Sending and receiving values in Go - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this Go code using channels?

Consider the following Go program. What will it print when run?

Go

package main
import "fmt"
func main() {
    ch := make(chan int)
    go func() {
        ch <- 42
    }()
    val := <-ch
    fmt.Println(val)
}

A Deadlock error

B 0

C Compilation error

D 42

💡 Hint

Think about how the goroutine sends a value and the main goroutine receives it.

The anonymous goroutine sends 42 into the channel ch. The main goroutine receives it and prints 42.

❓ Predict Output

intermediate

What happens if you try to receive from a closed channel?

What will this Go program print?

Go

package main
import "fmt"
func main() {
    ch := make(chan int, 1)
    ch <- 10
    close(ch)
    val1, ok1 := <-ch
    val2, ok2 := <-ch
    fmt.Println(val1, ok1)
    fmt.Println(val2, ok2)
}

A

10 true
0 false

B

10 true
10 true

C

0 false
0 false

D Compilation error

💡 Hint

Remember what happens when you receive from a closed channel with buffered values.

The first receive gets the buffered value 10 and ok is true. The second receive gets zero value 0 and ok is false because channel is closed and empty.

🔧 Debug

advanced

Why does this Go program deadlock?

Examine the code below. Why does it cause a deadlock?

Go

package main
func main() {
    ch := make(chan int)
    ch <- 5
    val := <-ch
    println(val)
}

A Because the channel is buffered and full

B Because the send operation blocks forever since no goroutine is receiving

C Because the channel is closed before sending

D Because the receive operation blocks forever since no value is sent

💡 Hint

Think about how unbuffered channels block on send and receive.

The send operation blocks because no goroutine is ready to receive from the unbuffered channel, causing deadlock.

🧠 Conceptual

advanced

What is the effect of closing a channel in Go?

Which statement about closing a channel is true?

A Closing a channel allows receivers to detect no more values will be sent

B Closing a channel prevents any further values from being received

C Closing a channel automatically empties all buffered values

D Closing a channel causes a runtime panic if any goroutine is receiving

💡 Hint

Think about how receivers can check if a channel is closed.

Closing a channel signals receivers that no more values will come, allowing them to stop receiving gracefully.

❓ Predict Output

expert

What is the output of this Go program with multiple goroutines and channels?

Analyze the code and select the correct output.

Go

package main
import (
    "fmt"
    "sync"
)
func main() {
    ch := make(chan int)
    var wg sync.WaitGroup
    wg.Add(2)
    go func() {
        defer wg.Done()
        for i := 0; i < 3; i++ {
            ch <- i
        }
    }()
    go func() {
        defer wg.Done()
        for i := 3; i < 6; i++ {
            ch <- i
        }
    }()
    go func() {
        wg.Wait()
        close(ch)
    }()
    sum := 0
    for v := range ch {
        sum += v
    }
    fmt.Println(sum)
}

A Compilation error

B 21

C 15

D Deadlock error

💡 Hint

Consider the values sent on the channel and how the sum is calculated.

The two goroutines send values 0 to 2 and 3 to 5, total sum is 0+1+2+3+4+5=15.