Type modifiers in C++ - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to declare a constant integer variable named num with value 10.

C++

const [1] num = 10;

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

Aint

Bfloat

Cchar

Ddouble

Attempts:

3 left

💡 Hint

Common Mistakes

Using a floating-point type like float or double instead of int.

Forgetting to add const before the type.

The const keyword makes the variable num constant, and int declares it as an integer type.

2fill in blank

medium

Complete the code to declare a pointer to a constant character named ptr.

C++

const char* [1];

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

AcharPtr

BpChar

Cpointer

Dptr

Attempts:

3 left

💡 Hint

Common Mistakes

Using a variable name different from ptr as asked.

Placing the asterisk incorrectly.

The variable name ptr is used as the pointer to a constant character.

3fill in blank

hard

Fix the error in the code by completing the type modifier to declare a volatile integer variable named counter.

C++

[1] int counter;

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

Aconstant

Bmutable

Cvolatile

Dstatic

Attempts:

3 left

💡 Hint

Common Mistakes

Using constant instead of volatile.

Using static which has a different meaning.

The volatile keyword tells the compiler that the variable counter can be changed unexpectedly, so it should not optimize it away.

4fill in blank

hard

Fill both blanks to declare a pointer to a volatile integer named p.

C++

[1] int [2] p;

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

Avolatile

B*

C&

Dconst

Attempts:

3 left

💡 Hint

Common Mistakes

Using & instead of * for pointer declaration.

Placing const instead of volatile.

The keyword volatile modifies the integer type, and * declares p as a pointer.

5fill in blank

hard

Fill all three blanks to declare a constant pointer to a constant integer named ptr.

C++

[1] int [2] [3] ptr;

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

Aconst

B*

Dvolatile

Attempts:

3 left

💡 Hint

Common Mistakes

Forgetting the second const to make the pointer constant.

Using volatile instead of const.

The first const makes the integer constant, the * declares a pointer, and the second const makes the pointer itself constant.

Practice

1. Which of the following type modifiers in C++ makes a variable value unchangeable after initialization?

easy

A. long

B. unsigned

C. volatile

D. const

Solution

1. Step 1: Understand the role of const

   The const modifier makes a variable's value fixed after it is set.

2. Step 2: Compare with other modifiers

   unsigned changes number sign, volatile affects optimization, long changes size, but none prevent value change.

3. Final Answer:

   const -> Option D

4. Quick Check:

   const = unchangeable value [OK]

Hint: const means value cannot be changed after set [OK]

Common Mistakes:

• Confusing const with unsigned
• Thinking volatile prevents changes
• Assuming long affects constness

2. Which of the following declarations correctly uses the unsigned modifier for an integer variable named count?

easy

A. unsigned count int;

B. count unsigned int;

C. unsigned int count;

D. int count unsigned;

Solution

1. Step 1: Recall correct syntax for unsigned int

   The correct order is unsigned int followed by the variable name.

2. Step 2: Check each option

   unsigned count int; invalid order; count unsigned int; places variable before type, invalid; unsigned int count; correct; int count unsigned; invalid.

3. Final Answer:

   unsigned int count; -> Option C

4. Quick Check:

   unsigned int before variable name [OK]

Hint: Put unsigned before int and then variable name [OK]

Common Mistakes:

• Placing unsigned after variable name
• Mixing order of type and modifier
• Using invalid syntax like unsigned count int

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

unsigned int x = 10;
int y = -5;
if (x + y > 5)
    std::cout << "True";
else
    std::cout << "False";

medium

A. True

B. False

C. Compilation error

D. Undefined behavior

Solution

1. Step 1: Understand unsigned and signed addition

   Adding signed -5 to unsigned 10: -5 promotes to unsigned (large value, e.g., 4294967291u on 32-bit).

2. Step 2: Calculate the result and compare

   10u + 4294967291u = 4294967286u (wraps around mod 2^32). 4294967286u > 5u is true, so prints "True".

3. Final Answer:

   True -> Option A

4. Quick Check:

   unsigned + negative int promotes and wraps to large unsigned > 5 true [OK]

Hint: Mixing unsigned + signed negative promotes and wraps around [OK]

Common Mistakes:

• Assuming -5 stays negative (ignores promotion)
• Expecting True (ignores wraparound)
• Thinking this causes compile error

4. Identify the error in this code snippet:

const int x;
x = 5;

medium

A. Missing initialization of const variable

B. Incorrect use of int type

C. Assignment operator is wrong

D. No error, code is correct

Solution

1. Step 1: Check const variable initialization rules

   A const variable must be initialized when declared.

2. Step 2: Analyze the code

   Here, const int x; is declared without initialization, then assigned later, which is invalid.

3. Final Answer:

   Missing initialization of const variable -> Option A

4. Quick Check:

   const must be initialized immediately [OK]

Hint: const variables need immediate initialization [OK]

Common Mistakes:

• Trying to assign const after declaration
• Ignoring initialization requirement
• Thinking assignment operator is wrong

5. You want to store a large positive number that can never be negative and might exceed 2 billion. Which type modifier combination is best for the variable score?

hard

A. const int score;

B. unsigned long score;

C. short unsigned score;

D. volatile int score;

Solution

1. Step 1: Understand the data requirements

   We need a large positive number, no negatives, possibly > 2 billion.

2. Step 2: Match type modifiers to needs

   unsigned ensures no negatives; long increases size to hold large values; const fixes value; short limits size; volatile affects optimization, not size.

3. Step 3: Choose best option

   unsigned long fits the need best.

4. Final Answer:

   unsigned long score; -> Option B

5. Quick Check:

   unsigned long = large positive number [OK]

Hint: Use unsigned long for large positive numbers [OK]

Common Mistakes:

• Choosing const which fixes value
• Using short which limits size
• Using volatile which doesn't affect size