Control flow in python

 

Control flow in Python refers to the order in which statements are executed in a program. It helps you make decisions, repeat tasks, and control how your code runs.

Here’s a clear and beginner-friendly explanation:

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✅ 1. Conditional Statements (Decision Making)

Used to run specific code based on conditions.

if statement

x = 10
if x > 5:
    print("x is greater than 5")

if-else statement

age = 17
if age >= 18:
    print("You can vote")
else:
    print("You cannot vote")

if-elif-else

marks = 85

if marks >= 90:
    print("Grade A")
elif marks >= 75:
    print("Grade B")
else:
    print("Grade C")

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✅ 2. Loops (Repeating Tasks)

➡ for loop

Used to iterate over sequences (list, string, range, etc.)

Example:

for i in range(5):
    print(i)

Looping through a list:

fruits = ["apple", "banana", "mango"]
for fruit in fruits:
    print(fruit)

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➡ while loop

Runs as long as a condition is true.

count = 1
while count <= 5:
    print(count)
    count += 1

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✅ 3. Loop Control Statements

break → stop the loop immediately

for i in range(10):
    if i == 5:
        break
    print(i)

continue → skip the current iteration

for i in range(5):
    if i == 2:
        continue
    print(i)

pass → placeholder, does nothing

for i in range(5):
    pass  # future code can go here

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🎯 Summary Table

Concept	Use
if	Check a condition
if-else	Decision making
elif	Multiple conditions
for	Loop through sequences
while	Loop until condition false
break	Stop loop
continue	Skip iteration
pass	Do nothing (placeholder)

Here’s more detailed and advanced concepts of Control Flow in Python, including examples, diagrams, and practice problems.

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⭐ 1. Nested Control Flow

You can put one control structure inside another.

Example: Nested if

age = 20
citizen = True

if age >= 18:
    if citizen:
        print("Eligible to vote")
    else:
        print("Not a citizen")
else:
    print("Underage")

Example: Nested Loops

for i in range(3):
    for j in range(2):
        print(i, j)

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⭐ 2. Loop with else

Python has a unique feature:

for…else

The else block executes only if the loop completes normally (without a break).

for num in [1, 2, 3]:
    print(num)
else:
    print("Loop finished")

Useful Example:

Search for an element:

nums = [10, 20, 30, 40]

for n in nums:
    if n == 25:
        print("Found!")
        break
else:
    print("Not found!")

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⭐ 3. while…else

Same concept as for…else.

count = 1
while count <= 3:
    print(count)
    count += 1
else:
    print("Loop ended normally")

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⭐ 4. Range Variations

range() can take 1, 2, or 3 arguments.

Example:

range(5)        # 0 to 4
range(2, 6)     # 2 to 5
range(1, 10, 2) # 1, 3, 5, 7, 9

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⭐ 5. Infinite Loops

A loop that never ends unless you break it.

while True:
    name = input("Enter name (or 'stop'): ")
    if name == "stop":
        break

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⭐ 6. Logical Operators in Control Flow

Operator	Meaning
and	True if both conditions are true
or	True if any condition is true
not	Reverses the condition

Example:

age = 20
has_license = True

if age >= 18 and has_license:
    print("You can drive")

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⭐ 7. Using break and continue in loops

break example:

for i in range(10):
    if i == 4:
        break
    print(i)

continue example:

for i in range(5):
    if i == 3:
        continue
    print(i)

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⭐ 8. pass Statement

pass is used as a placeholder.

if True:
    pass  # TODO: Write logic later

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⭐ 9. Control Flow with Match Case (Python 3.10+)

Like switch-case in other languages.

status = 2

match status:
    case 1:
        print("Start")
    case 2:
        print("Processing")
    case 3:
        print("Completed")
    case _:
        print("Unknown")

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⭐ Practice Questions (with increasing difficulty)

Level 1 (Basic)

1. Write a program to check if a number is positive, negative, or zero.
2. Print numbers from 1 to 10 using a loop.
3. Print even numbers from 1 to 20.

Level 2 (Intermediate)

4. Write a program to find the sum of digits of a number.
5. Use a while loop to print a multiplication table of any number.
6. Use a for-else loop to search an element in a list.

Level 3 (Advanced)

7. Write a program to check if a number is a prime number.
8. Use nested loops to print a pattern:

*
**
***
****

9. Use match-case to display menu choices (1–Start, 2–Stop, etc.)

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