Day 3 - Control Flow and Logical Operators

Control Flow with if / else and Conditional Operators

if / else Statement :

If Statement: Checks a condition. If the condition is True,

the code inside the if block runs.

Else Statement: Runs if the if condition is False

Critical Points

The condition in the if the statement must be evaluated to True or False.

Indentation is crucial in Python; the code inside if or else must be indented.

Condition Check

Conditionals in Python to check a condition and tell the computer what to do in each case.

Example

if <this condition is true>:

<then execute this line of code>

What if the condition is false?

The else keyword is used to define a block of code that will execute if the condition checked in the if statement is false.

if cow can fly:

else:
    print("This is real life")

Comparator Operators

\> Greater than

< Less than

\>= Greater than or equal to

<= Less than or equal to

\== Equal to

!= Not equal to

Key Points

Conditional operators are used for comparisons.

They are often combined with if-else statements for decision-making.

They always return True or False.

List of Conditional Operators

Modulo Operator (%) in Python

The modulo operator (%) returns the remainder when one number is divided by another.

It’s commonly used in programming for tasks like finding even/odd numbers.

Example

result = a % b

---

a: Dividend (number being divided)

b: Divisor (number dividing)

result: Remainder after division

If a is divisible by b, the result is 0.
Example: 10 % 5 gives 0.

Nested if statement and elif statement

A nested if statement is an if statement inside another if statement.

It allows for checking a condition only if a previous condition is True.

This structure is useful when decisions are dependent on

Example

You can put if/else statements inside other if/else statements. This is known as nesting. e.g.

if maths_score >= 90:
    if english_score >= 90:
        print("You're good at everything")
    else:
        print("You're good at maths")
if english_score >= 90:
    print("You're good at english)

Output

You are good at everything

In this case, only when a student has over 90 in maths and English, get

You are good at everything.

Key point:

You can also haveif statements that don't have a paired else statement.

Elif Statement in Python

The elif statement (short for "else if") allows you to check multiple conditions.

If one condition is True, the corresponding block of code runs, and the

remaining conditions are skipped.

Example

marks = 85

if marks >= 90:
    print("Grade: A")
elif marks >= 80:
    print("Grade: B")
elif marks >= 70:
    print("Grade: C")
else:
    print("Grade: F")

Output

Grade: B

Key Differences:

Nested if: Used when one condition depends on another condition being True.

Elif: Used to check multiple independent conditions.

Combining Both:

You can use both nested if and elif in the same code.

age = 25
has_ticket = True

if age >= 18:
    if has_ticket:
        print("You can enter the event.")
    else:
        print("You need a ticket.")
elif age >= 13:
    print("You can enter with an adult.")
else:
    print("You are too young to enter.")

Output

You can enter the event.

Multiple if Statements

A nested if statement is an ifstatement placed inside another if or else block.

It allows for checking multiple conditions

age = 25
has_ticket = True
is_vip = False

if age >= 18:
    print("You are old enough to enter.")

if has_ticket:
    print("You have a ticket.")

if is_vip:
    print("You have VIP access.")

Output

You are old enough to enter.
You have a ticket.

Key Points About Multiple if Statements:

Each ifstatement is evaluated independently.
If multiple conditions are True, all their corresponding blocks will execute.

Order Matters:
Since all if statements are evaluated, and the order of conditions can impact the flow of the program.

Different from if-elif:

In if-elif, only one block of code runs when a condition is True.

In multiple if statements, more than one block can run.

When to Use Multiple if Statements:

When you check multiple conditions Independent.

When multiple conditions can be true simultaneously.

Logical Operators

Logical operators in Python are used to combine or modify

conditional statements. They return a Boolean value

(True or False)based on the logic of the conditions provided.

Types of Logical Operators

1. and (Logical AND)

Combines two conditions.

Returns True only if both conditions are True.

If either condition is False, it returns False.

2. or (Logical OR)

Combines two conditions.

Returns True if at least one condition is True.

Returns False only if both conditions are False.

3. not (Logical NOT)

Reverses the logical state of a condition.

If the condition is True, not makes it False, and vice versa.

When to Use Logical Operators

Use and when all conditions need to be True.

Use or when at least one condition needs to be True.

Use not to reverse the logic of a condition.

Truth Table for Logical Operators

Key Highlights

if/else Statements: Control the program's flow by executing code blocks based on conditions.

Comparator Operators: Enable comparisons like ==, !=, <, and >.

Nested if and elif: Handle dependent and independent conditions effectively.

Logical Operators: Combine conditions using and, or, and not.

What's next in my journey?

On Day 3 of the 100 Days of Python, I will learn about

Randomisation and Python lists.