C Variable Scope

C Tutorial

🔐 C Variable Scope

Variable scope in C language defines where a variable can be accessed or used in a program.
Understanding scope is critical for debugging, memory management, and interviews.

1️⃣ What is Variable Scope?

Variable scope determines the visibility and lifetime of a variable.

In C, scope is mainly divided into:

  1. Local scope

  2. Global scope

  3. Block scope

  4. Function parameter scope

  5. Static scope (special case)

2️⃣ Local Variable Scope

🔹 Definition

  • Declared inside a function

  • Accessible only within that function

  • Destroyed after function execution

Example


 

✔ x is visible only inside show()

3️⃣ Global Variable Scope

🔹 Definition

  • Declared outside all functions

  • Accessible by all functions

  • Lifetime = entire program execution

Example


 

⚠️ Overuse of globals is not recommended

4️⃣ Block Scope {}

🔹 Definition

Variables declared inside { } are accessible only within that block.

Example


 

✔ y exists only inside if block

5️⃣ Function Parameter Scope

🔹 Definition

  • Function parameters act as local variables

  • Accessible only inside the function

Example


 

✔ a exists only inside print()

6️⃣ Static Variable Scope ⭐ (Very Important)

🔹 Definition

  • Declared using static

  • Scope is local, but lifetime is entire program

Example


 

✔ Output:

1
2
3

📌 Value is retained between function calls

7️⃣ Scope vs Lifetime (Interview Favorite ⭐)

Term Meaning
Scope Where variable is accessible
Lifetime How long variable exists

Example

static int x; // global scope, full lifetime

8️⃣ Variable Shadowing ⚠️

🔹 Definition

When a local variable hides a global variable with the same name.

Example


 

✔ Output: 50
✔ Global x still exists but is hidden

9️⃣ Storage Class & Scope Relation

Storage Class Scope Lifetime
auto Local Function
register Local Function
static Local / Global Program
extern Global Program

🔟 Common Mistakes ❌

❌ Using local variable outside function
❌ Confusing scope with lifetime
❌ Overusing global variables
❌ Shadowing variables unintentionally

📌 Interview Questions (Must Prepare)

  1. What is variable scope?

  2. Difference between local and global variables

  3. What is block scope?

  4. Static variable scope and lifetime

  5. What is variable shadowing?

  6. Scope vs lifetime difference

🔥 Real-Life Importance

  • Prevents bugs

  • Improves code readability

  • Essential for multi-file projects

  • Important for embedded & system programming

✅ Summary

✔ Scope defines where variable can be used
✔ Lifetime defines how long it exists
✔ Local variables are safer than globals
✔ static variables retain value
✔ Very important for interviews & real projects

You may also like...