improve error handling

main.go

@@ -2,15 +2,26 @@ package main
 
 import (
 	"fmt"
+	"log"
 	"os"
 
 	"github.com/learning-go-book/formatter"
 	"github.com/shopspring/decimal"
 )
 
 func main() {
-	amount, _ := decimal.NewFromString(os.Args[1])
-	percent, _ := decimal.NewFromString(os.Args[2])
+	if len(os.Args) < 3 {
+		fmt.Println("Need two parameters: amount and percent")
+		os.Exit(1)
+	}
+	amount, err := decimal.NewFromString(os.Args[1])
+	if err != nil {
+		log.Fatal(err)
+	}
+	percent, err := decimal.NewFromString(os.Args[2])
+	if err != nil {
+		log.Fatal(err)
+	}
 	percent = percent.Div(decimal.NewFromInt(100))
 	total := amount.Add(amount.Mul(percent)).Round(2)
 	fmt.Println(formatter.Space(80, os.Args[1], os.Args[2], total.StringFixed(2)))