Break statements

If this endless loop will run until it may lead to the program crashing, why would we use it? Such loops are meaningful especially for cases where the program demands to repeat unconditionally until users provide some signal to stop the loop. break statement is used in loops to indicate such stop signals, i.e., in what conditions the loop can be ended regardless of whether the loop exit condition is satisfied.

The form of a while loop with a break statement is as follows.

while True:
    <Statement(s) #1>
    if <Break Condition>:
        break
    <Statement(s) #2>

<Break Condition> can be any boolean expression that represents either True or False. The block of <Statement(s) #1> and <Statement(s) #2> will be implemented repeatedly until <Break Condition> becomes satisfied at some point. Once <Break Condition> is met, the while loop is stopped without executing <Statement(s) #2>. To be specific, the progression of a while loop with a break statement is as follows:

Step 1. Check whether the exit condition of the while loop is True, which is always the case for infinite loops. Continue to Step 2.

Step 2. Execute <Statement(s) #1>.

Step 3. Check if <Break Condition> is True. If so, end the while loop and skip to Step 6. Otherwise, continue to Step 4.

Step 4. Execute <Statements #2>.

Step 5. Go to Step 1.

Step 6. Exit the loop.

Now, we are ready to see an example that uses an infinite while loop with a break statement. Let’s go back to the infinite name-prompt program, with an additional feature that the user can type ‘stop’ to exit the loop. We set this feature with lowercase ‘stop’ so that even if the name of a user happens to be ‘Stop’, the program can tell whether the input is a stop signal or the name of the user.

Here is the result.

Please enter your name: Gerald
You entered Gerald
Please enter your name: Sorin
You entered Sorin
Please enter your name: Yeohee
You entered Yeohee
Please enter your name: Annie
You entered Annie
Please enter your name: Winny
You entered Winny
Please enter your name: stop
Program ended

As expected, the loop keeps taking input and printing the name until you type ‘stop’, which turns the condition of the break statement from False into True.