Unit 2: Control Structures notes, polytechnic 3rd semester python notes

2.1 Conditional Blocks Using if

Conditional blocks in Python allow the execution of specific code based on whether a condition is True or False. The if statement is used to evaluate a condition.

Syntax:

python

if condition:
    # Code to execute if the condition is True

Example:

python

age = 18
if age >= 18:
    print("You are an adult.")

In this example, if age is 18 or more, the message "You are an adult." will be printed.

---

2.2 else and elif

The else statement is used to execute code if the if condition is False. The elif (else if) statement checks multiple conditions in a sequence.

Syntax:

python

if condition1:
    # Code to execute if condition1 is True
elif condition2:
    # Code to execute if condition2 is True
else:
    # Code to execute if both conditions are False

Example:

python

age = 16
if age >= 18:
    print("You are an adult.")
elif age > 12:
    print("You are a teenager.")
else:
    print("You are a child.")

In this example, if age is between 13 and 17, the message "You are a teenager." is printed; otherwise, other statements execute based on the condition.

---

2.3 for Loops and Iterations

A for loop in Python is used to iterate over a sequence (like a list, tuple, or string) and perform a set of actions.

Syntax:

python

for item in sequence:
    # Code to execute for each item in the sequence

Example:

python

for num in range(1, 5):
    print(num)

This code prints numbers from 1 to 4. The range() function generates the numbers in the sequence.

Iterating Over a List:

python

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

This will print each fruit in the list.

---

2.4 while Loops

A while loop repeatedly executes a block of code as long as the given condition is True.

Syntax:

python

while condition:
    # Code to execute while the condition is True

Example:

python

count = 0
while count < 5:
    print(count)
    count += 1

This loop prints the values from 0 to 4 and stops when count becomes 5.

---

2.5 Loop Manipulation Using continue, break, and pass

• break: Terminates the loop prematurely.

  Example:

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

  This loop will stop when num equals 5.

• continue: Skips the current iteration and moves to the next iteration.

  Example:

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

  This will print 0, 1, 2, 4, skipping 3.

• pass: Acts as a placeholder when a statement is required syntactically but no action needs to be performed.

  Example:

  python
  
  for num in range(5):
      if num == 3:
          pass
      print(num)
  

  This does nothing when num is 3 but continues the loop.

---

2.6 Programming Using Conditional and Loop Blocks

By combining conditionals (if, else, elif) and loops (for, while), more complex and dynamic programs can be written.

Example: Find the sum of all even numbers from 1 to 10.

python

sum_of_evens = 0
for num in range(1, 11):
    if num % 2 == 0:
        sum_of_evens += num
print("Sum of even numbers from 1 to 10:", sum_of_evens)

In this program:

• The loop iterates over the numbers from 1 to 10.
• The if statement checks whether the number is even.
• If the number is even, it's added to sum_of_evens.

---

These control structures (conditionals and loops) form the backbone of decision-making and iteration in Python programming. Understanding them is crucial for implementing logic and handling repetitive tasks efficiently.