Register storage class - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to declare a register variable named count.

C

register [1] count;

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 for a simple counter.

Forgetting to specify the data type after the register keyword.

The register keyword is used to declare a variable that should be stored in a CPU register for faster access. Here, int is the correct type for the variable count.

2fill in blank

medium

Complete the code to declare a register variable named speed of type float.

C

register [1] speed;

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

Aint

Bfloat

Cchar

Ddouble

Attempts:

3 left

💡 Hint

Common Mistakes

Using int instead of float for decimal values.

Omitting the data type after the register keyword.

The variable speed is declared as a float type with the register storage class for faster access.

3fill in blank

hard

Fix the error in the code by completing the declaration of a register variable named flag.

C

register [1] flag;

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

Achar

Bfloat

Cint

Dvoid

Attempts:

3 left

💡 Hint

Common Mistakes

Using void which is not a valid variable type.

Using float unnecessarily for a flag variable.

The variable flag is typically a character or small integer. Here, char is the correct type to use with register.

4fill in blank

hard

Fill both blanks to declare a register variable named index of type unsigned int.

C

register [1] [2] index;

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

Aunsigned

Bint

Clong

Dshort

Attempts:

3 left

💡 Hint

Common Mistakes

Using long or short instead of int.

Omitting either unsigned or int.

The correct declaration for an unsigned integer register variable is register unsigned int index;.

5fill in blank

hard

Fill all three blanks to declare a register variable named totalCount of type long long int.

C

register [1] [2] [3] totalCount;

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

Along

Bint

Dunsigned

Attempts:

3 left

💡 Hint

Common Mistakes

Using unsigned when not required.

Incorrect order of type specifiers.

The correct declaration for a long long int register variable is register long long int totalCount;.

Practice

1. What is the main purpose of the register storage class in C?

easy

A. To suggest storing the variable in CPU registers for faster access

B. To allocate memory on the heap

C. To make the variable global

D. To allow the variable to be accessed outside the function

Solution

1. Step 1: Understand the role of register keyword

   The register keyword suggests to the compiler that the variable should be stored in CPU registers for faster access.

2. Step 2: Compare with other storage classes

   Unlike global or heap variables, register variables are local and optimized for speed, not for scope or memory allocation.

3. Final Answer:

   To suggest storing the variable in CPU registers for faster access -> Option A

4. Quick Check:

   register means fast access [OK]

Hint: Remember: register means fast access in CPU registers [OK]

Common Mistakes:

• Thinking register allocates memory on the heap
• Assuming register variables are global
• Believing register variables can be accessed outside functions

2. Which of the following is the correct syntax to declare a register variable in C?

easy

A. int count register;

B. int register count;

C. register = int count;

D. register int count;

Solution

1. Step 1: Recall correct syntax for register declaration

   The correct syntax places the keyword register before the type: register int count;.

2. Step 2: Check other options for syntax errors

   Options A, B, and C have incorrect order or invalid assignment syntax.

3. Final Answer:

   register int count; -> Option D

4. Quick Check:

   Keyword before type = correct syntax [OK]

Hint: Put 'register' before the type name [OK]

Common Mistakes:

• Placing 'register' after the variable name
• Using assignment '=' in declaration
• Mixing order of type and storage class

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

void func() {
    register int x = 5;
    // printf("%p", &x); // Uncommenting this line causes error
    printf("%d", x);
}
int main() {
    func();
    return 0;
}

medium

A. Garbage value

B. Compilation error due to &x

C. 5

D. Runtime error

Solution

1. Step 1: Understand register variable usage

   The variable x is declared as register int, so it cannot have its address taken.

2. Step 2: Analyze the code behavior

   The commented line with &x would cause a compilation error if uncommented. But as is, the code prints the value of x, which is 5.

3. Final Answer:

   5 -> Option C

4. Quick Check:

   Printing register variable value works fine [OK]

Hint: Register variables can't use & but can print value [OK]

Common Mistakes:

• Trying to print address of register variable
• Expecting runtime error instead of compile error
• Confusing garbage value with initialized value

4. Identify the error in the following code snippet:

void example() {
    register int a = 10;
    int *p = &a;
    printf("%d", *p);
}

medium

A. Register variable cannot be initialized

B. Cannot take address of register variable

C. Pointer declaration is invalid

D. No error, code runs fine

Solution

1. Step 1: Check usage of register variable

   The variable a is declared as register int, so its address cannot be taken.

2. Step 2: Identify the error in pointer assignment

   The line int *p = &a; tries to take the address of a register variable, which causes a compilation error.

3. Final Answer:

   Cannot take address of register variable -> Option B

4. Quick Check:

   Address of register variable forbidden [OK]

Hint: Register variables have no address, so & operator causes error [OK]

Common Mistakes:

• Thinking register variables can't be initialized
• Assuming pointer declaration is wrong
• Believing code runs without error

5. Consider this code snippet:

void count() {
    register int i;
    for(i = 0; i < 3; i++) {
        printf("%d ", i);
    }
}
int main() {
    count();
    return 0;
}

What is the main advantage of using register for variable i here?

hard

A. It suggests faster access to i since it is frequently used

B. It allows taking the address of i inside the loop

C. It makes i a global variable

D. It automatically initializes i to zero

Solution

1. Step 1: Analyze the role of register in loops

   Loop variables like i are used repeatedly, so storing them in CPU registers speeds up access.

2. Step 2: Check other options for correctness

   It allows taking the address of i inside the loop is wrong because you cannot take the address of a register variable. It makes i a global variable is wrong because i is local, not global. It automatically initializes i to zero is wrong because register does not initialize variables.

3. Final Answer:

   It suggests faster access to i since it is frequently used -> Option A

4. Quick Check:

   Register = fast access for frequent vars [OK]

Hint: Register speeds up frequent variable access like loop counters [OK]

Common Mistakes:

• Thinking register allows & operator
• Assuming register makes variable global
• Believing register initializes variables automatically