Buffered and unbuffered channels in Go - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of unbuffered channel communication

What is the output of this Go program using an unbuffered channel?

Go

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

A 42

B deadlock

C 0

D compile error

💡 Hint

Think about how unbuffered channels block until both sender and receiver are ready.

The unbuffered channel blocks the goroutine sending 42 until the main goroutine receives it. So the program prints 42.

❓ Predict Output

intermediate

Output of buffered channel with multiple sends

What will this Go program print?

Go

package main
import (
	"fmt"
)
func main() {
	ch := make(chan int, 2)
	ch <- 10
	ch <- 20
	fmt.Println(<-ch)
	fmt.Println(<-ch)
}

A 20\n10

B 10\n20

C deadlock

D compile error

💡 Hint

Buffered channels allow sending without immediate receiving until full.

The buffered channel holds two values. The first receive gets 10, the second gets 20.

❓ Predict Output

advanced

Deadlock detection with unbuffered channel

What happens when this Go program runs?

Go

package main
func main() {
	ch := make(chan int)
	ch <- 1
	<-ch
}

A compile error

B prints 1

C compiles but no output

D deadlock runtime panic

💡 Hint

Consider that sending on an unbuffered channel blocks until a receiver is ready.

The send blocks forever because no goroutine is receiving yet, causing a deadlock panic.

❓ Predict Output

advanced

Channel capacity and length after sends

What will be the output of this Go program?

Go

package main
import (
	"fmt"
)
func main() {
	ch := make(chan int, 3)
	ch <- 5
	ch <- 10
	fmt.Println(len(ch), cap(ch))
}

A 2 3

B 3 3

C 0 3

D compile error

💡 Hint

len returns the number of elements in the channel buffer, cap returns its capacity.

Two values are sent, so len is 2. Capacity was set to 3.

🧠 Conceptual

expert

Behavior difference between buffered and unbuffered channels

Which statement correctly describes the difference between buffered and unbuffered channels in Go?

A Unbuffered channels store multiple values internally; buffered channels store only one value.

B Buffered channels always block the sender until the receiver receives; unbuffered channels never block.

C Unbuffered channels block the sender until the receiver receives; buffered channels allow sending without blocking until the buffer is full.

D Buffered channels do not support concurrent access; unbuffered channels do.

💡 Hint

Think about how sending and receiving synchronize in each channel type.

Unbuffered channels require sender and receiver to be ready simultaneously, causing blocking. Buffered channels allow sending up to their capacity without blocking.