Loops (repeating actions) in Intro to Computing - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ trace

intermediate

Trace the output of a simple for loop

What will be printed by the following code?

Intro to Computing

for i in range(3):
    print(i * 2)

A 0 2 4

B 0 1 2

C 2 4 6

D 1 3 5

💡 Hint

Remember, range(3) produces 0, 1, 2.

The loop runs with i = 0, 1, 2. Multiplying each by 2 gives 0, 2, 4.

🧠 Conceptual

intermediate

Understanding while loop behavior

What will happen when this code runs?

Intro to Computing

count = 3
while count > 0:
    print(count)
    count -= 1

A Prints 3 2 1 0 then stops

B Prints 3 2 1 then stops

C Prints 1 2 3 then stops

D Runs forever printing 3

💡 Hint

Check the condition count > 0 and how count changes.

The loop prints 3, then 2, then 1. When count becomes 0, the condition fails and loop stops.

❓ Comparison

advanced

Compare outputs of two loops

Which option correctly describes the difference between these two loops?

Loop 1:
for i in range(1, 5):
    print(i)

Loop 2:
i = 1
while i < 5:
    print(i)
    i += 1

A Both print 1 2 3 4 but Loop 1 uses for, Loop 2 uses while

B Loop 1 prints 1 2 3 4, Loop 2 prints 1 2 3 4 5

C Loop 1 prints 0 1 2 3, Loop 2 prints 1 2 3 4

D Loop 1 runs forever, Loop 2 stops after printing 4

💡 Hint

Check the range and condition carefully.

Both loops print numbers 1 to 4. Loop 1 uses for, Loop 2 uses while but output is same.

❓ identification

advanced

Identify the error in loop code

What error will this code cause?

i = 0
while i < 3:
print(i)
i += 1

A No error, prints 0 1 2

B TypeError because i is not a number

C SyntaxError because while is missing a colon

D IndentationError because print and increment are not indented

💡 Hint

Check the indentation of lines inside the loop.

Python requires code inside loops to be indented. Here print and i += 1 are not indented, causing IndentationError.

🚀 Application

expert

Determine final value after nested loops

What is the final value of total after running this code?

total = 0
for x in range(3):
    for y in range(2):
        total += x + y

A 18

B 12

C 9

D 15

💡 Hint

Calculate sums for each pair (x, y) and add carefully.

Pairs and sums: (0+0)=0, (0+1)=1, (1+0)=1, (1+1)=2, (2+0)=2, (2+1)=3. Sum = 0+1+1+2+2+3 = 9.