Scope of variables - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the scope of a variable in C?

The scope of a variable in C is the part of the program where the variable can be accessed or used.

beginner

What is the difference between local and global variables?

Local variables are declared inside a function and can only be used within that function. Global variables are declared outside all functions and can be used anywhere in the program after their declaration.

intermediate

What happens if a local variable and a global variable have the same name?

The local variable will hide or override the global variable inside its scope (usually inside the function). Outside the function, the global variable is used.

beginner

What is block scope in C?

Block scope means a variable declared inside a pair of braces { } is only accessible inside those braces.

intermediate

What is the scope of a static variable inside a function?

A static variable inside a function keeps its value between calls but is only accessible inside that function.

Where can a global variable be accessed in a C program?

A Only inside the block where it is declared

B Only inside the function where it is declared

C Anywhere in the program after its declaration

D Nowhere, global variables do not exist in C

Global variables are declared outside all functions and can be accessed anywhere after their declaration.

What is the scope of a variable declared inside a for loop in C?

A Only inside the for loop block

B Entire program

C Only inside the function containing the loop

D Global scope

Variables declared inside the for loop block have block scope and are accessible only inside that block.

If a local variable and a global variable share the same name, which one is used inside the function?

A Local variable

B Global variable

C Both variables are used simultaneously

D Compilation error

The local variable hides the global variable inside the function scope.

What does the static keyword do when used with a variable inside a function?

A Makes the variable global

B Makes the variable accessible only outside the function

C Deletes the variable after the function ends

D Keeps the variable value between function calls and limits scope to the function

Static variables inside functions retain their value between calls and are only accessible inside that function.

Which of these is NOT a valid scope type in C?

A Local scope

B Class scope

C Block scope

D Global scope

C does not have class scope because it is not an object-oriented language.

Explain the difference between local and global variables in C and give an example of each.

Think about where the variables are declared and where they can be used.

Describe what happens when a local variable has the same name as a global variable in C.

Consider which variable the program uses inside the function.

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