Why storage classes are needed - Test Your Understanding

Practice - 5 Tasks

1fill in blank

easy

Complete the code to declare a variable with automatic storage class.

C

void function() {
    [1] int x = 10;
}

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

Astatic

Bauto

Cextern

Dregister

Attempts:

3 left

💡 Hint

Common Mistakes

Using static instead of auto inside functions.

The auto keyword declares a variable with automatic storage, which is the default inside functions.

2fill in blank

medium

Complete the code to declare a variable with static storage class inside a function.

C

void counter() {
    [1] int count = 0;
    count++;
    printf("%d", count);
}

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

Aauto

Bregister

Cextern

Dstatic

Attempts:

3 left

💡 Hint

Common Mistakes

Using auto which resets the variable each call.

The static keyword inside a function makes the variable keep its value between calls.

3fill in blank

hard

Fix the error in the code by choosing the correct storage class for a global variable.

C

[1] int global_var = 5;

void func() {
    printf("%d", global_var);
}

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

Aextern

Bauto

Cstatic

Dregister

Attempts:

3 left

💡 Hint

Common Mistakes

Using extern which declares a variable defined elsewhere.

Using static for a global variable limits its scope to the file, which is often needed to avoid conflicts.

4fill in blank

hard

Fill both blanks to declare an external variable and use it in another file.

C

// file1.c
[1] int shared_var = 100;

// file2.c
[2] int shared_var;

void print_var() {
    printf("%d", shared_var);
}

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

Aextern

Bstatic

Cauto

Dregister

Attempts:

3 left

💡 Hint

Common Mistakes

Using static in both files which hides the variable.

In file1.c, static limits the variable to that file, so it should be removed to share it. The correct is to declare normally (no static) in file1.c and extern in file2.c to access it.

5fill in blank

hard

Fill all three blanks to declare a register variable, use it in a loop, and print its value.

C

void loop() {
    [1] int i;
    for (i = 0; i [2] 5; i++) {
        printf("%d ", i);
    }
    printf("\nValue of i: %d", [3]);
}

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

Aregister

B<

Ci

Dstatic

Attempts:

3 left

💡 Hint

Common Mistakes

Using static inside the loop which changes variable lifetime.

register suggests storing the variable in a CPU register for faster access. The loop runs while i < 5, and printing i shows its final value.

Practice

1. Why are storage classes needed in C programming?

easy

A. To allocate memory dynamically

B. To define the data type of variables

C. To perform arithmetic operations

D. To control the lifetime and visibility of variables

Solution

1. Step 1: Understand the role of storage classes

   Storage classes in C define how long a variable exists and where it can be accessed.

2. Step 2: Differentiate from other concepts

   Data types define variable type, arithmetic operations perform calculations, and dynamic memory allocation is separate from storage classes.

3. Final Answer:

   To control the lifetime and visibility of variables -> Option D

4. Quick Check:

   Storage classes = control lifetime and visibility [OK]

Hint: Storage classes manage variable life and access [OK]

Common Mistakes:

• Confusing storage classes with data types
• Thinking storage classes allocate memory dynamically
• Assuming storage classes perform operations

2. Which of the following is the correct syntax to declare a variable with static storage class in C?

easy

A. count static int;

B. static int count;

C. int static count;

D. int count static;

Solution

1. Step 1: Recall correct order of storage class declaration

   In C, the storage class specifier comes before the data type.

2. Step 2: Verify each option's syntax

   static int count; uses 'static int count;' which is correct. Other options place 'static' incorrectly.

3. Final Answer:

   static int count; -> Option B

4. Quick Check:

   Storage class before type = correct syntax [OK]

Hint: Storage class keyword always precedes data type [OK]

Common Mistakes:

• Placing storage class after variable name
• Mixing order of keywords
• Using invalid syntax like 'count static int;'

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

void func() {
    static int count = 0;
    count++;
    printf("%d ", count);
}

int main() {
    for(int i = 0; i < 3; i++) {
        func();
    }
    return 0;
}

medium

A. 1 2 3

B. 3 3 3

C. 0 1 2

D. 1 1 1

Solution

1. Step 1: Understand static variable behavior inside function

   The static variable 'count' retains its value between function calls and initializes only once.

2. Step 2: Trace the loop and function calls

   Each call to func() increments count: first call prints 1, second 2, third 3.

3. Final Answer:

   1 2 3 -> Option A

4. Quick Check:

   Static variable increments across calls = 1 2 3 [OK]

Hint: Static variables keep value between calls [OK]

Common Mistakes:

• Assuming static variable resets each call
• Confusing static with automatic variables
• Ignoring initialization behavior

4. Identify the error in the following C code related to storage class usage:

extern int x = 10;

int main() {
    printf("%d", x);
    return 0;
}

medium

A. Missing 'static' keyword before 'int x'

B. 'x' should be declared inside main function

C. 'extern' variable cannot be initialized

D. No error, code runs fine

Solution

1. Step 1: Understand 'extern' storage class rules

   An 'extern' variable declaration cannot have an initializer; it only declares the variable.

2. Step 2: Analyze the code

   Here, 'extern int x = 10;' tries to initialize 'x' which is invalid and causes a compilation error.

3. Final Answer:

   'extern' variable cannot be initialized -> Option C

4. Quick Check:

   Extern declarations must not initialize variables [OK]

Hint: Extern declarations cannot initialize variables [OK]

Common Mistakes:

• Initializing extern variables
• Assuming extern means static
• Declaring variables only inside main

5. You want a variable in C that keeps its value between function calls but is only accessible inside that function. Which storage class should you use?

hard

A. static

B. extern

C. auto

D. register

Solution

1. Step 1: Understand variable lifetime and scope requirements

   The variable must keep its value between calls (persistent lifetime) and be local to the function (limited scope).

2. Step 2: Match storage classes to requirements

   'static' inside a function keeps the variable value between calls and restricts scope to that function.

3. Final Answer:

   static -> Option A

4. Quick Check:

   Static inside function = persistent and local [OK]

Hint: Use static for persistent local variables [OK]

Common Mistakes:

• Using auto which resets each call
• Using extern which is global
• Using register which is for CPU registers