break and continue

In Python, loops are a fundamental part of controlling the flow of a program. They allow for repeated execution of a block of code. Two important control keywords that can be used within loops are break and continue. These keywords provide additional control by allowing us to prematurely exit a loop or skip specific iterations. This tutorial provides a detailed examination of these keywords and their use cases.

The break Statement

The break statement is used to exit a loop immediately, regardless of the loop’s condition. This can be particularly useful when a specific condition is met, and there is no need to continue iterating. Here is an example using a while loop:

number = 5

while number > 0:
    number -= 1
    if number == 2:
        print("Breaking at 2")
        break
    print(number)
print("Done")

Explanation:

1. number is initialized to 5.
2. The while loop continues as long as number is greater than 0.
3. Within the loop, number is decremented by 1 in each iteration.
4. If number equals 2, the break statement is executed, exiting the loop immediately.
5. The current value of number is printed if the loop does not break.
6. After the loop exits, "Done" is printed.

Without the break statement, the loop would continue until number reaches 0, printing all values from 4 to 0. With break, the loop exits as soon as number becomes 2.

The continue Statement

The continue statement skips the rest of the code inside the loop for the current iteration and jumps back to the start of the loop for the next iteration. Here’s how it works in a while loop:

number = 5

while number > 0:
    number -= 1
    if number == 2:
        print("Skipping 2")
        continue
    print(number)
print("Done")

Explanation:

1. number is initialized to 5.
2. The while loop continues as long as number is greater than 0.
3. Within the loop, number is decremented by 1 in each iteration.
4. If number equals 2, the continue statement is executed, skipping the rest of the code in the loop for that iteration.
5. The current value of number is printed unless continue is executed.
6. After the loop exits, "Done" is printed.

With continue, when number is 2, the loop skips printing the number and immediately proceeds to the next iteration.

Practical Example: A Simple Calculator

Let’s implement a practical example that incorporates both break and continue statements. We will create a simple calculator that adds positive numbers and exits when the user inputs zero.

total = 0

print("Welcome to Calc Plus")
print("Add positive numbers or insert zero to exit.")

while True:
    user_input = int(input("Enter a number: "))
  
    if user_input < 0:
        print("Please enter positive numbers only.")
        continue
  
    if user_input == 0:
        print(f"Total is {total}")
        break
  
    total += user_input

Explanation:

1. total is initialized to 0 to keep track of the sum.
2. Instructions are printed to guide the user.
3. An infinite while loop is created using while True.
4. The user is prompted to enter a number, which is converted to an integer.
5. If the user inputs a negative number, a warning message is displayed, and the continue statement skips to the next iteration without adding the number to the total.
6. If the user inputs zero, the total sum is printed, and the loop exits with the break statement.
7. If a positive number is inputted, it is added to the total.

This example demonstrates the use of break to exit the loop when the user inputs zero and continue to skip processing when the user inputs a negative number.

Using break and continue in for Loops

The break and continue statements can be used similarly within for loops. Here’s an example:

for number in range(5, 0, -1):
    if number == 2:
        print("Skipping 2")
        continue
    if number == 1:
        print("Breaking at 1")
        break
    print(number)
print("Done")

Explanation:

1. The for loop iterates over a range of numbers from 5 to 1.
2. If number is 2, continue skips the print statement for that iteration.
3. If number is 1, break exits the loop.
4. All other values of number are printed.
5. "Done" is printed after the loop exits.

In summary, break and continue provide powerful control mechanisms within loops, allowing for early exit or skipping iterations based on specific conditions. Understanding these keywords enhances the ability to write efficient and effective Python code.