Python • Condition, Loops & Casting

Condition, Loops & Type Casting

Master decision‑making with if‑elif‑else, repeat code with for/while loops, and safely convert data types with casting functions.

🔄

For Loop

Iterates over sequences

🔁

While Loop

Repeats while true

⚙️

range()

Number generator

🔄

Type Casting

int(), float(), str(), bool()

If‑Elif‑Else Statements

The if statement lets you execute code only when a condition is True. Use elif for additional checks and else for a default block.

conditional.py

age = 18
if age < 13:
    print("You are a child")
elif age < 18:
    print("You are a teenager")
else:
    print("You are an adult")

You are an adult

Note: Indentation defines blocks. elif and else are optional.

For Loop

A for loop repeats a block of code for each item in a sequence.

Beginner Example

for_loop_basic.py

fruits = ["apple", "banana", "orange"]
for fruit in fruits:
    print(fruit)
for letter in "Python":
    print(letter)
for i in range(5):
    print(i)

apple
banana
orange
P y t h o n
0 1 2 3 4

Intermediate Example

for_loop_intermediate.py

fruits = ["apple", "banana", "cherry"]
for index, fruit in enumerate(fruits):
    print(f"{index}: {fruit}")
for i in range(1,4):
    for j in range(1,4):
        print(f"{i} x {j} = {i*j}")
for x in range(3):
    print(x)
else:
    print("Loop ended without break")

0: apple
1: banana
2: cherry
multiplication table
0 1 2
Loop ended without break

range() – The Loop Counter

range(start, stop, step) generates sequences.

1️⃣

range(stop)

range(5) → 0,1,2,3,4

2️⃣

range(start, stop)

range(2,6) → 2,3,4,5

3️⃣

range(start, stop, step)

range(1,10,2) → 1,3,5,7,9

range_all.py

for i in range(4): print(i)          # 0 1 2 3
for i in range(10,13): print(i)      # 10 11 12
for i in range(2,11,2): print(i)     # 2 4 6 8 10
for i in range(5,0,-1): print(i)     # 5 4 3 2 1

While Loop

Repeats while condition is True. Use break to exit and continue to skip.

while_basic.py

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

0 1 2 3 4

Type Casting – Converting Between Data Types

Python provides built‑in functions to convert one data type to another. This is essential when handling user input or preparing data for calculations.

Function	Converts to	Example
`int(x)`	Integer	`int("42")` → 42, `int(3.14)` → 3
`float(x)`	Float	`float("3.14")` → 3.14, `float(5)` → 5.0
`str(x)`	String	`str(123)` → "123", `str(4.5)` → "4.5"
`bool(x)`	Boolean	`bool(0)` → False, `bool(5)` → True

Beginner Example: Converting Input

input_casting.py

# input() always returns a string
age_str = input("Enter your age: ")
age = int(age_str)          # convert to int
next_age = age + 1
print(f"Next year you'll be {next_age}")

price = float(input("Enter price: "))
tax = price * 0.18
print(f"Tax = {tax:.2f}")

Enter your age: 15
Next year you'll be 16
Enter price: 100
Tax = 18.00

Intermediate Example: Casting with Conditions

casting_conditions.py

# Convert string to bool – caution: bool("False") is True!
value = input("Enter True or False: ").lower()
bool_val = value == "true"      # manual conversion
print(bool_val)

# Mixing numbers and strings
num = 42
message = "The answer is " + str(num)
print(message)

# Float to int (truncates)
pi = 3.14159
approx = int(pi)
print(approx)   # 3

Enter True or False: true
True
The answer is 42
3

Practice Problems (Solved)

Strengthen conditions, loops, and casting.

🔰 Beginner Level

1. Check If a Number is Prime

num = int(input("Enter number: "))
is_prime = num > 1
for i in range(2, int(num**0.5)+1):
    if num % i == 0:
        is_prime = False
        break
print("Prime" if is_prime else "Not Prime")

2. Sum of First n Natural Numbers

n = int(input("Enter n: "))
total = sum(range(1, n+1))
print(total)

3. Reverse a String (without slicing)

text = input("Enter string: ")
rev = ""
for ch in text:
    rev = ch + rev
print(rev)

4. Safe Division with Casting

Problem: Accept two numbers (as strings), convert to float, and print division result. Handle division by zero.

a = float(input("First number: "))
b = float(input("Second number: "))
if b == 0:
    print("Cannot divide by zero")
else:
    print(f"Result = {a/b:.2f}")

5. Convert String List to Integers

Problem: Given a string of numbers "10 20 30", convert each to integer and find the sum using a loop.

numbers_str = "10 20 30"
parts = numbers_str.split()
total = 0
for p in parts:
    total += int(p)
print("Sum =", total)

⚡ Intermediate Level

6. Fibonacci Series up to n Terms

n = int(input("Terms: "))
a,b = 0,1
for _ in range(n):
    print(a, end=' ')
    a,b = b, a+b

7. Count Digits, Letters, Spaces

s = input("Sentence: ")
d = l = sp = 0
for ch in s:
    if ch.isdigit(): d+=1
    elif ch.isalpha(): l+=1
    elif ch==' ': sp+=1
print(f"Digits:{d} Letters:{l} Spaces:{sp}")

8. Multiplication Table (nested loops)

for i in range(1,11):
    for j in range(1,11):
        print(f"{i*j:4}", end="")
    print()

Unsolved Exercises

Solve these on your own – no solutions provided.

🔰 Beginner Level

1. Print Even Numbers from 1 to 20

Write your code here

2. Countdown Timer

Write your code here

3. Grade Calculator (if‑elif‑else)

Write your code here

4. String to Float & Average

Accept three string numbers (e.g., "85.5 90 78.2"), split, convert to float, and print average.

Write your code here

5. Boolean Casting Practice

Write a program that reads a string "True" or "False" and prints the corresponding boolean value. Also show what happens with empty string.

Write your code here

⚡ Intermediate Level

6. Sum of Digits of a Number

Write your code here

7. Right‑Angled Triangle Pattern

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8. ATM PIN Validation (3 attempts)

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