英文:
Why does fmt.Scan() behave in a weird way?
问题
我正在尝试验证用户输入。如果用户输入一个整数，它会按预期工作。然而，如果用户输入一个非整数的字符串，变量userTickets会被赋值为0，但会打印出多次Try again! It must be more than zero: 。确切地说，它会打印len(input)次，我不明白为什么会这样。
我还尝试使用fmt.Scanf("%d", &usertickets)来实现期望的结果，但得到了相同的结果。
为什么会出现这种行为，我该如何编写一个解决方法？
package mainimport "fmt"func main() {var remainingTickets uint = 50var userTickets uintfmt.Print("Enter the number of tickets you want to purchase: ")fmt.Scan(&userTickets)for userTickets > remainingTickets {fmt.Printf("We only have %v tickets available!\n", remainingTickets)fmt.Print("Try again! Enter the number of tickets: ")fmt.Scan(&userTickets)}for userTickets == 0 {fmt.Print("Try again! It must be more than zero: ")fmt.Scan(&userTickets)}fmt.Printf("Remaining tickets: %v\n", remainingTickets-userTickets)}
英文:
I'm trying to validate the user input. If the user inputs an integer number it works like expected. However, if the user inputs a non-integer string, the variable userTickets gets assigned value 0, but prints Try again! It must be more than zero: many times. To be exact, it prints len(input) times and I don't understand why.
Also tried achieving desired result using fmt.Scanf("%d", &usertickets) but got an identical result.
Why does it behave this way and how can I write a workaround for it?
package mainimport "fmt"func main() {var remainingTickets uint = 50var userTickets uintfmt.Print("Enter the number of tickets you want to purchase: ")fmt.Scan(&userTickets)for userTickets > remainingTickets {fmt.Printf("We only have %v tickets available!\n", remainingTickets)fmt.Print("Try again! Enter the number of tickets: ")fmt.Scan(&userTickets)}for userTickets == 0 {fmt.Print("Try again! It must be more than zero: ")fmt.Scan(&userTickets)}fmt.Printf("Remaining tickets: %v\n", remainingTickets-userTickets)}
答案1
得分: 1
Scan能够在不读取stdin的全部内容的情况下确定输入不是数字。这就是为什么当输入非数字时，验证逻辑会循环len(input)次的原因。虽然你也可以使用Scanner（人们确实推荐这种方法），但下面是一个类似于你的方法的实现。请注意，所有的验证检查都在一个单独的"for"循环中完成：
package mainimport ("fmt""strconv")func main() {var remainingTickets uint64 = 50fmt.Print("请输入您想购买的票数：")for {var userTickets stringfmt.Scanln(&userTickets)// 解析以确保我们得到一个正（无符号）整数u64, err := strconv.ParseUint(userTickets,10,64)// 确保它是一个正整数且不等于零if err != nil || u64==0{fmt.Print("请重试！您必须输入一个大于零的数字：")continue}// 检查剩余票数是否足够if u64 > remainingTickets {fmt.Printf("我们只剩下 %v 张票！\n", remainingTickets)fmt.Print("请重试！请输入票数：")continue}// 更新剩余票数remainingTickets -= u64break}fmt.Printf("剩余票数：%d\n", remainingTickets)}
希望对你有帮助！
英文:
Scan is able to determine that the input isn't numeric without reading the entire contents of stdin. This is why you validation logic loops for len(input) when non-numeric. While you can use a Scanner as well (and people do recommend that approach), below is an approach similar to yours. Note that all validation checking is done within a single "for" loop as well:
package mainimport ("fmt""strconv")func main() {var remainingTickets uint64 = 50fmt.Print("Enter the number of tickets you want to purchase: ")for {var userTickets stringfmt.Scanln(&userTickets)// parse to make sure we get a positive (unsigned) integeru64, err := strconv.ParseUint(userTickets,10,64)// make sure it's a postive integer and not equal to zeroif err != nil || u64==0{fmt.Print("Try again! You must enter a number greater than zero: ")continue}// check to make sure we have enough tickets leftif u64 > remainingTickets {fmt.Printf("We only have %v tickets available!\n", remainingTickets)fmt.Print("Try again! Enter the number of tickets: ")continue}// update remaining ticketsremainingTickets -= u64break}fmt.Printf("Remaining tickets: %d\n", remainingTickets)}
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