Data types (int, double, String, bool) in Flutter - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ ui_behavior

intermediate

What will this Flutter Text widget display?

Consider this Flutter code snippet:

int count = 5;
double price = 3.5;
String label = 'Total';
bool isActive = true;

Text('$label: \$${count * price} - Active: $isActive')

What text will appear on the screen?

Flutter

int count = 5;
double price = 3.5;
String label = 'Total';
bool isActive = true;

Text('$label: \$${count * price} - Active: $isActive')

A Total: 17.5 - Active: false

B Total: 17.5 - Active: true

C Total: $17.5 - Active: true

D Total: $17.5 - Active: false

💡 Hint

Remember that \$ inside a string escapes the dollar sign to show it literally.

The string uses \$ to show the dollar sign literally, then ${count * price} calculates 5 * 3.5 = 17.5. The bool isActive is true, so the full text is 'Total: $17.5 - Active: true'.

📝 Syntax

intermediate

Which option correctly declares a double variable in Dart?

You want to store a decimal number in a variable named price. Which declaration is correct?

A double price = 9.99;

B int price = 9.99;

C String price = 9.99;

D bool price = 9.99;

💡 Hint

Decimals need a type that supports fractional numbers.

double is the correct type for decimal numbers. int only stores whole numbers. String stores text. bool stores true/false.

🧠 Conceptual

advanced

What is the result of this Dart expression?

Given:

int a = 3;
double b = 2.0;
bool c = (a > b);

What is the value of c?

Flutter

int a = 3;
double b = 2.0;
bool c = (a > b);

A 3.0

B true

C TypeError

D false

💡 Hint

Compare 3 and 2.0 using > operator.

3 is greater than 2.0, so (a > b) is true. The bool c stores true.

🔧 Debug

advanced

Why does this Dart code cause an error?

Look at this code:

int x = 5;
String y = x + 3;

Why does it cause an error?

Flutter

int x = 5;
String y = x + 3;

A You cannot assign int to String without conversion.

B Variables must be declared with var keyword.

C You cannot add int to int and assign to String directly.

D The + operator is not defined for int types.

💡 Hint

Check the types on both sides of the assignment.

x + 3 is an int (5 + 3 = 8). You cannot assign an int directly to a String variable without converting it to a string.

❓ lifecycle

expert

What happens if you try to change a final int variable in Flutter?

Consider this code:

final int count = 10;
count = 15;

What will happen when you run this code?

Flutter

final int count = 10;
count = 15;

A The value of count changes to 15 at runtime.

B No error, count becomes 15.

C Runtime error: Variable 'count' is immutable.

D Compile-time error: Cannot assign to final variable 'count'.

💡 Hint

final variables cannot be reassigned after initialization.

final means the variable can only be set once. Trying to assign a new value causes a compile-time error.

Practice

1. Which data type in Flutter is used to store true or false values?

easy

A. bool

B. int

C. String

D. double

Solution

1. Step 1: Understand the bool data type

   The bool data type stores only two values: true or false.

2. Step 2: Compare with other data types

   int stores whole numbers, double stores decimals, and String stores text, so they do not fit true/false values.

3. Final Answer:

   bool -> Option A

4. Quick Check:

   bool = true or false [OK]

Hint: Remember: bool means true or false only [OK]

Common Mistakes:

• Confusing bool with int
• Thinking String can store true/false
• Using double for true/false

2. Which of the following is the correct way to declare a double variable named price with value 9.99 in Flutter?

easy

A. double price = 9,99;

B. double price = 9.99;

C. int price = 9.99;

D. String price = 9.99;

Solution

1. Step 1: Check the syntax for double declaration

   In Flutter, double values use a dot (.) as decimal separator, so 9.99 is correct.

2. Step 2: Verify variable type and value match

   double price = 9.99; is correct. double price = 9,99; uses comma which is invalid. int price = 9.99; uses int for decimal value. String price = 9.99; uses String but value is numeric.

3. Final Answer:

   double price = 9.99; -> Option B

4. Quick Check:

   double uses dot for decimals [OK]

Hint: Use dot (.) for decimals in double, not comma [OK]

Common Mistakes:

• Using comma instead of dot
• Assigning decimal to int
• Assigning number to String without quotes

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

int a = 5;
double b = 2.0;
print(a + b);

medium

A. 7.0

B. 7.00

C. 7

D. Error

Solution

1. Step 1: Understand type promotion in addition

   Adding int and double results in a double value in Flutter.

2. Step 2: Calculate the sum

   5 + 2.0 = 7.0 as a double, so print outputs 7.0.

3. Final Answer:

   7.0 -> Option A

4. Quick Check:

   int + double = double [OK]

Hint: int + double results in double output [OK]

Common Mistakes:

• Expecting int output
• Thinking print shows 7.00
• Assuming syntax error

4. Identify the error in this Flutter code snippet:

bool isActive = "true";

medium

A. Variable name is invalid

B. Missing semicolon

C. bool cannot store text in quotes

D. No error, code is correct

Solution

1. Step 1: Check bool assignment rules

   bool variables must be assigned true or false without quotes.

2. Step 2: Analyze the code

   "true" is a String, not a bool, so this causes a type error.

3. Final Answer:

   bool cannot store text in quotes -> Option C

4. Quick Check:

   bool = true or false without quotes [OK]

Hint: Assign bool without quotes, quotes mean String [OK]

Common Mistakes:

• Using quotes around true/false
• Ignoring type mismatch errors
• Assuming variable name causes error

5. You want to store a user's age, height in meters, name, and whether they are a student. Which Flutter data types should you use for age, height, name, and isStudent respectively?

hard

A. bool, String, double, int

B. double, int, bool, String

C. String, double, int, bool

D. int, double, String, bool

Solution

1. Step 1: Match each variable to its data type

   Age is a whole number -> int; height is decimal -> double; name is text -> String; isStudent is true/false -> bool.

2. Step 2: Verify option matches all types correctly

   int, double, String, bool matches int, double, String, bool in order for age, height, name, isStudent.

3. Final Answer:

   int, double, String, bool -> Option D

4. Quick Check:

   Whole number, decimal, text, true/false [OK]

Hint: Match data type to real-world meaning: number, decimal, text, true/false [OK]

Common Mistakes:

• Mixing int and double
• Using bool for text
• Confusing order of types