added helpful comments

main.go

@@ -12,16 +12,20 @@ import (
 )
 
 func main() {
+	// Set Welcome Header
 	pterm.DefaultHeader.WithBackgroundStyle(pterm.NewStyle(pterm.BgCyan)).WithTextStyle(pterm.NewStyle(pterm.FgCyan)).Println("Welcome to Checkdigit Calculator")
 
+	// Check what directory the commandline is on when the program is launched.
 	directory, err := os.Getwd()
 	Error(err)
 
+	// Get name of file to be processed.
 	pterm.Printf(pterm.Cyan("What is the name of the file in this directory?: "))
 	reader := bufio.NewReader(os.Stdin)
 	input, err := reader.ReadString('\n')
 	Error(err)
 
+	// Create upcs array and push all upc strings into it
 	input = strings.TrimSpace(input)
 	file, err := os.Open(input)
 	Error(err)
@@ -36,12 +40,13 @@ func main() {
 		fmt.Println(scanner.Err())
 	}
 
+	// Start PTerm Spinner
 	pterm.DefaultSpinner.Start()
 
-	Error(err)
-
+	// Create gtins array that will eventually be returned
 	var gtins []string
 
+	// Using regex compile so the program stays fast
 	regex, err := regexp.Compile("[^0-9]")
 	Error(err)
 
@@ -119,23 +124,29 @@ func main() {
 		gtins = append(gtins, upc+remainderString)
 	}
 
+	// Check if answer.txt already exists and if so, delete it
 	if _, err := os.Stat(directory + "/answer.txt"); err == nil {
 		e := os.Remove(directory + "/answer.txt")
 		Error(e)
 	}
 
+	// Create new answer.txt
 	answerFile, err := os.Create(directory + "/answer.txt")
 	Error(err)
 
 	defer answerFile.Close()
 
+	// Fill the answers.txt file
 	for _, gtin := range gtins {
 		_, err := answerFile.WriteString(gtin + "\n")
 		Error(err)
 	}
 
+	// Stop the Spinner
 	pterm.DefaultSpinner.Stop()
 
+	// Print Success message and exit
 	pterm.Printf("\n")
 	pterm.Success.Println("The answer.txt file has been successfully generated with check digits.")
+	os.Exit(0)
 }