Conditional logic (if-then decisions) in Intro to Computing - Flowchart & Logic Diagram

Process Overview

Conditional logic helps a computer decide what to do next by checking if something is true or false. It’s like making a choice based on a question.

Flowchart

Check condition

↓

Do action

This flowchart shows a simple if-then decision: the computer checks a condition, then does one action if true, or another if false, then ends.

Step-by-Step Trace - 5 Steps

Step 1: Start the decision process

Step 2: Check if the condition is true

Step 3: If condition is true, do the first action

Step 4: If condition is false, do the other action

Step 5: End the decision process

Diagram

Check condition

↓

Take umbrella

This diagram shows a real-life example of conditional logic: if it is raining, take an umbrella; if not, wear sunglasses.

Flowchart Quiz - 3 Questions

What happens if the condition is true?

A The computer skips the action

B The computer does the other action

C The computer does the first action

D The computer ends immediately

Key Result

Conditional logic lets computers choose between two actions based on a true or false question.

Practice

1.

What does an if statement do in a program?

easy

A. It stores data in a list.

B. It repeats code multiple times.

C. It checks a condition and runs code only if the condition is true.

D. It creates a new variable.

Solution

1. Step 1: Understand the purpose of if

   An if statement asks a question that can be true or false.

2. Step 2: Identify what happens when the condition is true

   If the condition is true, the program runs the code inside the if block; otherwise, it skips it.

3. Final Answer:

   It checks a condition and runs code only if the condition is true. -> Option C

4. Quick Check:

   if = condition check [OK]

Hint: Remember: if means 'only if true' run code [OK]

Common Mistakes:

• Thinking if repeats code like a loop
• Confusing if with data storage
• Believing if creates variables

2.

Which of the following is the correct syntax for an if statement in Python?

___ x > 10:
    print("x is greater than 10")

easy

A. else

B. for

C. while

D. if

Solution

1. Step 1: Identify the keyword for condition checking

   Python uses if to start a condition check.

2. Step 2: Match the syntax with the code block

   The colon : after the condition is required to start the indented block.

3. Final Answer:

   if -> Option D

4. Quick Check:

   Python if syntax = if [OK]

Hint: If checking condition, start with 'if' keyword [OK]

Common Mistakes:

• Using 'for' or 'while' instead of 'if'
• Forgetting the colon after the condition
• Using 'else' without an 'if'

3.

What will be printed by this Python code?

age = 20
if age >= 18:
    print("Adult")
else:
    print("Child")

medium

A. Adult

B. No output

C. Child

D. Error

Solution

1. Step 1: Check the condition age >= 18

   Variable age is 20, which is greater than or equal to 18, so condition is true.

2. Step 2: Determine which block runs

   Since condition is true, the print("Adult") line runs, printing "Adult".

3. Final Answer:

   Adult -> Option A

4. Quick Check:

   20 >= 18 = Adult [OK]

Hint: Check if condition is true to pick printed output [OK]

Common Mistakes:

• Choosing 'Child' without checking condition
• Thinking no output if condition true
• Assuming syntax error

4.

Find the error in this code snippet:

if score > 50
    print("Pass")
else:
    print("Fail")

medium

A. Wrong indentation of print statements

B. Missing colon after if condition

C. Using else without if

D. Incorrect comparison operator

Solution

1. Step 1: Check syntax of if statement

   Python requires a colon : at the end of the if condition line.

2. Step 2: Identify the missing colon

   The line if score > 50 is missing the colon, causing a syntax error.

3. Final Answer:

   Missing colon after if condition -> Option B

4. Quick Check:

   Colon needed after if condition [OK]

Hint: Look for missing colon after if condition line [OK]

Common Mistakes:

• Ignoring missing colon error
• Thinking indentation is wrong here
• Confusing else usage

5.

You want to write a program that prints "Good morning" if the hour is less than 12, and "Good afternoon" otherwise. Which code correctly implements this?

hour = 10
___ hour < 12:
    print("Good morning")
else:
    print("Good afternoon")

hard

A. if

B. else if

C. elif

D. while

Solution

1. Step 1: Choose the correct keyword for the first condition

   The first condition must start with if to check if hour < 12.

2. Step 2: Use else for the alternative

   The else block runs if the if condition is false, printing "Good afternoon".

3. Final Answer:

   if -> Option A

4. Quick Check:

   Use if for first condition, else for alternative [OK]

Hint: Start conditions with if, alternatives with else [OK]

Common Mistakes:

• Using 'else if' instead of 'if' in Python
• Using 'elif' without a preceding if
• Using 'while' instead of if for decisions