5.4: Break and Continue

Learning Objectives

By the end of this section you should be able to

• Analyze a loop's execution with break and continue statements.
• Use break and continue control statements in while and for loops.

Break

A break statement is used within a for or a while loop to allow the program execution to exit the loop once a given condition is triggered. A break statement can be used to improve runtime efficiency when further loop execution is not required.

Ex: A loop that looks for the character "a" in a given string called user_string. The loop below is a regular for loop for going through all the characters of user_string. If the character is found, the break statement takes execution out of the for loop. Since the task has been accomplished, the rest of the for loop execution is bypassed.

    user_string = "This is a string."
    for i in range(len(user_string)):
      if user_string[i] == 'a':
        print("Found at index:", i)
        break

Checkpoint: Break statement in a while loop

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Infinite loop

A break statement is an essential part of a loop that does not have a termination condition. A loop without a termination condition is known as an infinite loop. Ex: An infinite loop that counts up starting from 1 and prints the counter's value while the counter's value is less than 10. A break condition is triggered when the counter's value is equal to 10, and hence the program execution exits.

    counter = 1
    while True:
      if counter >= 10:
        break
      print(counter)
      counter += 1

Concepts in Practice: Using a break statement

1.

What is the following code's output?

string_val = "Hello World"
for c in string_val:
  if c == " ":
    break
  print(c)

1. Hello

Hello World

H
e
l
l
o

2.

Given the following code, how many times does the print statement get executed?

i = 1
while True:
  if i%3 == 0 and i%5 == 0:
    print(i)
    break
  i += 1

1. 0
2. 1
3. 15

3.

What is the final value of i?

i = 1
count = 0
while True:
  if i%2 == 0 or i%3 == 0:
    count += 1
  if count >= 5:
    print(i)
    break
  i += 1

1. 5
2. 8
3. 30

Continue

A continue statement allows for skipping the execution of the remainder of the loop without exiting the loop entirely. A continue statement can be used in a for or a while loop. After the continue statement's execution, the loop expression will be evaluated again and the loop will continue from the loop's expression. A continue statement facilitates the loop's control and readability.

Checkpoint: Continue statement in a while loop

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Concepts in Practice: Using a continue statement

4.

Given the following code, how many times does the print statement get executed?

i = 10
while i >= 0:
  i -= 1
  if i%3 != 0:
    continue
  print(i)

1. 3

4

11

5.

What is the following code's output?

for c in "hi Ali":
  if c == " ":
    continue
  print(c)

1. h
   i
   
   A
   l
   i

2. h
   i
   A
   l
   i

3. hi
   Ali

Try It: Using break control statement in a loop

Write a program that reads a string value and prints "Found" if the string contains a space character. Else, prints "Not found".

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Try It: Using a continue statement in a loop

Complete the following code so that the program calculates the sum of all the numbers in list my_list that are greater than or equal to 5.

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