Scope of variables - Step-by-Step Execution

Concept Flow - Scope of variables

Start Program

↓

Declare Global Variable

↓

Enter Function

↓

Declare Local Variable

↓

Use Variables

↓

Exit Function

↓

End Program

This flow shows how variables declared globally and locally are accessed and used inside and outside functions.

Execution Sample

C

#include <stdio.h>
int x = 10; // global

void func() {
  int x = 5; // local
  printf("%d\n", x);
}

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

This code shows a global variable x and a local variable x inside func(), printing both to show scope differences.

Execution Table

Step	Action	Variable x Value	Output
1	Program starts, global x declared	10 (global)
2	Enter func(), local x declared	5 (local shadows global)
3	Print x inside func()	5 (local)	5
4	Exit func(), local x destroyed	10 (global remains)
5	Print x inside main()	10 (global)	10
6	Program ends	10 (global)

💡 Program ends after printing local and global x values showing scope difference.

Variable Tracker

Variable	Start	Inside func() start	Inside func() print	After func() end	main() print	End
x	10 (global)	5 (local shadows global)	5 (local)	10 (global)	10 (global)	10 (global)

Key Moments - 3 Insights

Why does the local variable x inside func() not change the global x?

Because the local x declared inside func() creates a new variable that only exists during func() execution, shadowing the global x. See execution_table steps 2 and 4.

What value of x is printed inside func() and why?

The value 5 is printed because inside func(), the local x (value 5) shadows the global x (value 10). See execution_table step 3.

Why does main() print the global x value 10 after func() ends?

Because the local x inside func() is destroyed after func() ends, so main() accesses the global x which remains 10. See execution_table steps 4 and 5.

Visual Quiz - 3 Questions

Look at the execution_table, what is the value of x printed inside func() at step 3?

A 5

B 10

C Undefined

D 0

💡 Hint

Check the 'Output' column at step 3 in the execution_table.

At which step does the local variable x get destroyed?

A Step 2

B Step 4

C Step 3

D Step 5

💡 Hint

Look at the 'Action' column describing variable scope changes in execution_table.

If the local variable x inside func() was not declared, what would func() print?

A 5

B 0

C 10

D Compilation error

💡 Hint

Refer to variable_tracker and understand which x is accessed if local x is missing.

Concept Snapshot

Scope of variables in C:
- Global variables declared outside functions are accessible everywhere.
- Local variables declared inside functions exist only during that function's execution.
- Local variables can shadow global variables with the same name.
- After function ends, local variables are destroyed.
- Accessing a variable uses the closest scope first.

Full Transcript

This visual trace shows how variable scope works in C. A global variable x is declared with value 10. Inside the function func(), a local variable x with value 5 is declared, which shadows the global x. When func() prints x, it shows 5. After func() ends, the local x is destroyed, and main() prints the global x value 10. This demonstrates that local variables exist only inside their function and do not affect global variables with the same name.