Python if else

In Python, if-else statements are used for decision-making. They allow you to execute certain pieces of code based on whether a certain condition is true or false. 

Syntax of if-else Statement:

if condition:
    # block of code to be executed if the condition is true
else:
    # block of code to be executed if the condition is false

Basic if-else Statement

# Checking if a number is positive or negative
num = 10

if num >= 0:
    print("Number is positive or zero")
else:
    print("Number is negative")

Here -

num >= 0 is the condition being checked.
If num is greater than or equal to zero, "Number is positive or zero" will be printed.

Otherwise, "Number is negative" will be printed.

Nested if-else Statements

# Checking if a number is positive, negative, or zero
num = -5

if num > 0:
    print("Number is positive")
elif num == 0:
    print("Number is zero")
else:
    print("Number is negative")

Here -

The condition num > 0 is checked first.
If true, "Number is positive" is printed.
If false, the elif num == 0 condition is checked.
If num equals zero, "Number is zero" is printed.
If both conditions are false, "Number is negative" is printed.

# Checking multiple conditions using logical operators
num = 7

if num % 2 == 0 and num > 0:
    print("Number is positive and even")
elif num % 2 != 0 and num > 0:
    print("Number is positive and odd")
elif num == 0:
    print("Number is zero")
else:
    print("Number is negative")

Here -

The and operator (and) is used to combine conditions.
num % 2 == 0 checks if num is even.
num % 2 != 0 checks if num is odd.
num > 0 checks if num is positive.
The elif statement allows us to check multiple conditions sequentially until one is true.

if-else with Ternary Operator (Conditional Expression)

# Ternary operator usage
a = 10
b = 20

max_num = a if a > b else b
print("Maximum number is:", max_num)

Here -

The ternary operator (a if condition else b) allows us to assign a value to max_num based on a condition (a > b).
If a is greater than b, max_num will be assigned a, otherwise b.

Properties of if-else Statements:

1. Decision-making - if-else statements help in making decisions based on conditions.
2. Flexibility - You can use if, elif (short for "else if"), and else together to handle multiple cases.
3. Nested Statements -  You can nest if-else statements within each other to handle more complex scenarios.
4. Ternary Operator - Python also supports a concise ternary operator for simple conditional assignments.

Understanding if-else statements is fundamental in programming as they allow you to control the flow of your code based on various conditions, making your programs more dynamic and responsive.