C Pointer Arithmetic

1. What is Pointer Arithmetic?

Pointer arithmetic allows you to move a pointer through memory based on the size of the data type it points to.
You can perform arithmetic operations like:

Increment: ptr++ → points to the next element
Decrement: ptr-- → points to the previous element
Addition: ptr + n → points to n elements ahead
Subtraction: ptr - n → points to n elements back
Difference: ptr1 - ptr2 → number of elements between two pointers

Important: Pointer arithmetic automatically accounts for the size of the data type.

2. Basic Example with int Array

#include <stdio.h>

int main() {
int numbers[5] = {10, 20, 30, 40, 50};
int *ptr = numbers; // points to numbers[0]

printf("Pointer points to: %d\n", *ptr); // 10

ptr++; // move to next element
printf("Pointer points to: %d\n", *ptr); // 20

ptr += 2; // move 2 elements ahead
printf("Pointer points to: %d\n", *ptr); // 40

ptr--; // move back 1 element
printf("Pointer points to: %d\n", *ptr); // 30

return 0;
}

#include <stdio.h>

int main() {

int numbers[5] = {10, 20, 30, 40, 50};

int *ptr = numbers; // points to numbers[0]

printf("Pointer points to: %d\n", *ptr); // 10

ptr++; // move to next element

printf("Pointer points to: %d\n", *ptr); // 20

ptr += 2; // move 2 elements ahead

printf("Pointer points to: %d\n", *ptr); // 40

ptr--; // move back 1 element

printf("Pointer points to: %d\n", *ptr); // 30

return 0;

}

Output:

Notice how pointer moves by 4 bytes each time (for int) on most systems.

3. Pointer Arithmetic with Array Indexing

Array indexing is equivalent to pointer arithmetic:

numbers + 2 → address of 3rd element
*(numbers + 2) → value at that address

4. Difference Between Two Pointers

#include <stdio.h>

int main() {
int numbers[5] = {10, 20, 30, 40, 50};
int *ptr1 = &numbers[1]; // points to 20
int *ptr2 = &numbers[4]; // points to 50

printf("Number of elements between ptr2 and ptr1: %ld\n", ptr2 - ptr1);

return 0;
}

#include <stdio.h>

int main() {

int numbers[5] = {10, 20, 30, 40, 50};

int *ptr1 = &numbers[1]; // points to 20

int *ptr2 = &numbers[4]; // points to 50

printf("Number of elements between ptr2 and ptr1: %ld\n", ptr2 - ptr1);

return 0;

}

Output:

Subtracting pointers gives the number of elements, not bytes.

5. Pointer Arithmetic with char Array (String)

#include <stdio.h>

int main() {
char str[] = "Hello";
char *ptr = str;

printf("%c\n", *ptr); // H
ptr++; // move to next character
printf("%c\n", *ptr); // e
ptr += 3; // move 3 characters ahead
printf("%c\n", *ptr); // o

return 0;
}

#include <stdio.h>

int main() {

char str[] = "Hello";

char *ptr = str;

printf("%c\n", *ptr); // H

ptr++; // move to next character

printf("%c\n", *ptr); // e

ptr += 3; // move 3 characters ahead

printf("%c\n", *ptr); // o

return 0;

}

Output:

For char, each pointer increment moves 1 byte (size of char).

6. Key Points About Pointer Arithmetic

Only valid on pointers to elements of an array or contiguous memory.
ptr++ moves to the next element (not next byte).
ptr + n moves n elements forward.
Subtracting pointers gives distance in elements, not bytes.
Works for int, char, float, double, etc., adjusting automatically for size.

C Pointer Arithmetic

1. What is Pointer Arithmetic?

2. Basic Example with int Array

3. Pointer Arithmetic with Array Indexing

4. Difference Between Two Pointers

5. Pointer Arithmetic with char Array (String)

6. Key Points About Pointer Arithmetic

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C Pointer Arithmetic

1. What is Pointer Arithmetic?

2. Basic Example with int Array

3. Pointer Arithmetic with Array Indexing

4. Difference Between Two Pointers

5. Pointer Arithmetic with char Array (String)

6. Key Points About Pointer Arithmetic

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