Scope of variables - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to declare a global variable.

C

#include <stdio.h>

[1] count = 10;

int main() {
    printf("Count is %d\n", count);
    return 0;
}

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

Aextern

Bint

Cstatic

Dregister

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'static' limits the variable to the file scope but is not necessary here.

Using 'extern' without defining the variable causes linker errors.

Using 'register' is only for local variables and hints to store in CPU registers.

The keyword int declares the variable count as a global integer variable accessible throughout the file.

2fill in blank

medium

Complete the code to declare a local variable inside main.

C

#include <stdio.h>

int main() {
    [1] number = 5;
    printf("Number is %d\n", number);
    return 0;
}

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

Aint

Bstatic

Cextern

Dregister

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'extern' inside a function is incorrect for local variables.

Using 'static' inside a function changes the variable lifetime but is not required here.

Using 'register' is optional and hints to store in CPU registers.

The keyword int declares a local integer variable number inside the main function.

3fill in blank

hard

Fix the error in the code by choosing the correct keyword for the variable inside the function.

C

#include <stdio.h>

int count = 20;

int main() {
    [1] count = 10;
    printf("Count is %d\n", count);
    return 0;
}

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

Aint

Bstatic

Cextern

Dregister

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'extern' inside a function without definition causes errors.

Using 'static' changes lifetime but is not necessary here.

Using 'register' is optional and unrelated to the error.

Declaring int count = 10; inside main creates a local variable that hides the global count. This is valid and fixes the error.

4fill in blank

hard

Fill both blanks to declare a static variable inside a function and initialize it.

C

#include <stdio.h>

void func() {
    [1] int counter = [2];
    counter++;
    printf("Counter: %d\n", counter);
}

int main() {
    func();
    func();
    return 0;
}

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

Astatic

B10

C0

Dextern

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'extern' inside a function is invalid.

Initializing static variables to 10 will start counting from 10, not zero.

Not using 'static' will reset the variable each call.

Using static makes counter keep its value between calls. Initializing it to 0 starts counting from zero.

5fill in blank

hard

Fill all three blanks to create a function that modifies a global variable.

C

#include <stdio.h>

[1] total = 0;

void add(int value) {
    total [2]= value;
}

int main() {
    add([3]);
    printf("Total: %d\n", total);
    return 0;
}

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

Astatic

B+

C5

Dint

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'static' for global variable limits its scope to the file.

Using '-' instead of '+' will subtract instead of add.

Calling add with no argument or wrong value causes errors.

Declare total as a global int. Use += to add value to total. Call add(5) to add 5 to total.

Practice

1. What is the scope of a variable declared inside a function in C?

easy

A. It can be accessed only in the main function.

B. It is global and can be accessed anywhere in the program.

C. It is local to that function and cannot be accessed outside.

D. It is accessible only in loops inside the function.

Solution

1. Step 1: Understand variable declaration inside a function

   A variable declared inside a function is created when the function starts and destroyed when it ends.

2. Step 2: Identify the scope of such variables

   These variables are local to the function and cannot be accessed outside it.

3. Final Answer:

   It is local to that function and cannot be accessed outside. -> Option C

4. Quick Check:

   Local variable scope = inside function only [OK]

Hint: Local variables stay inside their function only [OK]

Common Mistakes:

• Thinking local variables are global
• Assuming local variables exist outside function
• Confusing local with static variables

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

easy

A. int x; // declared outside any function

B. int x; inside main()

C. static int x; inside a function

D. int x; inside a loop

Solution

1. Step 1: Identify global variable declaration

   Global variables are declared outside all functions, usually at the top of the file.

2. Step 2: Check each option

   int x; // declared outside any function declares int x; outside any function, which is correct for global scope.

3. Final Answer:

   int x; // declared outside any function -> Option A

4. Quick Check:

   Global variables declared outside functions [OK]

Hint: Globals declared outside all functions [OK]

Common Mistakes:

• Declaring globals inside functions
• Using static inside functions for globals
• Declaring variables inside loops thinking they are global

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

int x = 5;
void func() {
    int x = 10;
    printf("%d", x);
}
int main() {
    func();
    printf(" %d", x);
    return 0;
}

medium

A. 10 10

B. 5 10

C. 5 5

D. 10 5

Solution

1. Step 1: Analyze variable scopes in func()

   Inside func(), a local variable x is declared with value 10, which hides the global x.

2. Step 2: Check printf outputs

   First printf prints local x (10). Then main prints global x (5).

3. Final Answer:

   10 5 -> Option D

4. Quick Check:

   Local hides global inside function [OK]

Hint: Local variable hides global inside function [OK]

Common Mistakes:

• Assuming global x prints inside func()
• Mixing order of printed values
• Ignoring local variable shadowing

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

void func() {
    printf("%d", x);
}
int main() {
    int x = 5;
    func();
    return 0;
}

medium

A. x is not declared globally, so func() cannot access it

B. Variable x is used before declaration in func()

C. Missing return type for main()

D. Syntax error in printf statement

Solution

1. Step 1: Check variable x usage in func()

   func() tries to print x but x is declared only inside main(), so func() cannot see it.

2. Step 2: Understand variable scope rules

   Variables declared inside main() are local to main() only, not visible in other functions.

3. Final Answer:

   x is not declared globally, so func() cannot access it -> Option A

4. Quick Check:

   Local variables not visible outside their function [OK]

Hint: Functions can't access locals from other functions [OK]

Common Mistakes:

• Thinking main()'s x is global
• Ignoring variable scope rules
• Assuming implicit global variables

5. Consider the following C code:

int x = 1;
void outer() {
    int x = 2;
    {
        int x = 3;
        printf("%d ", x);
    }
    printf("%d ", x);
}
int main() {
    outer();
    printf("%d", x);
    return 0;
}

What is the output when this program runs?

hard

A. 1 2 3

B. 3 2 1

C. 3 3 3

D. 2 3 1

Solution

1. Step 1: Analyze innermost block variable

   The innermost block declares x = 3, so first printf prints 3.

2. Step 2: Analyze outer block variable

   After inner block ends, the x = 3 goes out of scope, so next printf prints outer x = 2.

3. Step 3: Analyze global variable in main()

   Finally, main prints global x = 1.

4. Final Answer:

   3 2 1 -> Option B

5. Quick Check:

   Inner blocks hide outer variables [OK]

Hint: Inner block variables override outer ones [OK]

Common Mistakes:

• Ignoring block-level scope
• Assuming all x print same value
• Confusing order of prints