use flag for limit

cmd/totient.go

@@ -18,28 +18,29 @@ package cmd
 
 import (
 	"fmt"
-	"strconv"
 
 	"github.com/spf13/cobra"
 )
 
-func totientSieve(n int) chan int {
-	totients := make([]int, n)
+var totientN uint
+
+func totientSieve(n uint) chan uint {
+	totients := make([]uint, n)
 	totients[0] = 0
 	totients[1] = 1
-	for i := 2; i < n; i++ {
+	for i := uint(2); i < n; i++ {
 		totients[i] = i - 1
 	}
 
-	ch := make(chan int)
+	ch := make(chan uint)
 	go func() {
-		for i := 0; i < n; i++ {
+		for i := uint(0); i < n; i++ {
 			ch <- totients[i]
 			if i == 0 || i == 1 || totients[i] != i-1 {
 				continue
 			}
 
-			for j := 2 * i; j < n; j += i {
+			for j := uint(2 * i); j < n; j += i {
 				totients[j] -= totients[j] / i
 			}
 		}
@@ -51,12 +52,7 @@ func totientSieve(n int) chan int {
 }
 
 func totient(cmd *cobra.Command, args []string) {
-	n, err := strconv.Atoi(args[0])
-	if err != nil {
-		cobra.CheckErr(err)
-	}
-
-	for v := range totientSieve(n) {
+	for v := range totientSieve(totientN) {
 		fmt.Println(v)
 	}
 }
@@ -81,4 +77,7 @@ func init() {
 	// Cobra supports local flags which will only run when this command
 	// is called directly, e.g.:
 	// totientCmd.Flags().BoolP("toggle", "t", false, "Help message for toggle")
+
+	totientCmd.Flags().UintVarP(&totientN, "limit", "n", 0, "upper limit")
+	totientCmd.MarkFlagRequired("limit")
 }