QUESTION 11 · Pointers and Arrays

What does an array expression usually become in an expression?

2 marks

Answer

It usually converts to a pointer to its first element.

For int a[3], int *p = a; makes p identify a[0].
The array object and the pointer variable are still different kinds of objects.

Explain the relationship between pointers and one-dimensional arrays.

5 marks

Answer in brief

An array contains its elements, while a pointer can identify an element. Their close relationship makes pointer-based traversal possible, but they are not identical types.

Example

int a[3] = {4, 5, 6};
int *p = a;

Indexed and indirect access

For a valid index i, a[i] means *(a + i). With p pointing at the first element, p[i] and *(p + i) also access that element. The sample visits all three values through p and prints 4, 5 and 6.

Important differences

The array declaration reserves storage for all three ints; declaring p reserves only a pointer object.
p can be assigned another compatible address. The array name is not a modifiable pointer variable that can be incremented.
sizeof a gives the whole array size where the actual declaration is visible, while sizeof p gives the pointer size.
&a has a pointer-to-array type, which differs from the pointer-to-element type produced by a in most expressions.

Function connection

A parameter written int a[] adjusts to int *a. That parameter does not retain the caller’s complete array length. Pass a suitable count separately and keep every access within the actual array.

Complexity

A direct valid access takes O(1) time in the usual model. Traversing n elements through a pointer still takes O(n): pointer notation does not remove the need to visit every element. This traversal uses O(1) auxiliary space beyond the array.

Comparison table

↔ Scroll horizontally on a small screen

Array and pointer objects
Feature	int a[3]	int *p
Stored object	Three contiguous int elements	One pointer value
Reassignment	Array not assignable as a whole	Pointer can be reassigned
sizeof on actual declaration	Entire array size	Pointer size
Length knowledge	Known from actual array type	Not carried by pointer alone

C program and output

Download .c Open compiler

/* CodeBhavya | PPS AR25 | Learning example */
#include <stdio.h>

int main(void)
{
    int a[3] = {4, 5, 6};
    int *p = a;
    for (int i = 0; i < 3; ++i) { printf("%d\n", *(p + i)); }
    return 0;
}

Sample input and output

This example uses values already written in the program.

Output

4
5
6