Pointers & Arrays

Relationship Between Pointers & Arrays

In C, the name of an array represents the base address of the array.

• a → base address of array
• &a[0] → address of first element
• *(a) → value of first element
• *(a + i) → value of ith element
• a[i] is same as *(a + i)

Pointer to an Array Element

A pointer can point to any element inside an array:

int arr[5] = {10, 20, 30, 40, 50};
int *p = &arr[0];

Pointer Arithmetic

• p + 1 → moves to next element
• p - 1 → moves back one element
• Pointer increments by the size of its data type
• Works only inside same array range

Advantages of Using Pointers with Arrays

• Efficient element access
• Fast traversal
• Used in dynamic arrays (malloc)
• Required in strings & matrices
• Used in function parameter passing

10 Examples of Pointers & Arrays

Example 1 – Basic Pointer to Array

#include <stdio.h>

int main(){
    int a[3] = {10, 20, 30};
    int *p = a;

    printf("%d", *p);   // 10
    return 0;
}

Example 2 – Access Using Pointer Arithmetic

#include <stdio.h>

int main(){
    int a[3] = {5, 7, 9};
    int *p = a;

    printf("%d", *(p + 1));  // 7
    return 0;
}

Example 3 – Print Full Array Using Pointer

#include <stdio.h>

int main(){
    int a[5] = {1,2,3,4,5};
    int *p = a;

    for(int i = 0; i < 5; i++)
        printf("%d ", *(p + i));

    return 0;
}

Example 4 – Modify Array Using Pointer

#include <stdio.h>

int main(){
    int a[3] = {10, 20, 30};
    int *p = a;

    *p = 99;
    printf("%d", a[0]);   // 99
    return 0;
}

Example 5 – Pointer to Specific Element

#include <stdio.h>

int main(){
    int a[4] = {2,4,6,8};
    int *p = &a[2];

    printf("%d", *p);  // 6
    return 0;
}

Example 6 – Using Array Index With Pointer

#include <stdio.h>

int main(){
    int a[4] = {3,6,9,12};
    int *p = a;

    printf("%d", p[2]); // 9
    return 0;
}

Example 7 – Pointer Traversing Backward

#include <stdio.h>

int main(){
    int a[4] = {10,20,30,40};
    int *p = &a[3];

    printf("%d", *(p - 2)); // 20
    return 0;
}

Example 8 – Sum of Elements Using Pointer

#include <stdio.h>

int main(){
    int a[5] = {1,2,3,4,5};
    int *p = a;
    int sum = 0;

    for(int i=0; i<5; i++)
        sum += *(p + i);

    printf("Sum = %d", sum);
    return 0;
}

Example 9 – Pointer to Array vs Array of Pointers

#include <stdio.h>

int main(){
    int a[3] = {10,20,30};
    int *p = a;    // pointer to array

    printf("%d", *p);
    return 0;
}

Example 10 – Passing Array to Function Using Pointer

#include <stdio.h>

void show(int *p){
    for(int i=0; i<4; i++)
        printf("%d ", p[i]);
}

int main(){
    int a[4] = {7,14,21,28};
    show(a);  // array decays to pointer
    return 0;
}

Practice Questions

1. Explain how array name works as a pointer.
2. What is pointer arithmetic? Give examples.
3. How can we modify array elements using pointers?
4. Difference between a[i] and *(a + i).
5. Write a program to find largest element using pointers.