Constants and literals - 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'

Aint

B100

CMAX

Dconst

Attempts:

3 left

💡 Hint

Common Mistakes

Using variable name instead of value

Forgetting to assign a value

The constant MAX is assigned the literal value 100.

2fill in blank

medium

Complete the code to assign the character literal 'A' to the variable letter.

C

char letter = [1];

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

A'A'

B"a"

CA

D"A"

Attempts:

3 left

💡 Hint

Common Mistakes

Using double quotes for characters

Omitting quotes around the character

Character literals in C use single quotes, like 'A'.

3fill in blank

hard

Fix the error in the code by completing the constant declaration for PI with value 3.14.

C

const float PI = [1];

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

A3,14

B"3.14"

C3.14f

D3.14

Attempts:

3 left

💡 Hint

Common Mistakes

Using comma instead of dot for decimals

Using string literal instead of numeric literal

Float literals should have an 'f' suffix to specify float type in C.

4fill in blank

hard

Fill both blanks to create a constant double named gravity with value 9.8.

C

const [1] gravity = [2];

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

Adouble

Bfloat

C9.8

D9.8f

Attempts:

3 left

💡 Hint

Common Mistakes

Using float type instead of double

Adding 'f' suffix to double literal

Use 'double' type for gravity and assign the literal 9.8 without suffix.

5fill in blank

hard

Fill all three blanks to declare a constant string pointer named greeting with value "Hello".

C

const [1] [2] = [3];

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

Achar

B*

C"Hello"

Dstring

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'string' type which is not standard in C

Missing pointer symbol '*' for string pointer

Strings in C are char pointers. Use 'const char * greeting = "Hello";'.

Practice

1. What is a constant in C programming?

easy

A. A function that returns a value

B. A fixed value that cannot be changed during program execution

C. A variable that can change its value anytime

D. A type of loop in C

Solution

1. Step 1: Understand the meaning of constant

   A constant is a value that remains the same throughout the program and cannot be modified.

2. Step 2: Compare options with definition

   Only A fixed value that cannot be changed during program execution describes a fixed value that does not change, which matches the definition of a constant.

3. Final Answer:

   A fixed value that cannot be changed during program execution -> Option B

4. Quick Check:

   Constant = fixed value [OK]

Hint: Constants never change value once set [OK]

Common Mistakes:

• Confusing constants with variables
• Thinking constants are functions
• Mixing constants with loops

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

easy

A. All of the above

B. #define MAX 100

C. const int MAX = 100;

D. int const MAX = 100;

Solution

1. Step 1: Review ways to define constants in C

   Constants can be defined using #define or using const keyword with variable declaration.

2. Step 2: Check each option

   #define MAX 100 uses #define, which is valid. int const MAX = 100; uses int const, which is valid. const int MAX = 100; uses const int, also valid. So all are correct.

3. Final Answer:

   All of the above -> Option A

4. Quick Check:

   All methods define constants [OK]

Hint: Use #define or const keyword for constants [OK]

Common Mistakes:

• Using variable without const
• Missing semicolon in const declaration
• Confusing #define with variable

3. What will be the output of the following C code?

#include <stdio.h>
#define PI 3.14
int main() {
    const int radius = 5;
    float area = PI * radius * radius;
    printf("%.2f", area);
    return 0;
}

medium

A. Syntax error

B. 31.40

C. 78.50

D. 25.00

Solution

1. Step 1: Calculate area using given formula

   Area = PI * radius * radius = 3.14 * 5 * 5 = 3.14 * 25 = 78.5

2. Step 2: Check printf formatting

   Using %.2f prints the float with 2 decimal places, so output is 78.50

3. Final Answer:

   78.50 -> Option C

4. Quick Check:

   Area = 3.14 * 25 = 78.50 [OK]

Hint: Calculate formula carefully and check decimal format [OK]

Common Mistakes:

• Using wrong formula
• Ignoring decimal places
• Confusing radius with diameter

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

const int x;
x = 10;
printf("%d", x);

medium

A. Cannot assign value to const variable after declaration

B. Missing semicolon after declaration

C. printf format specifier is wrong

D. No error, code runs fine

Solution

1. Step 1: Understand const variable rules

   A const variable must be initialized when declared and cannot be assigned a value later.

2. Step 2: Analyze the code

   Here, const int x; declares x without initialization, then tries to assign 10 later, which is not allowed.

3. Final Answer:

   Cannot assign value to const variable after declaration -> Option A

4. Quick Check:

   const variables must be initialized once [OK]

Hint: Initialize const variables when declared [OK]

Common Mistakes:

• Assigning value after declaration
• Not initializing const variables
• Ignoring const rules

5. You want to create a constant array of 3 integers in C that cannot be modified after initialization. Which of the following declarations achieves this correctly?

hard

A. int arr[3] = {1, 2, 3};

B. int const *arr = {1, 2, 3};

C. #define arr {1, 2, 3}

D. const int arr[3] = {1, 2, 3};

Solution

1. Step 1: Understand const array declaration

   Declaring an array with const int arr[3] means the elements cannot be changed after initialization.

2. Step 2: Check each option

   int arr[3] = {1, 2, 3}; declares a normal array, elements can be changed. const int arr[3] = {1, 2, 3}; declares a constant array correctly. #define arr {1, 2, 3} uses #define incorrectly for array. int const *arr = {1, 2, 3}; declares a pointer to const int, but initialization is invalid.

3. Final Answer:

   const int arr[3] = {1, 2, 3}; -> Option D

4. Quick Check:

   const array elements cannot change [OK]

Hint: Use const before type for constant arrays [OK]

Common Mistakes:

• Using #define for arrays
• Declaring non-const arrays
• Incorrect pointer initialization