Why does fmt.Scan() behave in a weird way?

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 main

import "fmt"

func main() {

	var remainingTickets uint = 50
	var userTickets uint

	fmt.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)

}

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 main

import (
	"fmt"
	"strconv"
)

func main() {

	var remainingTickets uint64 = 50
	
	fmt.Print("Enter the number of tickets you want to purchase: ")

	for {
		var userTickets string
		fmt.Scanln(&userTickets)

		// parse to make sure we get a positive (unsigned) integer
		u64, err := strconv.ParseUint(userTickets,10,64)
		// make sure it's a postive integer and not equal to zero
		if 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 left
		if u64 > remainingTickets {
			fmt.Printf("We only have %v tickets available!\n", remainingTickets)
			fmt.Print("Try again! Enter the number of tickets: ")
			continue
		}

		// update remaining tickets
		remainingTickets -= u64
		break
	}

	fmt.Printf("Remaining tickets: %d\n", remainingTickets)
}