Practical use cases in Go - Mini Project: Build & Apply

Practical use cases

📖 Scenario: You are working on a small store inventory system. You want to keep track of products and their prices, then find which products are affordable under a certain budget.

🎯 Goal: Build a Go program that stores product prices, sets a budget limit, filters products affordable within that budget, and prints the affordable products.

📋 What You'll Learn

Create a map called products with product names as keys and prices as float64 values

Create a variable called budget with a float64 value

Use a for loop to find products with prices less than or equal to budget

Store affordable products in a new map called affordable

Print the affordable map

💡 Why This Matters

🌍 Real World

Managing product prices and budgets is common in retail and inventory systems.

💼 Career

Understanding maps, loops, and conditionals in Go is essential for backend and systems programming jobs.

1

Create the products map

Create a map called products with these exact entries: "Apple": 1.20, "Banana": 0.80, "Cherry": 2.50, "Date": 3.00, "Eggplant": 1.50

Go

package main

func main() {
    // Create the products map here
}

Hint

Use a map literal with string keys and float64 values.

2

Set the budget variable

Create a variable called budget with the float64 value 2.00 inside the main function, below the products map.

Go

package main

func main() {
    products := map[string]float64{
        "Apple": 1.20,
        "Banana": 0.80,
        "Cherry": 2.50,
        "Date": 3.00,
        "Eggplant": 1.50,
    }
    // Create the budget variable here
}

Hint

Use a simple variable declaration with := and a float64 value.

3

Filter affordable products

Create a new map called affordable of type map[string]float64. Use a for loop with variables product and price to iterate over products. Inside the loop, add products with price less than or equal to budget to the affordable map.

Go

package main

func main() {
    products := map[string]float64{
        "Apple": 1.20,
        "Banana": 0.80,
        "Cherry": 2.50,
        "Date": 3.00,
        "Eggplant": 1.50,
    }
    budget := 2.00
    // Create affordable map and filter products here
}

Hint

Use make to create the map, then a for loop with range to iterate.

4

Print the affordable products

Use fmt.Println to print the affordable map. Remember to import the fmt package at the top.

Go

package main

import "fmt"

func main() {
    products := map[string]float64{
        "Apple": 1.20,
        "Banana": 0.80,
        "Cherry": 2.50,
        "Date": 3.00,
        "Eggplant": 1.50,
    }
    budget := 2.00
    affordable := make(map[string]float64)
    for product, price := range products {
        if price <= budget {
            affordable[product] = price
        }
    }
    // Print the affordable map here
}

Hint

Use fmt.Println(affordable) to print the map.

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