Conditional Statements in Python & Control Flow Statements

Conditional statements

Conditional statements allow you to execute a block of code only if a specific condition is true.

Syntax

if condition:
    # code to execute if condition is true
elif another_condition:
    # code to execute if another_condition is true
else:
    # code to execute if all conditions are false

Examples

1. Simple if statement

age = 18
if age >= 18:
    print("You are eligible to vote.")
# Output: You are eligible to vote.

2. if-else statement

num = 10
if num % 2 == 0:
    print("Even number")
else:
    print("Odd number")
# Output: Even number

3. if-elif-else ladder

marks = 85
if marks >= 90:
    print("Grade: A")
elif marks >= 75:
    print("Grade: B")
else:
    print("Grade: C")
# Output: Grade: B

4. Nested if statements

num = 10
if num > 0:
    if num % 2 == 0:
        print("Positive even number")
    else:
        print("Positive odd number")
else:
    print("Negative number or zero")
# Output: Positive even number

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Control Flow Statements

Control flow statements are used to alter the natural sequence of execution in a program.

Types of Control Flow Statements

a. for Loop

Iterates over a sequence (list, tuple, string, etc.).

Example:

for i in range(1, 6):
    print(i)
# Output:
# 1
# 2
# 3
# 4
# 5

b. while Loop

Executes a block of code as long as a condition is true.

Example:

count = 1
while count <= 5:
    print(count)
    count += 1
# Output:
# 1
# 2
# 3
# 4
# 5

c. break

Exits a loop prematurely.

Example:

for i in range(1, 6):
    if i == 3:
        break
    print(i)
# Output:
# 1
# 2

d. continue

Skips the current iteration and moves to the next.

Example:

for i in range(1, 6):
    if i == 3:
        continue
    print(i)
# Output:
# 1
# 2
# 4
# 5

e. pass

Does nothing; a placeholder for future code.

Example:

if True:
    pass  # Code to be added later

f. else with Loops

You can attach an else block to a loop, which executes if the loop completes without a break.

Example:

for i in range(1, 6):
    if i == 3:
        break
else:
    print("Loop completed without a break.")
# Output: (No output because the loop breaks)

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3. Example: Combining Conditional and Control Flow Statements

for i in range(1, 10):
    if i % 2 == 0:
        print(f"{i} is even")
    else:
        print(f"{i} is odd")
# Output:
# 1 is odd
# 2 is even
# 3 is odd
# 4 is even
# 5 is odd
# 6 is even
# 7 is odd
# 8 is even
# 9 is odd