IG Math Space

By the end of this class session, students will be able to:

• Understand the purpose of control statements in loops.
• Use break to exit a loop immediately.
• Use continue to skip the current iteration and move to the next.
• Use pass as a placeholder in an otherwise-empty block.
• Differentiate clearly between break, continue and pass.
• Apply the correct control statement in search, filtering and menu-driven programs.
• Recognize the effect of break inside nested loops and the loop else clause.

By default, a loop runs from start to finish, executing every iteration. But sometimes we need to alter this normal flow — stop early, skip a step, or leave a placeholder. Python provides three control statements for this purpose:

Why do we need control statements?

• Searching: Stop as soon as the target is found — no need to keep looping.
• Filtering: Skip values that don't meet a condition.
• Early termination: Exit a loop when an error or invalid input is detected.
• Placeholders: Mark code that will be filled in later, without causing an error.

3.1 Definition

The break statement immediately terminates the loop in which it appears. Control jumps to the first statement after the loop.

3.2 Syntax

for variable in sequence:
    if condition:
        break
    statement(s)

3.3 Key Points

• Exits the innermost loop only (in a nested loop).
• Works with both for and while.
• Any statements after break in the same block are skipped.
• If the loop has an else clause, the else is skipped when break executes.

Flowchart — break

Fig 1. Flowchart showing break — exit the loop as soon as the target is found.

3.4 Example Programs — break

Example 1: Break out of a for loop

for i in range(1, 11):
    if i == 5:
        break
    print(i)
print("Loop ended.")

Explanation: When i reaches 5, break exits the loop. Values 5 to 10 are not printed.

Example 2: Search for an element in a list

numbers = [10, 20, 30, 40, 50]
target = int(input("Enter number to search: "))

for num in numbers:
    if num == target:
        print(target, "found in the list!")
        break
else:
    print(target, "not found.")

Example 3: break in a while loop

n = 1
while True:
    print(n)
    n += 1
    if n > 5:
        break

Example 4: Menu-driven program using break

while True:
    print("\n--- Menu ---")
    print("1. Say Hello")
    print("2. Say Bye")
    print("3. Exit")
    choice = input("Enter choice: ")

    if choice == "1":
        print("Hello!")
    elif choice == "2":
        print("Bye!")
    elif choice == "3":
        print("Exiting...")
        break
    else:
        print("Invalid choice.")

Example 5: break in a nested loop (exits only inner loop)

for i in range(1, 4):
    for j in range(1, 4):
        if j == 2:
            break
        print("i =", i, " j =", j)

Explanation: The break exits the inner loop only. The outer loop continues normally.

4.1 Definition

The continue statement skips the rest of the current iteration and jumps to the next iteration of the loop. The loop does not terminate.

4.2 Syntax

for variable in sequence:
    if condition:
        continue
    statement(s)

4.3 Key Points

• Statements after continue in the same block are skipped for the current iteration.
• Works with both for and while.
• In a while loop, the condition must eventually become False, otherwise you get an infinite loop.
• The loop else clause does execute if the loop finishes normally (no break).

Flowchart — continue

Fig 2. Flowchart showing continue — skip the rest of the current iteration and move to the next.

4.4 Example Programs — continue

Example 6: Print only odd numbers (skip even)

for i in range(1, 11):
    if i % 2 == 0:
        continue
    print(i)

Example 7: Sum only positive numbers in a list

numbers = [10, -5, 20, -8, 30, -2, 40]
total = 0
for num in numbers:
    if num < 0:
        continue
    total += num
print("Sum of positive numbers:", total)

Example 8: continue in a while loop

n = 0
while n < 10:
    n += 1
    if n == 5:
        continue
    print(n)

Example 9: Skip vowels in a string

word = "programming"
for ch in word:
    if ch in "aeiou":
        continue
    print(ch, end=" ")

Example 10: Print only multiples of 3 in a range

for i in range(1, 21):
    if i % 3 != 0:
        continue
    print(i, end=" ")

5.1 Definition

The pass statement is a null statement — it does nothing at runtime. It is used as a placeholder where Python syntax requires a statement but no action is needed.

5.2 Syntax

if condition:
    pass   # to be implemented later

5.3 Key Points

• Does nothing — it is a placeholder.
• Prevents a syntax error in an empty block.
• Useful during development when you plan to fill in code later.
• Can be used inside for, while, if, functions and classes.

Flowchart — pass

Fig 3. Flowchart showing pass — a no-operation placeholder that lets the loop continue normally.

5.4 Example Programs — pass

Example 11: pass as a placeholder in a loop

for i in range(1, 6):
    if i == 3:
        pass    # TODO: implement special case for 3
    else:
        print(i)

Example 12: pass in an empty function

def my_function():
    pass   # to be implemented later

my_function()
print("Function called successfully.")

Example 13: pass in an empty class

class Student:
    pass   # class body to be defined later

s = Student()
print("Object created:", s)

Example 14: pass inside if block

x = 10
if x > 0:
    pass   # positive number — nothing to do
else:
    print("Non-positive")

print("Program finished.")

Example 15: break and continue together

for i in range(1, 11):
    if i == 8:
        break          # stop the loop at 8
    if i % 2 == 0:
        continue       # skip even numbers
    print(i)           # prints odd numbers before 8

Explanation: Even numbers are skipped (continue); when i reaches 8, break ends the loop.

Example 16: break with loop else

numbers = [10, 20, 30, 40, 50]
target = int(input("Enter target: "))

for num in numbers:
    if num == target:
        print("Found", target)
        break
else:
    print(target, "not found.")

Explanation: If break executes, the else block is skipped. If the loop finishes without break, else runs.

Example 17: Password attempt with continue

correct_password = "python123"

for attempt in range(1, 4):
    password = input(f"Attempt {attempt} — Enter password: ")
    if password != correct_password:
        print("Wrong password. Try again.")
        continue
    print("Login successful!")
    break
else:
    print("Account locked. Too many failed attempts.")

Example 18: Skip multiples of 3 and stop at 15

for i in range(1, 21):
    if i == 15:
        break
    if i % 3 == 0:
        continue
    print(i, end=" ")

Example 19: pass placeholder with continue

for i in range(1, 8):
    if i == 4:
        pass        # skip — no action for now
        continue
    if i == 6:
        break
    print(i)

Explanation: At i = 4, pass does nothing and continue skips the print. At i = 6, break exits the loop.

1. What is the purpose of control statements in loops?
2. Differentiate between break and continue with examples.
3. What is the difference between continue and pass?
4. When does the else clause of a loop execute?
5. How does break behave inside a nested loop?
6. Why can continue cause an infinite loop in a while loop? How can you avoid it?
7. Write a Python program to find the first even number in a list using break.
8. Write a Python program to print only the odd numbers from 1 to 20 using continue.
9. Write a Python program that uses pass as a placeholder for a function that is not yet implemented.
10. Explain the output of:

    for i in range(1, 6):
        if i == 3:
            continue
        if i == 5:
            break
        print(i)