Basic input concepts in Go - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this Go program reading input?

Consider this Go program that reads a single word from the user and prints it back:

package main

import (
	"bufio"
	"fmt"
	"os"
)

func main() {
	reader := bufio.NewReader(os.Stdin)
	input, _ := reader.ReadString('\n')
	fmt.Print(input)
}

If the user types hello and presses Enter, what will be printed?

Go

package main

import (
	"bufio"
	"fmt"
	"os"
)

func main() {
	reader := bufio.NewReader(os.Stdin)
	input, _ := reader.ReadString('\n')
	fmt.Print(input)
}

A hello\r\n

B hello

C hello\n

D Error: input not read

💡 Hint

Think about what ReadString('\n') includes in the returned string.

The ReadString('\n') method reads input until it finds a newline character, and includes that newline in the returned string. So the output will be hello\n.

❓ Predict Output

intermediate

What happens if you use fmt.Scanln to read input?

Look at this Go code snippet:

package main

import "fmt"

func main() {
	var name string
	fmt.Print("Enter your name: ")
	fmt.Scanln(&name)
	fmt.Println("Hello,", name)
}

If the user types John Doe and presses Enter, what will be printed?

Go

package main

import "fmt"

func main() {
	var name string
	fmt.Print("Enter your name: ")
	fmt.Scanln(&name)
	fmt.Println("Hello,", name)
}

A Hello, John Doe

B Hello, John

C Hello,

D Runtime error

💡 Hint

Remember how Scanln reads input and stops at spaces.

fmt.Scanln reads input until the first space or newline. So it reads only "John" and stops before "Doe". The output is "Hello, John".

❓ Predict Output

advanced

What is the output when reading multiple values with fmt.Scan?

Consider this Go program:

package main

import "fmt"

func main() {
	var a, b int
	fmt.Print("Enter two numbers: ")
	fmt.Scan(&a, &b)
	fmt.Println(a + b)
}

If the user inputs 3 5 and presses Enter, what will be printed?

Go

package main

import "fmt"

func main() {
	var a, b int
	fmt.Print("Enter two numbers: ")
	fmt.Scan(&a, &b)
	fmt.Println(a + b)
}

A 8

B 35

C 0

D Runtime error

💡 Hint

Think about how fmt.Scan parses multiple inputs separated by spaces.

fmt.Scan reads two integers separated by space and stores them in a and b. Then it prints their sum, which is 8.

❓ Predict Output

advanced

What error occurs when scanning input into wrong variable types?

Look at this Go code:

package main

import "fmt"

func main() {
	var x int
	fmt.Print("Enter a number: ")
	_, err := fmt.Scanf("%d", &x)
	if err != nil {
		fmt.Println("Error:", err)
	} else {
		fmt.Println("You entered", x)
	}
}

If the user types hello and presses Enter, what will be printed?

Go

package main

import "fmt"

func main() {
	var x int
	fmt.Print("Enter a number: ")
	_, err := fmt.Scanf("%d", &x)
	if err != nil {
		fmt.Println("Error:", err)
	} else {
		fmt.Println("You entered", x)
	}
}

A Program crashes

B You entered 0

C Error: expected integer input

D Error: input mismatch

💡 Hint

What happens if you try to scan a string into an integer variable?

fmt.Scanf returns an error if the input cannot be converted to the variable type. Here, scanning "hello" into an int causes an input mismatch error.

🧠 Conceptual

expert

How does bufio.Reader differ from fmt.Scanln for input reading?

Which statement best describes the difference between using bufio.Reader.ReadString('\n') and fmt.Scanln for reading input in Go?

A <code>bufio.Reader.ReadString('\n')</code> reads the entire line including spaces and newline, while <code>fmt.Scanln</code> reads input only up to the first space or newline.

B <code>fmt.Scanln</code> reads the entire line including spaces and newline, while <code>bufio.Reader.ReadString('\n')</code> reads input only up to the first space.

C Both read input until the first space and exclude the newline character.

D <code>bufio.Reader.ReadString('\n')</code> reads input word by word, while <code>fmt.Scanln</code> reads the entire line.

💡 Hint

Think about how each method treats spaces and newlines in input.

bufio.Reader.ReadString('\n') reads the full line including spaces and the newline character. fmt.Scanln reads input until the first space or newline, so it stops early if spaces appear.