Practical use cases in Go

Introduction

Practical use cases show how to use Go in real life to solve common problems simply and clearly.

When you want to build a simple web server to share information.

When you need to read and write files on your computer.

When you want to process data like numbers or text quickly.

When you want to create a small program that talks to a database.

When you want to make a tool that runs commands automatically.

Syntax

Go

// Go programs start with package main
package main

import "fmt"

func main() {
    // Your code here
    fmt.Println("Hello, world!")
}

Every Go program starts with package main and a main function.

Use import to include extra tools like fmt for printing.

Examples

Prints a simple message to the screen.

Go

package main

import "fmt"

func main() {
    fmt.Println("Print a message")
}

Creates a file and writes text into it.

Go

package main

import (
    "fmt"
    "os"
)

func main() {
    file, err := os.Create("test.txt")
    if err != nil {
        fmt.Println("Error creating file")
        return
    }
    defer file.Close()
    file.WriteString("Hello file")
    fmt.Println("File written")
}

Defines a function to add two numbers and prints the result.

Go

package main

import "fmt"

func add(a int, b int) int {
    return a + b
}

func main() {
    sum := add(3, 4)
    fmt.Println("Sum is", sum)
}

Sample Program

This program starts a simple web server on your computer. When you open http://localhost:8080 in a browser, it shows 'Hello, visitor!'.

Go

package main

import (
    "fmt"
    "net/http"
)

func helloHandler(w http.ResponseWriter, r *http.Request) {
    fmt.Fprintln(w, "Hello, visitor!")
}

func main() {
    http.HandleFunc("/", helloHandler)
    fmt.Println("Starting server at :8080")
    err := http.ListenAndServe(":8080", nil)
    if err != nil {
        fmt.Println("Server error:", err)
    }
}

Important Notes

Go is great for building fast and simple tools.

You can combine small programs like these to make bigger projects.

Always check for errors when working with files or network.

Summary

Practical use cases help you see how Go works in real life.

You can build web servers, work with files, and do math easily.

Start small and build your skills step by step.

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