Loops (repeating actions) in Intro to Computing - Draw & Build Visually

Draw This - beginner

Draw a flowchart that repeats the action of printing numbers from 1 to 5 using a loop.

7 minutes

Hint 1

Hint 2

Hint 3

Grading Criteria

Start and End symbols present

Initialization of loop variable shown

Decision diamond correctly checks loop condition

Loop body includes print and increment steps

Flow returns to decision after increment

Loop ends when condition is false

Solution

  +---------------------+
  |       Start         |
  +----------+----------+
             |
             v
  +---------------------+
  | Set number = 1      |
  +----------+----------+
             |
             v
  +---------------------+
  | Is number <= 5?     |<----------------+
  +----------+----------+                 |
             | Yes                        |
             v                            |
  +---------------------+                |
  | Print number        |                |
  +----------+----------+                |
             |                           |
             v                           |
  +---------------------+                |
  | number = number + 1 |                |
  +----------+----------+                |
             |                           |
             +---------------------------+
             |
             v
  +---------------------+
  |        End          |
  +---------------------+

This flowchart starts by setting a variable number to 1.

It then checks if number is less than or equal to 5.

If yes, it prints the current number, then adds 1 to number.

The flow returns to the decision to check the condition again.

When number becomes 6, the condition fails and the flowchart ends.

This repeats the print action 5 times, printing numbers 1 through 5.

Variations - 2 Challenges

[intermediate] Draw a flowchart that prints even numbers from 2 to 10 using a loop.

[advanced] Draw a flowchart that asks the user to enter a password repeatedly until the correct password 'secret' is entered.

Practice

1. What is the main purpose of a loop in programming?

easy

A. To display text on the screen

B. To store data permanently

C. To repeat a set of actions multiple times

D. To create a new variable

Solution

1. Step 1: Understand the role of loops

   Loops are used to repeat actions without writing the same code again and again.

2. Step 2: Identify the correct purpose

   Repeating a set of actions multiple times matches the purpose of loops.

3. Final Answer:

   To repeat a set of actions multiple times -> Option C

4. Quick Check:

   Loops = Repeat actions [OK]

Hint: Loops repeat tasks to save writing code again [OK]

Common Mistakes:

• Confusing loops with data storage
• Thinking loops create variables
• Believing loops only display text

2. Which of the following is the correct syntax for a for loop in Python to repeat 5 times?

easy

A. for i to 5:

B. for i in range(5):

C. loop i from 1 to 5:

D. repeat 5 times:

Solution

1. Step 1: Recall Python for loop syntax

   Python uses for variable in range(number): to repeat actions a set number of times.

2. Step 2: Match the correct syntax

   for i in range(5): correctly repeats 5 times from 0 to 4.

3. Final Answer:

   for i in range(5): -> Option B

4. Quick Check:

   Python for loop = for i in range(5): [OK]

Hint: Python for loops use 'for variable in range():' [OK]

Common Mistakes:

• Using 'for i to 5:' which is invalid syntax
• Confusing loop syntax with other languages
• Missing colon at the end of the loop line

3. What will be the output of this Python code?

sum = 0
for i in range(3):
    sum += i
print(sum)

medium

A. 6

B. 3

C. 0

D. SyntaxError

Solution

1. Step 1: Trace the loop iterations

   The loop runs with i = 0, 1, 2. sum starts at 0.

2. Step 2: Calculate sum after each iteration

   Iteration 1: sum = 0 + 0 = 0
   Iteration 2: sum = 0 + 1 = 1
   Iteration 3: sum = 1 + 2 = 3

3. Step 3: Sum all values

   Sum of 0 + 1 + 2 = 3, but the code adds i each iteration, so final sum is 3.

4. Final Answer:

   3 -> Option A

5. Quick Check:

   0+1+2 = 3 [OK]

Hint: Add all numbers from 0 up to 2 [OK]

Common Mistakes:

• Adding 3 instead of stopping at 2
• Confusing range(3) with range(1,3)
• Expecting SyntaxError due to indentation

4. Identify the error in this loop code:

i = 1
while i < 4
    print(i)
    i += 1

medium

A. Missing colon after while condition

B. Variable i should start at 0

C. print() should be outside the loop

D. i += 1 should be before print()

Solution

1. Step 1: Check while loop syntax

   Python requires a colon ':' after the while condition to start the loop block.

2. Step 2: Identify the missing colon

   The code misses ':' after while i < 4, causing a syntax error.

3. Final Answer:

   Missing colon after while condition -> Option A

4. Quick Check:

   while condition needs ':' [OK]

Hint: Always put ':' after while condition [OK]

Common Mistakes:

• Ignoring missing colon error
• Changing variable start unnecessarily
• Moving print() outside loop incorrectly

5. You want to print all even numbers from 2 to 10 using a loop. Which code snippet correctly does this?

hard

A. for i in range(2, 11, 2):
print(i)

B. for i in range(1, 11):
if i % 2 == 0:
print(i)

C. i = 2
while i <= 10:
print(i)
i += 2

D. All of the above

Solution

1. Step 1: Analyze each code snippet

   for i in range(2, 11, 2): print(i) uses for loop with step 2 from 2 to 10.
   for i in range(1, 11): if i % 2 == 0: print(i) uses for loop with condition to print even numbers.
   i = 2 while i <= 10: print(i) i += 2 uses while loop increasing by 2 starting at 2.

2. Step 2: Confirm all snippets print even numbers 2 to 10

   All three snippets correctly print 2, 4, 6, 8, 10.

3. Final Answer:

   All of the above -> Option D

4. Quick Check:

   All methods print even numbers 2 to 10 [OK]

Hint: Multiple loop types can print even numbers correctly [OK]

Common Mistakes:

• Using wrong range end value
• Forgetting to increment in while loop
• Not checking condition for even numbers