Why error handling is required in Go - Test Your Understanding

Practice - 5 Tasks

1fill in blank

easy

Complete the code to check if an error occurred after opening a file.

Go

file, err := os.Open("test.txt")
if [1] != nil {
    fmt.Println("Error opening file")
}

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

Afile

Berr

Cnil

Dos

Attempts:

3 left

💡 Hint

Common Mistakes

Checking the wrong variable for error

Not checking for nil before using the file

In Go, errors are returned as the second value. We check if err is not nil to detect an error.

2fill in blank

medium

Complete the code to handle an error returned by a function.

Go

result, [1] := divide(10, 0)
if err != nil {
    fmt.Println("Cannot divide by zero")
}

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

Afail

Berror

Ce

Derr

Attempts:

3 left

💡 Hint

Common Mistakes

Using a variable name other than 'err' for errors

Ignoring the error variable

The error variable is commonly named err in Go to follow conventions and clarity.

3fill in blank

hard

Fix the error in the code that ignores error handling.

Go

file, _ := os.Open("data.txt")
[1] := file.Stat()
fmt.Println(info.Size())

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

Ainfo, err

BfileInfo

Cinfo

DfileInfo, err

Attempts:

3 left

💡 Hint

Common Mistakes

Ignoring the error returned by Stat

Using undefined variable 'info' without assignment

To handle errors properly, assign both the returned info and error from file.Stat(). This allows checking the error before using info.

4fill in blank

hard

Fill both blanks to correctly handle an error when reading a file.

Go

data, [1] := os.ReadFile("config.json")
if [2] != nil {
    fmt.Println("Failed to read file")
}

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

Aerr

Berror

Cfail

De

Attempts:

3 left

💡 Hint

Common Mistakes

Using different variable names for error capture and check

Not checking the error at all

Use the variable err to capture and check the error returned by os.ReadFile.

5fill in blank

hard

Fill all three blanks to handle an error and print the file size.

Go

file, [1] := os.Open("log.txt")
if [2] != nil {
    fmt.Println("Error opening file")
    return
}
info, [3] := file.Stat()

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

Aerr

Berror

Cerr2

Dfail

Attempts:

3 left

💡 Hint

Common Mistakes

Using different variable names for errors

Not checking errors before using file info

Use err consistently to capture and check errors from both os.Open and file.Stat().

Practice

1. Why is error handling important in Go programs?

easy

A. It makes the program run faster by skipping checks.

B. It removes the need to write any tests.

C. It automatically fixes all bugs in the code.

D. It helps the program continue running even when something unexpected happens.

Solution

1. Step 1: Understand the role of error handling

   Error handling is used to manage unexpected problems during program execution.

2. Step 2: Identify the benefit in Go programs

   By handling errors, the program can avoid crashing and continue working smoothly.

3. Final Answer:

   It helps the program continue running even when something unexpected happens. -> Option D

4. Quick Check:

   Error handling = program stability [OK]

Hint: Error handling keeps programs stable during problems [OK]

Common Mistakes:

• Thinking error handling speeds up code
• Believing error handling fixes bugs automatically
• Assuming error handling removes need for testing

2. Which of the following is the correct way to check an error returned by a function in Go?

easy

A. if err = nil { // handle error }

B. if err != nil { // handle error }

C. if error != nil { // handle error }

D. if err == nil { // handle error }

Solution

1. Step 1: Recall Go error checking syntax

   In Go, errors are checked by comparing the error variable to nil.

2. Step 2: Identify correct syntax

   The correct check is if err != nil, meaning an error occurred.

3. Final Answer:

   if err != nil { // handle error } -> Option B

4. Quick Check:

   Check error with '!= nil' [OK]

Hint: Always check if err is NOT nil to catch errors [OK]

Common Mistakes:

• Using '==' instead of '!=' to check errors
• Using wrong variable name like 'error'
• Assigning instead of comparing with '='

3. What will be the output of this Go code snippet?

package main
import (
  "errors"
  "fmt"
)
func divide(a, b int) (int, error) {
  if b == 0 {
    return 0, errors.New("cannot divide by zero")
  }
  return a / b, nil
}
func main() {
  result, err := divide(10, 0)
  if err != nil {
    fmt.Println(err)
  } else {
    fmt.Println(result)
  }
}

medium

A. cannot divide by zero

B. 0

C. 10

D. runtime error

Solution

1. Step 1: Analyze the divide function call

   divide(10, 0) checks if b is zero, which it is, so it returns an error with message "cannot divide by zero".

2. Step 2: Check main function error handling

   Since err is not nil, the program prints the error message instead of the result.

3. Final Answer:

   cannot divide by zero -> Option A

4. Quick Check:

   Error message printed when dividing by zero [OK]

Hint: Error returned when dividing by zero prints message [OK]

Common Mistakes:

• Expecting 0 as output instead of error message
• Ignoring error and printing result
• Assuming runtime panic occurs

4. Identify the error in this Go code snippet related to error handling:

package main
import "fmt"
func openFile(name string) error {
  // pretend to open file
  return nil
}
func main() {
  err := openFile("data.txt")
  if err == nil {
    fmt.Println("Error opening file")
  } else {
    fmt.Println("File opened successfully")
  }
}

medium

A. The variable err is not declared properly.

B. The function openFile should return a string, not error.

C. The error check condition is reversed; it should be 'if err != nil'.

D. The fmt package is not imported.

Solution

1. Step 1: Review error check logic in main

   The code checks if err == nil to print an error message, which is incorrect logic.

2. Step 2: Correct error check condition

   It should check if err != nil to detect an error and print the error message.

3. Final Answer:

   The error check condition is reversed; it should be 'if err != nil'. -> Option C

4. Quick Check:

   Error check must be '!= nil' to catch errors [OK]

Hint: Error means err != nil, not err == nil [OK]

Common Mistakes:

• Checking err == nil to detect errors
• Confusing error return types
• Ignoring error handling completely

5. You want to read a file and print its contents in Go. Why should you handle errors returned by the file reading function?

hard

A. Because the file might not exist or be unreadable, causing the program to fail without error handling.

B. Because handling errors makes the file read faster.

C. Because Go requires all functions to return errors even if they never happen.

D. Because error handling automatically fixes missing files.

Solution

1. Step 1: Understand file reading risks

   Files may not exist, be locked, or have permission issues, causing errors when reading.

2. Step 2: Importance of error handling

   Handling errors lets the program respond gracefully instead of crashing or producing wrong output.

3. Final Answer:

   Because the file might not exist or be unreadable, causing the program to fail without error handling. -> Option A

4. Quick Check:

   Handle file errors to avoid crashes [OK]

Hint: Always check file read errors to avoid crashes [OK]

Common Mistakes:

• Assuming files always exist and are readable
• Thinking error handling speeds up file reading
• Believing error handling fixes missing files automatically