CS 115: If Statements and Boolean Operations
Mathematical Operations
Basic Operators
Addition (+)
Example: 15 + 3 = 18
Subtraction (-)
Example: 15 - 3 = 12
Multiplication (*)
Example: 15 * 3 = 45
Division (/)
Example: 15 / 3 = 5
Other Operators
Integer Division (//)
Example: 5 // 3 = 1
Modulus (%)
Example: 5 mod 3 = 2
Exponentiation (**)
Example: 5 ** 3 = 125
Comparison Operations
Compares the values on either side; also called relational operators.
Common Operators
Greater than (>)
Example: 15 > 3 # is True
Greater than or equal (>=)
Example: 15 >= 3 # is True
Less than (<)
Example: 15 < 3 # is False
Less than or equal (<=)
Example: 15 <= 3 # is False
Not equal (!=)
Example: 15 != 3 # is True
Equal (==)
Example: 15 == 3 # is False
Examples of Comparison Operators
```python
print(4 > 2) # True
print(7 == 8) # False
print(10 <= 10) # True print(5 != 5) # False print(3 < 1) # False print(9 >= 6) # True
- Additional Variable Examples:
python
a = 6
b = 10
print(a < b) # True print(a == b) # False print(b >= 10) # True
print(a != 6) # False
---
## Logical Operators
- Logical Operators combine or modify boolean expressions, including relational expressions.
### Types of Logical Operators
- **And Operator**
- Syntax: **expression1 and expression2**
- Result: True only if both expressions are True.
- **Or Operator**
- Syntax: **expression1 or expression2**
- Result: True if at least one expression is True.
- **Not Operator**
- Syntax: **not expression**
- Result: Flips the value (True becomes False, False becomes True).
### Examples of Logical Operators
python
a = 10
b = 5
c = 3
print(a > 5 and b < 10) # True print(a < 5 or b == 5) # True print(not (a == 10)) # False print(a < 20 or b > 10) # True
print(not (b <= 5 and c == 3)) # False
print(not (c != 3)) # True
---
## If Branching (Conditional Statements)
- A branch is a program path taken based on an expression's value.
### How If Branching Works
- **If branching**: The branch is taken if an expression evaluates to True.
### Visual Representation
- Flowchart:
- Condition Statements
- Direction: Start -> Check Condition -> If True -> Execute Statement
### Example of If Branching
- Condition: Extra baggage fee is $25 when a suitcase is over 50 lb.
- Conditional Statement: ext{weight} > 50
### Python Notation for If Branching
- Syntax:
python
if condition:
statement(s)
- Indentation: Must use 4 spaces or a tab and never mix spaces and tabs.
#### Example: If Branching in Python
python
if weight > 50:
print(“baggage fee is $25”)
---
## Exercise: If Branching Implementation
### Task: Complete the Program
- Prompt for user's input based on weight:
python
if weight > 50:
print(“baggage fee is $25”)
### Prompt Implementation
- Full Solution:
python
weight = float(input(“Enter bag weight”))
if weight > 50:
print(“baggage fee is $25”)
---
## Activity 11: If Statements Programming
### Task: Write a program that prompts an extra baggage fee of $50 when:
- The baggage is over 50 lb
- The linear length is over 62 inches.
### Example Outputs
- User input: 60 lb & 75 inches should output:
- “Extra baggage fee is $50”
- User input: 50 lb & 65 inches should output:
- “Extra baggage fee is $50”
---
## If-Else Statements
- An if-else has two branches:
- Branch 1: Taken when the condition is True
- Branch 2: Taken when the condition is False
### Diagram
- Condition -> Start -> Branch 1 (if True) -> Execute Statements -> Stop
- Otherwise, go to Branch 2 (if False) -> Execute Statements -> Stop
### Example of If-Else in Python:
- Program checks if a number is between 0 and 10
python
if (0 < number) and (number < 10):
print(“The number is between 0 and 10”)
else:
print(“Number is out of range”)
---
## Activity 12: If-Else Statements Programming
### Task: Write a program that prompts an extra baggage fee of $50 when conditions are met, otherwise show no fee.
### Example Outputs
- Input: 60 lb & 75 inches outputs:
- “Extra baggage fee is $50”
- Input: 50 lb & 55 inches outputs:
- “No extra baggage fee”
---
## More on If-Else: Example Scenario
- Create a program determining if a student has passed based on their final score.
- If the student passes, add a congratulatory message; otherwise, suggest to study more.
- Define passing score: 60.
### Diagram
- Condition: score > 60, another path if False leads to “You have failed!”
### Python Code Example
python
score = float(input(“Enter score: ”))
if score > 60:
print(“You have passed!”)
print(“Congratulations”)
else:
print(“You have failed!”)
print(“Review the material”)
---
## Multi-branch If-Else Statements
- This structure can be extended to have three or more branches, with sequences checked.
### Diagram
- Condition 1 leads to Branch 1, else proceed to Condition 2 for Branch 2, else to Branch 3.
### Python Notation for Multi-branch
python
if condition1:
# branch 1 statement(s)
elif condition2:
# branch 2 statement(s)
else:
# branch 3 statement(s)
---
## Multi-Branch If-Else: Temperature Program Example
- Request user to enter the temperature and provide messages based on input.
### Conditions to Check
- If temperature > 90, output: "It's a hot day."
- If temperature > 70, output: "It's a nice day."
- If temperature > 50, output: "It's a bit chilly."
- For any temperature below, output: "It's cold outside."
### Python Code Example
python
temp = float(input("Enter temperature: "))
if temp > 90:
print("It's a hot day.")
elif temp > 70:
print("It's a nice day.")
elif temp > 50:
print("It's a bit chilly.")
else:
print("It's cold outside.")
```
Activity 13: Multi-Branch If-Else Statements Programming
Task: Prompt user for the final score for CS 115 and display the letter grade based on the score.
Example Outputs
Input: Enter score: 70 → “Your final grade is C-”
Input: Enter score: 91 → “Your final grade is A-”
Activity 14: Informal Feedback
Task: Complete the informal mid-semester feedback survey and confirm in Piazza activity 14 thread.
Note: Must use ODU account; your email will not be recorded by the form.
Link: https://forms.gle/GFUL5LUceXJiszWD7