Control flow (if, for, while, switch) in Flutter - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to check if a number is positive.

Flutter

if (number [1] 0) {
  print('Positive');
}

Drag options to blanks, or click blank then click option'

A<

B==

C>

D<=

Attempts:

3 left

💡 Hint

Common Mistakes

Using '<' instead of '>' causes wrong logic.

Using '==' checks only for zero.

The condition should check if the number is greater than zero to be positive.

2fill in blank

medium

Complete the for loop to print numbers from 0 to 4.

Flutter

for (int i = 0; i [1] 5; i++) {
  print(i);
}

Drag options to blanks, or click blank then click option'

A<

B>

C>=

D<=

Attempts:

3 left

💡 Hint

Common Mistakes

Using '<=' prints 0 to 5, which is one extra.

Using '>' causes the loop to never run.

The loop should run while i is less than 5 to print 0 to 4.

3fill in blank

hard

Fix the error in the while loop condition to stop at 3.

Flutter

int count = 0;
while (count [1] 3) {
  print(count);
  count++;
}

Drag options to blanks, or click blank then click option'

A<

B<=

C>=

D>

Attempts:

3 left

💡 Hint

Common Mistakes

Using '<' excludes 3 from the loop.

Using '>' causes the loop to never run.

The loop should run while count is less than or equal to 3 to include 3.

4fill in blank

hard

Fill both blanks to create a for loop that prints even numbers from 2 to 6.

Flutter

for (int i = [1]; i [2] 6; i += 2) {
  print(i);
}

Drag options to blanks, or click blank then click option'

A2

B<

C<=

D1

Attempts:

3 left

💡 Hint

Common Mistakes

Using '<' excludes 6 from printing.

Starting at 1 prints odd numbers.

The loop starts at 2 and runs while i is less than or equal to 6 to include 6.

5fill in blank

hard

Fill all three blanks to create a switch statement that prints the day name for 1, 2, or 3.

Flutter

switch(day) {
  case [1]:
    print('Monday');
    break;
  case [2]:
    print('Tuesday');
    break;
  case [3]:
    print('Wednesday');
    break;
  default:
    print('Invalid day');
}

Drag options to blanks, or click blank then click option'

A1

B2

C3

D4

Attempts:

3 left

💡 Hint

Common Mistakes

Using 4 causes the default case to run.

Mixing numbers changes the output.

The cases should match the day numbers 1, 2, and 3 for Monday, Tuesday, and Wednesday.

Practice

1. Which control flow statement in Flutter is used to make decisions based on conditions?

easy

A. if

B. for

C. while

D. switch

Solution

1. Step 1: Understand the purpose of control flow statements

   if statements let the app choose between actions based on conditions.

2. Step 2: Identify the decision-making statement

   Among the options, only if directly tests a condition to decide what code runs.

3. Final Answer:

   if -> Option A

4. Quick Check:

   Decision making = if [OK]

Hint: Use if to check conditions and decide [OK]

Common Mistakes:

• Confusing for loops with decision making
• Thinking while is for choices instead of repetition
• Assuming switch is the only decision tool

2. Which of the following is the correct syntax for a for loop in Flutter to print numbers 0 to 4?

easy

A. for (int i = 1; i < 5; i++) { print(i); }

B. for i in 0 to 4 { print(i); }

C. for (int i = 0; i < 5; i++) { print(i); }

D. for (i = 0; i <= 5; i++) print(i);

Solution

1. Step 1: Check the loop initialization and condition

   for (int i = 0; i < 5; i++) { print(i); } initializes i at 0 and loops while i < 5, which prints 0 to 4.

2. Step 2: Verify syntax correctness

   for (int i = 0; i < 5; i++) { print(i); } uses correct Dart syntax with types and braces.

3. Final Answer:

   for (int i = 0; i < 5; i++) { print(i); } -> Option C

4. Quick Check:

   Correct Dart for loop syntax = for (int i = 0; i < 5; i++) { print(i); } [OK]

Hint: Remember Dart for loops use semicolons and braces [OK]

Common Mistakes:

• Using Python-style loops like 'for i in 0 to 4'
• Off-by-one errors in loop conditions
• Missing type declaration for loop variable

3. What will be the output of this Flutter Dart code?

int count = 0;
while (count < 3) {
  print(count);
  count++;
}

medium

A. 1 2 3

B. No output

C. 0 1 2 3

D. 0 1 2

Solution

1. Step 1: Analyze the while loop condition and increments

   The loop starts with count = 0 and runs while count < 3, printing count each time.

2. Step 2: Trace the printed values

   It prints 0, then increments to 1, prints 1, increments to 2, prints 2, increments to 3, then stops.

3. Final Answer:

   0 1 2 -> Option D

4. Quick Check:

   Loop prints values less than 3 = 0 1 2 [OK]

Hint: Count starts at 0 and stops before 3, so prints 0,1,2 [OK]

Common Mistakes:

• Including 3 in output mistakenly
• Confusing post-increment behavior
• Thinking loop runs zero times

4. Identify the error in this Flutter Dart code snippet:

int i = 0;
while (i < 5) {
  print(i);
}

medium

A. Missing increment of i inside the loop

B. Incorrect while loop syntax

C. Variable i should be declared inside the loop

D. print() cannot be used inside loops

Solution

1. Step 1: Check loop control variables

   The variable i is initialized but never changed inside the loop.

2. Step 2: Understand loop behavior

   Without incrementing i, the condition i < 5 is always true, causing an infinite loop.

3. Final Answer:

   Missing increment of i inside the loop -> Option A

4. Quick Check:

   Loops need changing variables to stop [OK]

Hint: Always update loop variables to avoid infinite loops [OK]

Common Mistakes:

• Forgetting to increment loop counters
• Assuming loop ends automatically
• Misunderstanding while loop syntax

5. You want to display a message in Flutter based on a user's score:

int score = 75;
switch (score ~/ 10) {
  case 10:
  case 9:
    print('Excellent');
    break;
  case 8:
    print('Very Good');
    break;
  case 7:
    print('Good');
    break;
  default:
    print('Keep Trying');
}

What message will be printed?

hard

A. Excellent

B. Good

C. Very Good

D. Keep Trying

Solution

1. Step 1: Calculate the switch expression value

   score is 75, so score ~/ 10 is integer division 75/10 = 7.

2. Step 2: Match the case for value 7

   Case 7 matches and prints 'Good'.

3. Final Answer:

   Good -> Option B

4. Quick Check:

   Integer division selects case 7 = 'Good' [OK]

Hint: Use integer division to group scores in switch cases [OK]

Common Mistakes:

• Forgetting integer division operator ~/
• Assuming score matches case directly
• Missing break statements causing fall-through