Go program structure - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the basic structure of a Go program?

A Go program starts with a <code>package</code> declaration, followed by import statements, and then the <code>func main()</code> function where the program execution begins.

beginner

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

The package main tells the Go compiler that this program is an executable and should have a main() function as the entry point.

beginner

Where does the execution of a Go program start?

Execution starts at the main() function inside the package main. This function is the entry point of the program.

beginner

Why do we use import statements in Go?

We use import statements to include other packages that provide useful functions and features, like fmt for printing output.

beginner

Show a simple Go program that prints "Hello, World!" and explain its parts.

Example:
<pre>package main

import "fmt"

func main() {
    fmt.Println("Hello, World!")
}</pre>
- <code>package main</code>: declares this is an executable program
- <code>import "fmt"</code>: imports the package for printing
- <code>func main()</code>: the starting point of the program
- <code>fmt.Println</code>: prints the text to the screen

What keyword starts a Go program that can be run as an executable?

A start main

B func main

C import main

D package main

The keyword package main tells Go this program is executable and needs a main() function.

Where does the Go program begin execution?

A Inside the main() function

B At the package declaration

C At the first import statement

D At the last line of code

Execution starts inside the main() function.

What is the purpose of the import statement in Go?

A To include external packages for extra features

B To declare the program's package

C To start the program

D To define variables

Import statements bring in other packages that provide useful functions.

Which package is commonly imported to print output in Go?

A io

B os

C fmt

D net

The fmt package provides functions like Println to print text.

What happens if you omit the main() function in a Go program with package main?

A The program runs normally

B The program will not compile

C The program runs but does nothing

D The program prints an error at runtime

A program with package main must have a main() function or it will not compile.

Describe the main parts of a simple Go program and their roles.

Think about what tells Go this is an executable, what brings in extra features, and where the program starts.

Explain why the main() function is important in Go programs with package main.

Consider what happens when you run a Go program.

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