Go program structure - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of a simple Go program

What is the output of this Go program?

Go

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

A Compilation error

B hello, go!

C Hello Go!

D Hello, Go!

💡 Hint

Look at the exact string inside fmt.Println and remember Go is case-sensitive.

The program prints exactly what is inside the quotes with correct capitalization.

❓ Predict Output

intermediate

Variable declaration and output

What will this Go program print?

Go

package main
import "fmt"
func main() {
    var x int = 5
    fmt.Println(x)
}

A Compilation error

B 5

C 0

D x

💡 Hint

The variable x is assigned 5 before printing.

The program prints the value of x, which is 5.

❓ Predict Output

advanced

Understanding package and import

What error does this Go program produce?

Go

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

A undefined: fmt

B no error, prints Hi

C syntax error: missing import

D runtime error

💡 Hint

Check if the fmt package is imported before using it.

The program uses fmt.Println but does not import fmt, causing undefined error.

❓ Predict Output

advanced

Multiple functions and main execution

What is the output of this Go program?

Go

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

A

Hello
World

B

World
Hello

C Hello World

D Compilation error

💡 Hint

Functions run in the order they are called inside main.

The greet function prints Hello, then main prints World on a new line.

🧠 Conceptual

expert

Go program entry point and package rules

Which statement about Go program structure is correct?

A The main() function can be in any package, not necessarily main.

B Go programs can run without a main() function if package main is present.

C Every Go executable program must have package main and a main() function.

D Packages are optional in Go programs.

💡 Hint

Think about what Go requires to start running a program.

Go requires package main and main() as the entry point for executables.

Practice

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

easy

A. It is the entry point where the program starts running.

B. It declares the package name.

C. It imports external libraries.

D. It defines variables globally.

Solution

1. Step 1: Understand the role of main function

   The main function is where the Go program begins execution.

2. Step 2: Differentiate from other parts

   Package declaration and imports do not run code; only main runs the program.

3. Final Answer:

   It is the entry point where the program starts running. -> Option A

4. Quick Check:

   Main function = program start [OK]

Hint: Main function always starts the Go program [OK]

Common Mistakes:

• Confusing package declaration with program start
• Thinking imports run code
• Assuming variables run the program

2. Which of the following is the correct way to start a Go program file?

easy

A. import "fmt"

B. func main() { }

C. package main

D. var main = 1

Solution

1. Step 1: Identify the first line in a Go program

   Every Go program starts with a package declaration, usually package main for executable programs.

2. Step 2: Check other options

   func main() is a function, not the first line. import comes after package. var main is invalid as a start.

3. Final Answer:

   package main -> Option C

4. Quick Check:

   Package declaration first = package main [OK]

Hint: Go files start with package declaration [OK]

Common Mistakes:

• Starting with function before package
• Using import before package
• Declaring variables as first line

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

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

medium

A. Hello, Go!

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

C. package main

D. Syntax error

Solution

1. Step 1: Understand the code structure

   The program imports fmt and calls fmt.Println to print a string.

2. Step 2: Predict the output

   The output will be the string inside Println: "Hello, Go!" printed on the screen.

3. Final Answer:

   Hello, Go! -> Option A

4. Quick Check:

   Println outputs string = Hello, Go! [OK]

Hint: Println prints the string inside quotes [OK]

Common Mistakes:

• Confusing code with output
• Expecting package or import to print
• Thinking syntax error without reason

4. Identify the error in this Go program:

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

medium

A. Missing package declaration

B. Incorrect import syntax

C. Missing main function

D. Println should be fmt.Println

Solution

1. Step 1: Check function call

   The code calls Println without prefix. In Go, Println is in fmt package, so it must be fmt.Println.

2. Step 2: Verify other parts

   Package and import are correct. Main function exists. Import syntax is correct.

3. Final Answer:

   Println should be fmt.Println -> Option D

4. Quick Check:

   Use fmt.Println, not just Println [OK]

Hint: Always prefix Println with fmt. [OK]

Common Mistakes:

• Calling Println without fmt prefix
• Removing package declaration
• Forgetting main function

5. You want to write a Go program that prints "Welcome!" but you forgot the package main line. What will happen when you try to run it?

hard

A. The program will run and print "Welcome!"

B. The compiler will show an error about missing package declaration

C. The program will print nothing but run successfully

D. The program will run but ignore the main function

Solution

1. Step 1: Understand Go program requirements

   Every Go program must start with a package declaration, usually package main for executables.

2. Step 2: Predict compiler behavior

   Without package main, the compiler will report an error and refuse to build the program.

3. Final Answer:

   The compiler will show an error about missing package declaration -> Option B

4. Quick Check:

   Missing package line causes compile error [OK]

Hint: Package main is mandatory for executable programs [OK]

Common Mistakes:

• Assuming program runs without package
• Thinking main function alone is enough
• Ignoring compiler errors