main package and main function in Go - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to declare the main package.

Go

package [1]

Drag options to blanks, or click blank then click option'

Afmt

Bhttp

Cos

Dmain

Attempts:

3 left

💡 Hint

Common Mistakes

Using other package names like 'fmt' or 'os' instead of 'main'.

Forgetting to write 'package' keyword.

The main package is declared with package main. This tells Go this is an executable program.

2fill in blank

medium

Complete the code to declare the main function.

Go

func [1]() {
    // program starts here
}

Drag options to blanks, or click blank then click option'

Amain

Bstart

Cinit

Drun

Attempts:

3 left

💡 Hint

Common Mistakes

Naming the function something other than 'main'.

Forgetting the parentheses after the function name.

The main function is declared as func main(). This is the entry point of the program.

3fill in blank

hard

Fix the error in the code to make it a valid Go program with main package and main function.

Go

package main

func [1]() {
    println("Hello, Go!")
}

Drag options to blanks, or click blank then click option'

Amain

Bhello

Cstart

DMain

Attempts:

3 left

💡 Hint

Common Mistakes

Using uppercase 'Main' instead of 'main'.

Using other function names like 'start' or 'hello'.

The main function must be named exactly 'main' with a lowercase 'm'. Go is case-sensitive.

4fill in blank

hard

Fill both blanks to create a valid Go program that prints "Welcome!".

Go

package [1]

func [2]() {
    println("Welcome!")
}

Drag options to blanks, or click blank then click option'

Amain

Bfmt

Dstart

Attempts:

3 left

💡 Hint

Common Mistakes

Using different names for package and function.

Using 'fmt' as package name which is a library, not the main package.

The package must be 'main' and the function must be 'main' to run the program.

5fill in blank

hard

Fill all three blanks to create a Go program that prints "Go is fun!" using the main package and main function.

Go

package [1]

func [2]() {
    [3]("Go is fun!")
}

Drag options to blanks, or click blank then click option'

Amain

Bprintln

Dprint

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'print' instead of 'println' which is the correct built-in function.

Using wrong package or function names.

The package and function must be 'main'. Use 'println' to print the message.

Practice

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

easy

A. It contains only variable declarations.

B. It is used to import external libraries only.

C. It defines the entry point where the program starts running.

D. It is used to define custom data types.

Solution

1. Step 1: Understand the role of the main package

   The main package is special in Go because it tells the compiler this is an executable program, not a library.

2. Step 2: Identify the program start point

   Within the main package, the main function is the starting point where execution begins.

3. Final Answer:

   It defines the entry point where the program starts running. -> Option C

4. Quick Check:

   main package = program entry [OK]

Hint: Remember: main package means program starts here [OK]

Common Mistakes:

• Thinking main package is only for imports
• Confusing main package with libraries
• Assuming main package holds only variables

2. Which of the following is the correct way to declare the main function in Go?

easy

A. func main() {}

B. function main() {}

C. def main() {}

D. main func() {}

Solution

1. Step 1: Recall Go function syntax

   In Go, functions are declared with the keyword func, followed by the function name and parentheses.

2. Step 2: Check the main function declaration

   The main function must be declared as func main() {} with no parameters and no return values.

3. Final Answer:

   func main() {} -> Option A

4. Quick Check:

   Go functions start with func [OK]

Hint: Go functions start with 'func' keyword [OK]

Common Mistakes:

• Using 'function' instead of 'func'
• Using Python or JavaScript syntax
• Placing 'func' after the function name

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

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

medium

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

B. No output, program error

C. package main

D. Hello, Go!

Solution

1. Step 1: Understand the program structure

   The program imports the fmt package and calls fmt.Println inside main to print a string.

2. Step 2: Predict the output

   The fmt.Println function prints the string with a newline, so the output is exactly: Hello, Go!

3. Final Answer:

   Hello, Go! -> Option D

4. Quick Check:

   fmt.Println prints text [OK]

Hint: fmt.Println prints text to console [OK]

Common Mistakes:

• Expecting code to print the code itself
• Confusing package name with output
• Thinking program will error without main

4. Identify the error in this Go program:

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

medium

A. main function must return a value

B. Missing import of fmt package

C. package name should not be main

D. fmt.Println syntax is incorrect

Solution

1. Step 1: Check for required imports

   The program uses fmt.Println but does not import the fmt package, which is required to use it.

2. Step 2: Understand Go import rules

   Without importing fmt, the compiler will raise an error because fmt is undefined.

3. Final Answer:

   Missing import of fmt package -> Option B

4. Quick Check:

   Use import for external packages [OK]

Hint: Always import packages before using them [OK]

Common Mistakes:

• Forgetting to import fmt
• Thinking main must return a value
• Changing package main to something else

5. You want to create a Go program that prints "Welcome!" only when run directly, but not when imported as a package. Which setup is correct?

hard

A. Use package main and define func main() { fmt.Println("Welcome!") }

B. Use package main but define func welcome() { fmt.Println("Welcome!") }

C. Use any package and define func main() { fmt.Println("Welcome!") }

D. Use package main and define func init() { fmt.Println("Welcome!") }

Solution

1. Step 1: Understand package main role

   Only programs with package main and a main function are executable directly.

2. Step 2: Identify correct function to run on start

   The main function is the entry point; code inside it runs only when program runs directly.

3. Step 3: Compare options

   Use package main and define func main() { fmt.Println("Welcome!") } uses package main and main function correctly. Use package main but define func welcome() { fmt.Println("Welcome!") } defines a different function that won't run automatically. Use any package and define func main() { fmt.Println("Welcome!") } uses any package, which won't create an executable. Use package main and define func init() { fmt.Println("Welcome!") } uses init(), which runs on import too.

4. Final Answer:

   Use package main and define func main() { fmt.Println("Welcome!") } -> Option A

5. Quick Check:

   package main + main() = executable start [OK]

Hint: Only package main with main() runs directly [OK]

Common Mistakes:

• Using init() instead of main() for start
• Using non-main package for executable
• Defining functions not named main