如果输入负数，则停止 while 循环

Question

I've started with learning Python and now I am stuck with the WHILE loop, so if you could give me some advice, I would appreciate it.

So, this is my code and what I need is to stop the whole code if I enter the negative number and to print ("Wrong entry"), but my code, on entering the negative number, still passes and prints me also ("Avg price:"). I would like not to print ("Avg price is: ") when I enter eg (2,3,6, -12) - only to print ("Wrong entry"). I now that my last print is within WHILE loop, but I am trying to find the solutions :) Probably, there is easier solution for this, but as I said I am the newbie and still learning Thank you in advance.

price= int(input("Enter the price: "))

price_list=[]

while price!= 0:
    price_list.append(price)
    if price< 0:
       print("Wrong entry")
       break
    price=int(input())

    price_sum= sum(price_list)
print(f"Avg price is: {price_sum / len(price_list)}")

Answer 1

Using a while/else loop produces your desired behaviour.

• The code in the else doesn't run if the break in the while loop is encountered

Code

price= int(input("Enter the price: "))

price_list=[]

while price!= 0:
    price_list.append(price)
    if price< 0:
       print("Wrong entry")
       break
    price=int(input())

    price_sum= sum(price_list)
else:
    print(f"Avg price is: {price_sum / len(price_list)}")

Answer 2

It's because it is outside the loop, it will always run.

So try this:

price= int(input("Enter the price: "))

price_list=[]

while price != 0:
    if price< 0:
       print("Wrong entry")
       break
    price_list.append(price)
    price=int(input())            
    price_sum= sum(price_list)
if price > 0:
    print(f"Avg price is: {price_sum / len(price_list)}")

Answer 3

If you don't want to run rest of code when getting negative number, you can do something like this:

price= int(input("Enter the price: "))
ok = True
price_list=[]

while price!= 0:
    price_list.append(price)
    if price< 0:
       print("Wrong entry")
       ok = False
       break
    price=int(input())
if ok:
    price_sum= sum(price_list)
    print(f"Avg price is: {price_sum / len(price_list)}")

Answer 4

You have two options here. You can include the check in the while guard, like this while price > 0 or you can use the keyword break and add an if guard inside the loop, like this

if price < 0:
    break

Since the first time you input the price it is outside the loop, the best course would be to add the guard to the while loop, so that it gets skipped in case first input is negative.

Answer 5

You are doing procedural programming here. You print statement it outside the loop. Also, there is no control statement checking the statement. So regardless of the input, print statement is executed.

Since any non empty list is a truth value, you can check if the list is empty or it contains some elements

price= int(input("Enter the price: "))

price_list=[]

while price!= 0:
    
    if price< 0:
       print("Wrong entry")
       break
    price_list.append(price)
    price=int(input())
if price_list:
    price_sum= sum(price_list)
    print(f"Avg price is: {price_sum / len(price_list)}")