Static storage class - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to declare a static variable inside a function.

C

void func() {
    static int [1] = 0;
    [1]++;
    printf("%d\n", [1]);
}

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

Anum

Bcount

Cvalue

Dtemp

Attempts:

3 left

💡 Hint

Common Mistakes

Using a non-static variable which resets every function call.

Forgetting to use the same variable name in all places.

The variable count is declared as static inside the function, so it keeps its value between calls.

2fill in blank

medium

Complete the code to declare a static global variable.

C

[1] int counter = 0;

void increment() {
    counter++;
}

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

Aregister

Bextern

Cauto

Dstatic

Attempts:

3 left

💡 Hint

Common Mistakes

Using extern which declares an external variable.

Using auto or register which are for local variables.

Using static before a global variable limits its scope to the current file.

3fill in blank

hard

Fix the error in the code by completing the declaration of a static variable inside a function.

C

void demo() {
    [1] int x = 5;
    x++;
    printf("%d\n", x);
}

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

Aauto

Bregister

Cstatic

Dextern

Attempts:

3 left

💡 Hint

Common Mistakes

Using auto or register which are for automatic variables.

Using extern which is for external linkage.

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

4fill in blank

hard

Fill both blanks to create a static variable inside a function and print its value.

C

void count_calls() {
    [1] int calls = 0;
    calls[2];
    printf("Calls: %d\n", calls);
}

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

Astatic

B++

C--

D+

Attempts:

3 left

💡 Hint

Common Mistakes

Using a non-static variable which resets every call.

Using the wrong operator to change the variable.

The variable calls is static and incremented each time the function runs.

5fill in blank

hard

Fill all three blanks to declare a static variable, increment it, and print its value.

C

void func() {
    [1] int num = 0;
    num[2];
    printf("Number: %d\n", [3]);
}

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

Astatic

B++

Cnum

D--

Attempts:

3 left

💡 Hint

Common Mistakes

Forgetting to declare the variable as static.

Using the wrong variable name in the print statement.

The static variable num is incremented and printed each time func is called.

Practice

1. What does the static keyword do when used with a variable inside a function in C?

easy

A. Keeps the variable value between function calls

B. Makes the variable global

C. Deletes the variable after the function ends

D. Allows the variable to be accessed from other files

Solution

1. Step 1: Understand static inside a function

   A static variable inside a function keeps its value even after the function finishes.

2. Step 2: Compare with other options

   Static does not make variables global or accessible outside the file; it preserves value only inside the function.

3. Final Answer:

   Keeps the variable value between function calls -> Option A

4. Quick Check:

   Static inside function = value preserved [OK]

Hint: Static inside function means value stays between calls [OK]

Common Mistakes:

• Thinking static makes variable global
• Assuming static deletes variable after function ends
• Confusing static with extern keyword

2. Which of the following is the correct way to declare a static variable inside a function in C?

easy

A. static count int = 0;

B. static int count = 0;

C. int static count = 0;

D. count static int = 0;

Solution

1. Step 1: Recall correct static syntax

   The correct syntax places static before the type: static int count = 0;.

2. Step 2: Check other options

   Other options have wrong order of keywords, which is invalid in C.

3. Final Answer:

   static int count = 0; -> Option B

4. Quick Check:

   Static keyword comes before type [OK]

Hint: Static always comes before the type in declaration [OK]

Common Mistakes:

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

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

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

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

medium

A. 1 1 1

B. 0 1 2

C. 1 2 3

D. 3 3 3

Solution

1. Step 1: Understand static variable behavior in func()

   The static variable x is initialized once to 0 and keeps its value between calls.

2. Step 2: Trace the loop calls

   Each call increments x by 1 and prints it. So outputs are 1, then 2, then 3.

3. Final Answer:

   1 2 3 -> Option C

4. Quick Check:

   Static variable increments across calls [OK]

Hint: Static variable keeps incrementing each call [OK]

Common Mistakes:

• Assuming static resets each call
• Confusing initial value with printed value
• Expecting output to be zeros

4. Identify the error in the following code snippet:

void func() {
    static int x;
}

int main() {
    x = 5;
    func();
    return 0;
}

medium

A. No error, code runs fine

B. Missing initialization of static variable x

C. Static variables cannot be declared inside functions

D. Static variable x cannot be assigned outside its function

Solution

1. Step 1: Check variable scope

   The static variable x is declared inside func(), so it is local to that function.

2. Step 2: Analyze assignment in main()

   Trying to assign x = 5; in main() causes an error because x is not visible outside func().

3. Final Answer:

   Static variable x cannot be assigned outside its function -> Option D

4. Quick Check:

   Static inside function = local scope [OK]

Hint: Static inside function is local, can't access outside [OK]

Common Mistakes:

• Thinking static variables are global
• Ignoring variable scope rules
• Assuming static variables must be initialized

5. Consider two C files: file1.c and file2.c.

In file1.c:

static int count = 0;

void increment() {
    count++;
}

int getCount() {
    return count;
}

In file2.c:

extern int count;

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

What will happen when you compile and run these files together?

hard

A. Compilation error due to undefined reference to count

B. Prints 1

C. Prints 0

D. Runtime error due to static variable

Solution

1. Step 1: Understand static at file scope

   The static int count has internal linkage, visible only in file1.c.

2. Step 2: Function access

   increment() and getCount() are external functions that can access the static count since they are in the same file.

3. Step 3: Analyze extern usage

   The declaration extern int count; in file2.c expects a global variable count defined elsewhere, but since count is static in file1.c, it is not visible externally, causing a linker error.

4. Final Answer:

   Compilation error due to undefined reference to count -> Option A

5. Quick Check:

   Static variables have internal linkage, extern cannot access them [OK]

Hint: Static variables limited to file scope, extern can't access [OK]

Common Mistakes:

• Assuming static variables are global across files
• Expecting extern to find static variables
• Ignoring linker errors