Example (Go) - Bank Packages

// go.mod
module example.com/bank

go 1.22.0

require github.com/Pallinder/go-randomdata v1.2.0

// bank.go
package main

import (
	"fmt"
    "example.com/bank/fileops"
    "github.com/Pallinder/go-randomdata"
)

const accountBalanceFile string = "balance.txt"

func main() {
	accountBalance, err := fileops.GetFloatFromFile(accountBalanceFile)
	if err != nil {
		fmt.Println("Error:", err)
		fmt.Println("Continuing with default balance of $1000.00")
	}

	fmt.Println("Welcome to Go Bank!")
    fmt.Println("Reach us 24/7 at", randomdata.PhoneNumber())

	for {
		fmt.Println("=====================")

		// ====Can call function from the other file since====
		// ====both files belong to same main package====
		presentOption()

		var choice int
		fmt.Print("Select Option: ")
		fmt.Scan(&choice)
		fmt.Println("You Chose: ", choice)

		if choice == 1 {
			fmt.Printf("Your balance is $%.2f\n", accountBalance)
		} else if choice == 2 {
			fmt.Print("Enter amount to deposit: ")
			var depositAmount float64
			fmt.Scan(&depositAmount)

			if depositAmount <= 0 {
				fmt.Println("Invalid amount. Amount must be greater than 0.")
				continue
			}

			accountBalance += depositAmount
			fmt.Printf("Your new balance is $%.2f\n", accountBalance)
			fileops.WriteFloatToFile(accountBalance, accountBalanceFile)
		} else if choice == 3 {
			fmt.Print("Enter amount to withdraw: ")
			var withdrawAmount float64
			fmt.Scan(&withdrawAmount)

			if withdrawAmount <= 0 {
				fmt.Println("Invalid amount. Amount must be greater than 0.")
				continue
			}
			if withdrawAmount > accountBalance {
				fmt.Println("Insufficient funds.")
				continue
			}

			accountBalance -= withdrawAmount
			fmt.Printf("Your new balance is $%.2f\n", accountBalance)
			fileops.WriteFloatToFile(accountBalance, accountBalanceFile)
		} else {
			fmt.Println("Exiting...")
			break
		}
	}
}

// communication.go
package main // Assign to the same package

import "fmt"

func presentOption () {
    fmt.Println("What do you want to do?")
    fmt.Println("1. Check Balance")
    fmt.Println("2. Deposit Money")
    fmt.Println("3. Withdraw Money")
    fmt.Println("4. Exit")
}

// fileops/filerw.go
package fileops

import (
	"errors"
	"fmt"
	"os"
	"strconv"
)

// ====Only variables and functions with capital letters can be exported====
func WriteFloatToFile(float float64, fileName string) {
	var floatText string = fmt.Sprint(float)
	os.WriteFile(fileName, []byte(floatText), 0644) // 0644 = read and write
}

func GetFloatFromFile(fileName string) (float64, error) {
	data, err := os.ReadFile(fileName)
	if err != nil {
		return 1000, errors.New("Failed to find/read file.")
	}

	var floatText string = string(data)
	float, err := strconv.ParseFloat(floatText, 64)
	if err != nil {
		return 1000, errors.New("Failed to parse float.")
	}

	return float, nil