use PrintErrln instead of log

cmd/sqrtRepetend.go

@@ -18,7 +18,6 @@ package cmd
 
 import (
 	"fmt"
-	"log"
 	"math/big"
 
 	"github.com/spf13/cobra"
@@ -31,13 +30,13 @@ func sqrtRepetend(cmd *cobra.Command, args []string) {
 	for _, s := range args {
 		_, ok := x.SetString(s, 10)
 		if !ok {
-			log.Print("invalid input " + s)
+			cmd.PrintErrln("invalid input " + s)
 			continue
 		}
 
 		repetend, err := lib.SqrtRepetend(x)
 		if err != nil {
-			log.Print(s + " is a perfect square")
+			cmd.PrintErrln(s + " is a perfect square")
 			continue
 		}