main package and main function in Go - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of a simple main function

What is the output of this Go program?

Go

package main

import "fmt"

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

A No output

B Hello, Go!

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

D hello, go!

💡 Hint

Look at what fmt.Println prints exactly.

The main function runs and prints the string exactly as given with a newline.

❓ Predict Output

intermediate

What happens if main package is missing?

What error will this Go program produce?

Go

package main

A compile error: no main function in main package

B runtime error: missing main package

C runs with no output

D compiles and prints nothing

💡 Hint

The Go compiler requires a main package with main function to run an executable.

Only package named 'main' with a main function can be compiled as an executable.

🔧 Debug

advanced

Why does this program not run?

This Go program compiles but does not run as expected. Why?

Go

package main

func Main() {
    // empty
}

A Function name must be 'main' with lowercase m

B Package name must not be 'main'

C Main function must return int

D Missing import "fmt"

💡 Hint

Go is case sensitive for function names.

The entry point must be 'main' exactly, not 'Main'.

🧠 Conceptual

advanced

Role of main package in Go

Which statement best describes the role of the main package in Go?

A It runs tests automatically

B It is used only for library code

C It automatically imports all other packages

D It defines an executable program entry point

💡 Hint

Think about what happens when you run 'go run' or 'go build'.

The main package contains the main function which is the program's entry point.

❓ Predict Output

expert

Output of multiple main functions in different files

Given two files in the same main package, what is the output when running the program? File1.go: package main import "fmt" func main() { fmt.Println("Start") helper() } File2.go: package main import "fmt" func helper() { fmt.Println("Helper called") }

A compile error: multiple main functions

B

Helper called
Start

C

Start
Helper called

D runtime error: undefined helper

💡 Hint

Functions in the same package can call each other.

The main function runs first printing 'Start', then calls helper which prints 'Helper called'.