03 Control Strutures

Control Structures #

Control structures are used to control the execution flow of the program.

bool Data Type #

Valid values are True and False. Comparisons yield these values. Used in condition and logical operations.

>>> # Booleans represent True or False
>>> t = True
>>> f = False

>>> # Check the type of a boolean
>>> type(t)
<class 'bool'>

>>> # Boolean operations
>>> t and f  # Logical AND (yields True if both operands are True)
False
>>> t or f  # Logical OR (yields True if any of the operands is True)
True
>>> not t  # Logical NOT
False

>>> # Booleans with comparison operators
>>> 5 > 3 
True
>>> 5 < 3
False
>>> 5 == 5 
True
>>> 5 != 3
True

>>> # Combining comparisons
>>> 5 > 3 and 2 < 4
True
>>> 5 > 3 or 2 > 4
True
>>> not (5 > 3)
False

>>> # Booleans with arithmetic operations
>>> True + 1  # True is treated as 1
2
>>> False + 1  # False is treated as 0
1

>>> # Boolean casting 
>>> bool(1)  # Non-zero numbers are True
True
>>> bool(0)  # Zero is False
False
>>> bool("Hello")  # Non-empty strings are True
True
>>> bool("")  # Empty strings are False
False
>>> bool([])  # Empty lists are False
False
>>> bool([1, 2, 3])  # Non-empty lists are True
True

>>> age = 19
>>> is_adult = age >= 18    # expression + assignment
>>> is_adult
True

None Data Type #

None is a special constant in Python that represents the absence of a value or a null value.

>>> x = None
>>> x is None
True
>>> x is not None
False
>>>

Conditionals #

Conditionals in a programming language are used to make decisions in the flow of a program based on whether certain conditions are met. They allow the program to execute different code paths depending on the evaluation of a condition (True or False).

if Statement #

The if statement allows executing a block of code if a condition is True.

x = 10
if x > 5:
    print("x is greater than 5")  # Output: x is greater than 5

Nested Conditions #

x = 10
if x > 5:
    if x < 15:
        print("x is between 5 and 15")  # Output: x is between 5 and 15

Logical Operations in Conditions #

Combine conditions using and, or, and not.

x = 10
if x > 5 and x < 15:
    print("x is between 5 and 15")  # Output: x is between 5 and 15

if-else Statement #

Adds an alternative block when the condition is False.

x = 3
if x > 5:
    print("x is greater than 5")
else:
    print("x is not greater than 5")  # Output: x is not greater than 5

if-elif-else Statement #

x = 7
if x > 10:
    print("x is greater than 10")
elif x > 5:
    print("x is greater than 5 but not more than 10")  # Output
else:
    print("x is 5 or less")

There can be any number of elif sections.

Loops #

Loops execute a block of code repeatedly, saving time and effort. They’re used for:

  • Repetition: Automate repetitive tasks. Example: Printing numbers 1 to 10.
  • Iteration: Process items in a sequence (e.g., list or string). Example: Summing numbers in a list.
  • Conditional Repetition. Example: Prompt user until input is valid.

while loop #

Repeats as long as the condition is True.

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

break and continue #

  • break exits the loop.
  • continue skips to the next iteration.
x = 0
while x < 5:
    x += 1
    if x == 3:
        continue
    if x == 5:
        break
    print(x)  # Output: 1 2 4

Both keywords work in both while and for loops.

for loop #

Iterates over a sequence.

for i in [1, 2, 3]:
    print(i)  # Output: 1 2 3

range() function #

Generates a sequence of numbers.

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

nested loops #

Loops inside loops for multi-dimensional iteration.

for i in range(1, 3):
    for j in range(1, 3):
        print(f"i={i}, j={j}")

infinite loops #

while True:
    print("Infinite Loop")

Break out of the loop by pressing CTRL-C.

pass #

A placeholder that does nothing but satisfies syntax requirements.

for i in range(3):
    pass  # Placeholder for future code

Homework (graded) #

conditionals #

Create a calculator that will ask the user for operand1, operation (+/-/*/division), operand2 and will read the values, convert them to numbers and print the result

loops #

Create a Number Guessing Game in Python. Write a Python program that allows a user to guess a secret number between 1 and 10. The program should guide the user by providing feedback on whether their guess is too low, too high, or correct. The game continues until the user guesses the correct number.

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