Pointer and variable relationship in C++ - Step-by-Step Execution

Concept Flow - Pointer and variable relationship

Declare variable x

↓

Assign value to x

↓

Declare pointer p

↓

Assign address of x to p

↓

Access value via *p

↓

Modify x via *p

↓

End

This flow shows how a pointer stores the address of a variable and can be used to access or modify that variable.

Execution Sample

C++

int x = 10;
int* p = &x;
*p = 20;
std::cout << x;

This code creates an integer variable x, a pointer p to x, changes x through p, and prints x.

Execution Table

Step	Action	Variable x	Pointer p	Dereferenced *p	Output
1	Declare x and assign 10	10	undefined	undefined
2	Declare pointer p and assign address of x	10	address_of_x	10
3	Assign 20 to *p (changes x)	20	address_of_x	20
4	Print x	20	address_of_x	20	20

💡 Program ends after printing the updated value of x.

Variable Tracker

Variable	Start	After Step 1	After Step 2	After Step 3	Final
x	undefined	10	10	20	20
p	undefined	undefined	address_of_x	address_of_x	address_of_x

Key Moments - 3 Insights

Why does changing *p also change x?

Because p stores the address of x, *p accesses the value at that address, so modifying *p changes x directly (see Step 3 in execution_table).

What does *p mean in this code?

*p means 'the value at the address stored in p'. Since p points to x, *p is the same as x (see Step 2 and 3).

Why do we use &x when assigning to p?

&x means 'the address of x'. We assign this address to p so p points to x (see Step 2).

Visual Quiz - 3 Questions

Look at the execution_table, what is the value of x after Step 3?

A 10

B 20

C undefined

D address_of_x

💡 Hint

Check the 'Variable x' column at Step 3 in the execution_table.

At which step does pointer p get assigned the address of x?

A Step 1

B Step 3

C Step 2

D Step 4

💡 Hint

Look at the 'Action' column in execution_table for when p is assigned.

If we change *p = 30; at Step 3, what will be printed at Step 4?

A 30

B 10

C 20

D address_of_x

💡 Hint

Changing *p changes x, so check the 'Variable x' value after Step 3.

Concept Snapshot

Pointer and variable relationship in C++:
- Declare variable: int x = value;
- Declare pointer: int* p = &x; (store address of x)
- Access value via pointer: *p
- Changing *p changes x directly
- &x gives address of x
Pointers hold addresses, *p accesses the value at that address.

Full Transcript

This example shows how a pointer relates to a variable in C++. First, we declare an integer variable x and assign it the value 10. Then, we declare a pointer p and assign it the address of x using &x. The pointer p now points to x. When we assign 20 to *p, we change the value of x through the pointer. Finally, printing x shows the updated value 20. The key idea is that pointers store addresses, and dereferencing a pointer (*p) accesses or modifies the value at that address.