Pointers and arrays in C++ - Step-by-Step Execution

Concept Flow - Pointers and arrays

Declare array

→Array memory allocated

↓

Declare pointer

→Pointer assigned to array start

↓

Access elements via pointer

↓

Pointer arithmetic to move through array

↓

Read or modify array elements

↓

End

This flow shows how an array is declared and how a pointer can be assigned to its first element. Then, the pointer moves through the array to access or change elements.

Execution Sample

C++

int arr[3] = {10, 20, 30};
int* p = arr;
int first = *p;
p++;
int second = *p;

This code declares an array and a pointer to its first element, then reads the first and second elements using the pointer.

Execution Table

Step	Action	Pointer p	Value pointed by p (*p)	Variables	Output
1	Declare array arr with values {10, 20, 30}	N/A	N/A	arr = {10,20,30}	N/A
2	Declare pointer p and assign to arr (start of array)	Address of arr[0]	10	p -> arr[0]	N/A
3	Read first element via *p	Address of arr[0]	10	first = 10	first = 10
4	Increment pointer p (p++)	Address of arr[1]	20	p -> arr[1]	N/A
5	Read second element via *p	Address of arr[1]	20	second = 20	second = 20
6	End of execution	Address of arr[1]	20	first=10, second=20	Program ends

💡 Pointer p has moved through array elements; program ends after reading second element.

Variable Tracker

Variable	Start	After Step 2	After Step 3	After Step 4	After Step 5	Final
arr	{10,20,30}	{10,20,30}	{10,20,30}	{10,20,30}	{10,20,30}	{10,20,30}
p	Uninitialized	Points to arr[0]	Points to arr[0]	Points to arr[1]	Points to arr[1]	Points to arr[1]
first	Uninitialized	Uninitialized	10	10	10	10
second	Uninitialized	Uninitialized	Uninitialized	Uninitialized	20	20

Key Moments - 3 Insights

Why does incrementing the pointer (p++) move to the next array element?

Because in C++, pointer arithmetic moves the pointer by the size of the data type it points to. Here, p points to int, so p++ moves to the next int in the array (next element). See execution_table step 4.

Why can we assign the array name 'arr' directly to the pointer 'p'?

Because the array name 'arr' represents the address of its first element. So assigning p = arr makes p point to arr[0]. See execution_table step 2.

What does *p mean when p is a pointer?

*p means accessing the value stored at the memory location p points to. So *p reads or writes the array element p points to. See execution_table steps 3 and 5.

Visual Quiz - 3 Questions

Look at the execution_table at step 4. What does pointer p point to after p++?

A arr[2] (value 30)

B arr[0] (value 10)

C arr[1] (value 20)

D Null pointer

💡 Hint

Check the 'Pointer p' and '*p' columns at step 4 in execution_table.

At which step is the variable 'first' assigned a value?

A Step 2

B Step 3

C Step 4

D Step 5

💡 Hint

Look at the 'Variables' column in execution_table to see when 'first' gets a value.

If we did not increment pointer p (no p++), what would 'second' be assigned at step 5?

A 10

B 20

C Undefined

D 30

💡 Hint

Without p++ pointer stays at arr[0], so *p reads arr[0] value. See variable_tracker for pointer positions.

Concept Snapshot

Pointers and arrays in C++:
- Array name is address of first element
- Pointer can point to array start: int* p = arr;
- *p accesses value pointed by p
- p++ moves pointer to next element (by sizeof element)
- Use pointers to traverse or modify arrays efficiently

Full Transcript

This lesson shows how arrays and pointers work together in C++. We start by declaring an array of integers. The array name represents the address of its first element. We declare a pointer and assign it to the array name, so it points to the first element. Using *p, we read the value at the pointer. Incrementing the pointer with p++ moves it to the next element in the array. We then read the second element using *p again. The execution table tracks each step, showing pointer position and values accessed. Key moments clarify why pointer arithmetic works and what *p means. The quiz tests understanding of pointer movement and variable assignments. This helps beginners see how pointers and arrays connect in memory.