Constants and literals in C++ - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to declare a constant integer named MAX with value 100.

C++

const int MAX = [1];

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

A100

B10.0

Cmax

D"100"

Attempts:

3 left

💡 Hint

Common Mistakes

Using quotes around numbers, which makes them strings.

Using a variable name instead of a literal value.

The constant integer MAX is assigned the literal value 100 without quotes.

2fill in blank

medium

Complete the code to declare a constant floating-point number PI with value 3.14.

C++

const double PI = [1];

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

A3.14

B3,14

C"3.14"

Dpi

Attempts:

3 left

💡 Hint

Common Mistakes

Using a comma instead of a dot for decimals.

Putting the number inside quotes, making it a string.

The constant PI is assigned the floating-point literal 3.14 using a dot as decimal separator.

3fill in blank

hard

Fix the error in the code to declare a constant character named LETTER with value 'A'.

C++

const char LETTER = [1];

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

Aletter

B"A"

CA

D'A'

Attempts:

3 left

💡 Hint

Common Mistakes

Using double quotes which create string literals.

Using unquoted letters which cause errors.

Character literals use single quotes in C++.

4fill in blank

hard

Complete the code to declare a constant boolean named IS_READY with value true.

C++

const bool IS_READY = [1];

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

A"true"

Btrue

Cfalse

DTrue

Attempts:

3 left

💡 Hint

Common Mistakes

Using capitalized True which is invalid in C++.

Using quotes which make it a string.

Boolean constants use lowercase true or false without quotes in C++.

5fill in blank

hard

Complete the code to declare a constant string named GREETING with value "Hello".

C++

const std::string GREETING = [1];

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

AHello

B'Hello'

C"Hello"

Dstd::string("Hello")

Attempts:

3 left

💡 Hint

Common Mistakes

Using single quotes which are for characters.

Using unquoted words which cause errors.

String literals in C++ are enclosed in double quotes. Using std::string constructor is also valid but here the literal is expected.

Practice

1. Which of the following best describes a constant in C++?

easy

A. A fixed value that cannot be changed after initialization

B. A variable that can change its value anytime

C. A function that returns a fixed value

D. A pointer to a variable

Solution

1. Step 1: Understand the meaning of constant

   A constant in C++ is a value that once set cannot be changed during program execution.

2. Step 2: Compare options with definition

   A fixed value that cannot be changed after initialization matches this definition exactly, while others describe variables or functions.

3. Final Answer:

   A fixed value that cannot be changed after initialization -> Option A

4. Quick Check:

   Constant = fixed value [OK]

Hint: Constants never change value after being set [OK]

Common Mistakes:

• Confusing constants with variables
• Thinking constants are functions
• Assuming pointers are constants

2. Which of the following is the correct way to declare a constant integer named MAX_SIZE with value 100 in C++?

easy

A. int MAX_SIZE = 100;

B. constant int MAX_SIZE = 100;

C. int const MAX_SIZE;

D. const int MAX_SIZE = 100;

Solution

1. Step 1: Recall syntax for constant declaration

   In C++, the keyword const before the type declares a constant.

2. Step 2: Check each option

   const int MAX_SIZE = 100; uses const int MAX_SIZE = 100; which is correct. int MAX_SIZE = 100; misses const, C is incomplete without initialization, D uses invalid keyword.

3. Final Answer:

   const int MAX_SIZE = 100; -> Option D

4. Quick Check:

   Use const before type for constants [OK]

Hint: Use 'const' keyword before type to declare constants [OK]

Common Mistakes:

• Omitting 'const' keyword
• Using 'constant' instead of 'const'
• Not initializing the constant

3. What is the output of the following C++ code?

const int x = 5;
int y = 10;
std::cout << x + y << std::endl;

medium

A. Runtime error

B. 15

C. Syntax error

D. 510

Solution

1. Step 1: Understand the code variables

   Variable x is a constant with value 5, y is 10.

2. Step 2: Calculate the expression output

   The expression x + y equals 5 + 10 = 15, which is printed.

3. Final Answer:

   15 -> Option B

4. Quick Check:

   5 + 10 = 15 [OK]

Hint: Add constant and variable values normally [OK]

Common Mistakes:

• Thinking constants cause errors
• Concatenating numbers as strings
• Expecting runtime errors

4. Identify the error in the following C++ code:

const int a = 10;
a = 20;
std::cout << a << std::endl;

medium

A. Incorrect use of std::cout

B. Missing semicolon after declaration

C. Cannot assign a new value to a constant variable

D. Variable 'a' not declared

Solution

1. Step 1: Analyze constant assignment

   The variable a is declared as constant with value 10.

2. Step 2: Check reassignment

   Trying to assign 20 to a is illegal because constants cannot change value.

3. Final Answer:

   Cannot assign a new value to a constant variable -> Option C

4. Quick Check:

   Constants cannot be reassigned [OK]

Hint: Constants cannot be changed after initialization [OK]

Common Mistakes:

• Trying to reassign constants
• Ignoring compiler error messages
• Confusing constants with variables

5. You want to define a constant literal for the value of pi (3.14159) that cannot be changed and can be used throughout your program. Which of the following is the best way to do this in C++?

hard

A. const double pi = 3.14159;

B. #define pi 3.14159

C. float pi = 3.14159;

D. double const pi;

Solution

1. Step 1: Understand constant literal requirements

   The value should be fixed, unchangeable, and precise (double is better than float).

2. Step 2: Evaluate options

   const double pi = 3.14159; declares a constant double with initialization, which is best practice. float pi = 3.14159; is not constant, C uses macro which is less safe, D misses initialization.

3. Final Answer:

   const double pi = 3.14159; -> Option A

4. Quick Check:

   Use 'const double' with initialization for constants [OK]

Hint: Use 'const double' with value for precise constants [OK]

Common Mistakes:

• Using non-const variables for constants
• Using #define instead of const
• Not initializing constants