping, imports bring libraries, and variables store data, but none start execution.

3. Final Answer:

   It is the starting point where the program begins execution. -> Option A

4. Quick Check:

   Program starts at main() -> D [OK]

Hint: Remember: main() is the program's entry point [OK]

Common Mistakes:

• Confusing package declaration with program start
• Thinking imports start the program
• Assuming variables control program flow

2. Which of the following is the correct way to print "Hello, Go!" in a Go program?

easy

A. fmt.Println("Hello, Go!")

B. print("Hello, Go!")

C. fmt.print("Hello, Go!")

D. console.log("Hello, Go!")

Solution

1. Step 1: Identify the correct print function in Go

   Go uses the fmt package with Println to print with a newline.

2. Step 2: Check syntax correctness

   fmt.Println("Hello, Go!") is correct; others are either wrong function names or from other languages.

3. Final Answer:

   fmt.Println("Hello, Go!") -> Option A

4. Quick Check:

   Use fmt.Println() to print lines in Go [OK]

Hint: Use fmt.Println() for printing with newline [OK]

Common Mistakes:

• Using fmt.print instead of fmt.Println
• Using print() which is not standard in Go
• Using console.log from JavaScript

3. What will be the output of this Go program?

package main
import "fmt"
func main() {
    fmt.Println("Welcome to Go!")
}

medium

A. package main
import "fmt"
func main() {
fmt.Println("Welcome to Go!")
}

B. fmt.Println("Welcome to Go!")

C. Welcome to Go!

D. Error: missing main function

Solution

1. Step 1: Understand program structure

   The program imports fmt and defines main(), which prints the string.

2. Step 2: Identify output of fmt.Println

   It prints the string exactly: Welcome to Go! with a newline.

3. Final Answer:

   Welcome to Go! -> Option C

4. Quick Check:

   fmt.Println prints string output [OK]

Hint: fmt.Println prints the string content, not code [OK]

Common Mistakes:

• Confusing code with output
• Expecting code to print itself
• Thinking main function is missing

4. Identify the error in this Go program:

package main
import "fmt"
func main() {
    fmt.Println("Hello, world!"
}

medium

A. Missing import statement

B. Incorrect function name

C. Missing package declaration

D. Missing closing parenthesis in fmt.Println call

Solution

1. Step 1: Check syntax of fmt.Println

   The call to fmt.Println is missing a closing parenthesis at the end.

2. Step 2: Verify other parts

   Package and import are present, function name is correct, so no errors there.

3. Final Answer:

   Missing closing parenthesis in fmt.Println call -> Option D

4. Quick Check:

   Check parentheses in function calls [OK]

Hint: Count opening and closing parentheses carefully [OK]

Common Mistakes:

• Forgetting closing parenthesis in function calls
• Assuming missing import or package causes this error
• Misnaming main function

5. You want to write a Go program that prints "Hello" on one line and "World" on the next line. Which code snippet achieves this correctly?

hard

A. package main
import "fmt"
func main() {
fmt.Print("Hello\nWorld")
}

B. package main
import "fmt"
func main() {
fmt.Println("Hello")
fmt.Println("World")
}

C. package main
import "fmt"
func main() {
fmt.Println("Hello\nWorld")
}

D. package main
import "fmt"
func main() {
fmt.Print("Hello")
fmt.Print("World")
}

Solution

1. Step 1: Understand printing with new lines

   fmt.Println prints text and adds a newline automatically.

2. Step 2: Check each option's output

   A: Two fmt.Println calls print "Hello" on one line and "World" on the next. Correct.
   B: fmt.Print("Hello\nWorld") prints "Hello\nWorld" (with actual newline) on one line.
   C: fmt.Println("Hello\nWorld") prints "Hello\nWorld" (with actual newline) followed by newline, so output is two lines.
   D: Two fmt.Print calls print "HelloWorld" on one line.

3. Final Answer:

   package main import "fmt" func main() { fmt.Println("Hello") fmt.Println("World") } -> Option B

4. Quick Check:

   Use fmt.Println twice for separate lines [OK]

Hint: Use fmt.Println for each line to print separately [OK]

Common Mistakes:

• Using fmt.Print without newline causes joined output
• Expecting \n inside fmt.Println to create new line
• Confusing fmt.Print and fmt.Println behavior