Program stability concepts in Go - Mini Project: Build & Apply

Program Stability Concepts in Go

📖 Scenario: You are building a simple Go program that processes a list of tasks with their durations. You want to make sure the program handles unexpected situations gracefully to stay stable.

🎯 Goal: Build a Go program that creates a map of tasks and durations, sets a maximum allowed duration, filters tasks that exceed this duration, and prints the filtered tasks. This teaches how to keep a program stable by controlling input and output.

📋 What You'll Learn

Create a map called tasks with exact entries: "Email": 30, "Meeting": 90, "Coding": 120, "Break": 15

Create an integer variable called maxDuration and set it to 60

Use a for loop with variables task and duration to iterate over tasks and create a new map filteredTasks with only tasks having duration less than or equal to maxDuration

Print the filteredTasks map

💡 Why This Matters

🌍 Real World

Filtering tasks by duration helps keep programs stable by avoiding processing tasks that take too long.

💼 Career

Understanding how to filter and control data flow is important for writing reliable and maintainable Go programs in software development.

1

Create the initial tasks map

Create a map called tasks with these exact entries: "Email": 30, "Meeting": 90, "Coding": 120, "Break": 15

Go

# Create the tasks map with exact entries
# Your code here

Hint

Use map[string]int to create a map with string keys and int values.

2

Set the maximum allowed duration

Create an integer variable called maxDuration and set it to 60

Go

package main

func main() {
    tasks := map[string]int{"Email": 30, "Meeting": 90, "Coding": 120, "Break": 15}
    // Create maxDuration variable and set to 60
    // Your code here
}

Hint

Use := to declare and assign maxDuration in one step.

3

Filter tasks by duration

Use a for loop with variables task and duration to iterate over tasks and create a new map called filteredTasks with only tasks having duration less than or equal to maxDuration

Go

package main

func main() {
    tasks := map[string]int{"Email": 30, "Meeting": 90, "Coding": 120, "Break": 15}
    maxDuration := 60
    // Create filteredTasks map
    // Use for loop to add tasks with duration <= maxDuration
    // Your code here
}

Hint

Use make(map[string]int) to create an empty map. Use for task, duration := range tasks to loop.

4

Print the filtered tasks

Write fmt.Println(filteredTasks) to print the filteredTasks map

Go

package main

import "fmt"

func main() {
    tasks := map[string]int{"Email": 30, "Meeting": 90, "Coding": 120, "Break": 15}
    maxDuration := 60
    filteredTasks := make(map[string]int)
    for task, duration := range tasks {
        if duration <= maxDuration {
            filteredTasks[task] = duration
        }
    }
    // Print filteredTasks map
    // Your code here
}

Hint

Use fmt.Println to print the map. The output should show only tasks with duration 60 or less.

Practice

1. What is the main purpose of using recover() in Go programs?

easy

A. To declare a new variable

B. To start a new goroutine

C. To catch a panic and prevent the program from crashing

D. To handle normal errors returned by functions

Solution

1. Step 1: Understand panic and recover

   Panic causes a program to stop running immediately unless recovered.

2. Step 2: Role of recover()

   Recover is used inside a deferred function to catch the panic and allow the program to continue.

3. Final Answer:

   To catch a panic and prevent the program from crashing -> Option C

4. Quick Check:

   recover() catches panic = C [OK]

Hint: recover() only works inside deferred functions [OK]

Common Mistakes:

• Thinking recover() handles normal errors
• Using recover() outside defer
• Confusing recover() with panic()

2. Which of the following is the correct syntax to defer a function call in Go?

easy

A. defer fmt.Println("Hello")

B. defer = fmt.Println("Hello")

C. defer: fmt.Println("Hello")

D. defer -> fmt.Println("Hello")

Solution

1. Step 1: Recall defer syntax

   In Go, defer is a keyword placed before a function call to delay its execution.

2. Step 2: Check each option

   Only defer fmt.Println("Hello") uses 'defer' correctly before the function call without extra symbols.

3. Final Answer:

   defer fmt.Println("Hello") -> Option A

4. Quick Check:

   defer + function call = D [OK]

Hint: defer must be followed directly by a function call [OK]

Common Mistakes:

• Adding '=' after defer
• Using ':' or '->' after defer
• Not calling a function after defer

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

package main
import "fmt"
func main() {
    defer func() {
        if r := recover(); r != nil {
            fmt.Println("Recovered from panic:", r)
        }
    }()
    fmt.Println("Start")
    panic("Something went wrong")
    fmt.Println("End")
}

medium

A. Start
panic: Something went wrong

B. Start
End
Recovered from panic: Something went wrong

C. Start
End

D. Start
Recovered from panic: Something went wrong

Solution

1. Step 1: Trace program execution

   "Start" is printed first. Then panic is called, which triggers the deferred function.

2. Step 2: Deferred function recovers panic

   The deferred anonymous function calls recover(), catches the panic, and prints the recovery message. Execution does not continue after panic call, so "End" is not printed.

3. Final Answer:

   Start Recovered from panic: Something went wrong -> Option D

4. Quick Check:

   panic caught by recover = A [OK]

Hint: Deferred recover runs on panic, then execution continues after panic [OK]

Common Mistakes:

• Thinking code after panic does not run
• Missing recover() inside defer
• Confusing panic message with normal print

4. Identify the error in this Go code that tries to recover from a panic:

package main
import "fmt"
func main() {
    if r := recover(); r != nil {
        fmt.Println("Recovered:", r)
    }
    panic("Oops")
}

medium

A. recover() must be called inside a deferred function

B. panic() must be called before recover()

C. recover() cannot be used with panic()

D. fmt.Println() cannot be used inside if statement

Solution

1. Step 1: Understand recover usage

   recover() only works if called inside a deferred function; here it is called directly in main.

2. Step 2: Analyze code flow

   Since recover() is not deferred, it cannot catch the panic, so the program will crash.

3. Final Answer:

   recover() must be called inside a deferred function -> Option A

4. Quick Check:

   recover inside defer = B [OK]

Hint: Always call recover() inside defer to catch panics [OK]

Common Mistakes:

• Calling recover() directly without defer
• Thinking recover() catches errors, not panics
• Placing panic before recover without defer

5. You want to write a stable Go program that logs a message when a panic occurs but continues running. Which code snippet correctly implements this behavior?

hard

A. func main() {
if r := recover(); r != nil {
fmt.Println("Panic caught:", r)
}
panic("Crash")
fmt.Println("Program continues")
}

B. func main() {
defer func() {
if r := recover(); r != nil {
fmt.Println("Panic caught:", r)
}
}()
panic("Crash")
fmt.Println("Program continues")
}

C. func main() {
panic("Crash")
defer func() {
if r := recover(); r != nil {
fmt.Println("Panic caught:", r)
}
}()
fmt.Println("Program continues")
}

D. func main() {
defer fmt.Println("Program continues")
panic("Crash")
}

Solution

1. Step 1: Check defer and recover placement

   func main() { defer func() { if r := recover(); r != nil { fmt.Println("Panic caught:", r) } }() panic("Crash") fmt.Println("Program continues") } correctly defers a function that calls recover() to catch panic and print a message.

2. Step 2: Verify program flow

   After panic, deferred recover runs, preventing crash and allowing program to continue, executing code after panic.

3. Final Answer:

   Uses defer func() with recover() before panic("Crash") -> Option B

4. Quick Check:

   defer + recover to catch panic = A [OK]

Hint: Defer recover before panic to handle it safely [OK]

Common Mistakes:

• Calling recover() outside defer
• Placing defer after panic
• Not handling panic at all