Practical use cases in Go - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to print "Hello, World!" in Go.

Go

package main

import "fmt"

func main() {
    fmt.[1]("Hello, World!")
}

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

APrint

BPrintf

CPrintln

DPrintfln

Attempts:

3 left

💡 Hint

Common Mistakes

Using Print instead of Println, which does not add a new line.

Using a non-existent function like Printfln.

The Println function prints the text followed by a new line.

2fill in blank

medium

Complete the code to declare a variable named "count" of type int with value 10.

Go

package main

func main() {
    var count [1] = 10
}

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

Aint

Bstring

Cfloat64

Dbool

Attempts:

3 left

💡 Hint

Common Mistakes

Using string type for a number.

Using float64 when an integer is intended.

The variable count is declared as an integer using int type.

3fill in blank

hard

Fix the error in the code to correctly create a slice of strings named "fruits".

Go

package main

func main() {
    fruits := [1]{"apple", "banana", "cherry"}
}

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

A[]string

Bmap

Cslice

Darray

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'array' or 'slice' as a type name, which are not valid Go types.

Using 'map' which is a key-value structure.

In Go, a slice of strings is declared as []string.

4fill in blank

hard

Fill both blanks to create a map from string to int and add a key-value pair.

Go

package main

func main() {
    ages := make(map[string][1])
    ages["Alice"] = [2]
}

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

Aint

B25

Cstring

D30

Attempts:

3 left

💡 Hint

Common Mistakes

Using string as the map value type but assigning an integer.

Assigning a string value instead of an integer.

The map stores integers as values, so the type is int. The value assigned to "Alice" is 25.

5fill in blank

hard

Fill all three blanks to define a function that returns the sum of two integers.

Go

package main

func [1](a [2], b [2]) [3] {
    return a + b
}

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

Aadd

Bint

Dsum

Attempts:

3 left

💡 Hint

Common Mistakes

Using different types for parameters and return value.

Using a function name that does not match the operation.

The function is named add, takes two integers, and returns an integer.

Practice

1. Which Go feature is commonly used to create a simple web server that listens on a port?

easy

A. The net/http package with http.ListenAndServe

B. The fmt package with Println

C. The os package with Open

D. The math package with Pow

Solution

1. Step 1: Identify the package for web servers

   The net/http package provides tools to create web servers in Go.

2. Step 2: Recognize the function to start the server

   http.ListenAndServe starts a server listening on a specified port.

3. Final Answer:

   The net/http package with http.ListenAndServe -> Option A

4. Quick Check:

   Web server = net/http.ListenAndServe [OK]

Hint: Web servers use net/http.ListenAndServe to listen on ports [OK]

Common Mistakes:

• Confusing printing functions with server functions
• Using file operations instead of network functions
• Thinking math package handles networking

2. Which of the following is the correct syntax to open a file named "data.txt" for reading in Go?

easy

A. file, err := os.Open("data.txt")

B. file := os.OpenFile("data.txt", os.O_WRONLY)

C. file, err := ioutil.ReadFile("data.txt")

D. file := os.Read("data.txt")

Solution

1. Step 1: Identify the function to open a file for reading

   os.Open opens a file in read-only mode and returns a file and error.

2. Step 2: Check the syntax correctness

   The syntax file, err := os.Open("data.txt") correctly assigns both file and error.

3. Final Answer:

   file, err := os.Open("data.txt") -> Option A

4. Quick Check:

   Open file for reading = os.Open [OK]

Hint: Use os.Open with two variables to open files safely [OK]

Common Mistakes:

• Using os.Read which does not exist
• Using ioutil.ReadFile which reads whole file, not opens
• Opening file with wrong flags for reading

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

package main
import "fmt"
func main() {
    nums := []int{2, 4, 6}
    squares := make(map[int]int)
    for _, n := range nums {
        squares[n] = n * n
    }
    fmt.Println(squares)
}

medium

A. map[2:4 4:8 6:12]

B. map[2:4 4:16 6:36]

C. map[2:8 4:16 6:36]

D. map[2:2 4:4 6:6]

Solution

1. Step 1: Understand the loop and map assignment

   The loop goes through each number in nums and assigns squares[n] = n * n.

2. Step 2: Calculate each square value

   2*2=4, 4*4=16, 6*6=36, so the map stores these pairs.

3. Final Answer:

   map[2:4 4:16 6:36] -> Option B

4. Quick Check:

   Squares map = map with keys and squared values [OK]

Hint: Map keys with squares store n:n*n pairs [OK]

Common Mistakes:

• Confusing keys and values in map
• Multiplying incorrectly
• Expecting slice output instead of map

4. This Go code tries to read a file but has an error. What is the problem?

package main
import (
    "fmt"
    "os"
)
func main() {
    file := os.Open("file.txt")
    defer file.Close()
    fmt.Println("File opened")
}

medium

A. File name should be absolute path

B. Using defer incorrectly

C. Missing error check after os.Open

D. fmt.Println cannot print strings

Solution

1. Step 1: Check os.Open usage

   os.Open returns two values: file and error. The code only assigns one variable.

2. Step 2: Identify missing error handling

   Without checking error, the program may panic if file does not open.

3. Final Answer:

   Missing error check after os.Open -> Option C

4. Quick Check:

   Always check error from os.Open [OK]

Hint: Always assign and check error from os.Open [OK]

Common Mistakes:

• Ignoring error returned by os.Open
• Assuming defer is wrong here
• Thinking file path must be absolute always

5. You want to create a Go program that reads a list of numbers from a file, squares each number, and writes the results to a new file. Which approach best combines Go features for this task?

hard

A. Use fmt.Println to read and write files directly

B. Use net/http to read files and fmt.Scan to write

C. Use math.Pow to read files and os.Remove to write

D. Use os.Open to read, loop to square, and os.Create with WriteString to save

Solution

1. Step 1: Reading numbers from a file

   os.Open opens the file for reading; then you can scan or read lines.

2. Step 2: Processing and writing results

   Loop through numbers, square them, then use os.Create to create output file and WriteString or similar to write results.

3. Final Answer:

   Use os.Open to read, loop to square, and os.Create with WriteString to save -> Option D

4. Quick Check:

   File read + process + write = os.Open + loop + os.Create [OK]

Hint: Read with os.Open, write with os.Create, process in loop [OK]

Common Mistakes:

• Using fmt.Println for file I/O
• Confusing math.Pow with file reading
• Using network packages for file tasks