# Pointer Arithmetics in C with Examples

• Difficulty Level : Medium
• Last Updated : 04 Jun, 2022

Pointers variables are also known as address data types because they are used to store the address of another variable. The address is the memory location that is assigned to the variable. It doesn’t store any value.

Hence, there are only a few operations that are allowed to perform on Pointers in C language. The operations are slightly different from the ones that we generally use for mathematical calculations. The operations are:

1. Increment/Decrement of a Pointer
2. Addition of integer to a pointer
3. Subtraction of integer to a pointer
4. Subtracting two pointers of the same type
5. Comparison of pointers of the same type.

Increment/Decrement of a Pointer

Increment: It is a condition that also comes under addition. When a pointer is incremented, it actually increments by the number equal to the size of the data type for which it is a pointer.

For Example:
If an integer pointer that stores address 1000 is incremented, then it will increment by 2(size of an int) and the new address it will points to 1002. While if a float type pointer is incremented then it will increment by 4(size of a float) and the new address will be 1004.
Decrement: It is a condition that also comes under subtraction. When a pointer is decremented, it actually decrements by the number equal to the size of the data type for which it is a pointer.

For Example:
If an integer pointer that stores address 1000 is decremented, then it will decrement by 2(size of an int) and the new address it will points to 998. While if a float type pointer is decremented then it will decrement by 4(size of a float) and the new address will be 996.

Below is the program to illustrate pointer increment/decrement:

## C

 `// C program to illustrate``// pointer increment/decrement` `#include ` `// Driver Code``int` `main()``{``    ``// Integer variable``    ``int` `N = 4;` `    ``// Pointer to an integer``    ``int` `*ptr1, *ptr2;` `    ``// Pointer stores``    ``// the address of N``    ``ptr1 = &N;``    ``ptr2 = &N;` `    ``printf``(``"Pointer ptr1 "``           ``"before Increment: "``);``    ``printf``(``"%p \n"``, ptr1);` `    ``// Incrementing pointer ptr1;``    ``ptr1++;` `    ``printf``(``"Pointer ptr1 after"``           ``" Increment: "``);``    ``printf``(``"%p \n\n"``, ptr1);` `    ``printf``(``"Pointer ptr1 before"``           ``" Decrement: "``);``    ``printf``(``"%p \n"``, ptr1);` `    ``// Decrementing pointer ptr1;``    ``ptr1--;` `    ``printf``(``"Pointer ptr1 after"``           ``" Decrement: "``);``    ``printf``(``"%p \n\n"``, ptr1);` `    ``return` `0;``}`

Output

```Pointer ptr1 before Increment: 0x7ffefa9c5704
Pointer ptr1 after Increment: 0x7ffefa9c5708

Pointer ptr1 before Decrement: 0x7ffefa9c5708
Pointer ptr1 after Decrement: 0x7ffefa9c5704

```

When a pointer is added with a value, the value is first multiplied by the size of data type and then added to the pointer.

## C

 `// C program to illustrate pointer Addition``#include ` `// Driver Code``int` `main()``{``    ``// Integer variable``    ``int` `N = 4;` `    ``// Pointer to an integer``    ``int` `*ptr1, *ptr2;` `    ``// Pointer stores the address of N``    ``ptr1 = &N;``    ``ptr2 = &N;` `    ``printf``(``"Pointer ptr2 before Addition: "``);``    ``printf``(``"%p \n"``, ptr2);` `    ``// Addition of 3 to ptr2``    ``ptr2 = ptr2 + 3;``    ``printf``(``"Pointer ptr2 after Addition: "``);``    ``printf``(``"%p \n"``, ptr2);` `    ``return` `0;``}`

Output

```Pointer ptr2 before Addition: 0x7fffc22348a4
```

Subtraction

When a pointer is subtracted with a value, the value is first multiplied by the size of the data type and then subtracted from the pointer.

Below is the program to illustrate pointer Subtraction:

## C

 `// C program to illustrate pointer Subtraction``#include ` `// Driver Code``int` `main()``{``    ``// Integer variable``    ``int` `N = 4;` `    ``// Pointer to an integer``    ``int` `*ptr1, *ptr2;` `    ``// Pointer stores the address of N``    ``ptr1 = &N;``    ``ptr2 = &N;` `    ``printf``(``"Pointer ptr2 before Subtraction: "``);``    ``printf``(``"%p \n"``, ptr2);` `    ``// Subtraction of 3 to ptr2``    ``ptr2 = ptr2 - 3;``    ``printf``(``"Pointer ptr2 after Subtraction: "``);``    ``printf``(``"%p \n"``, ptr2);` `    ``return` `0;``}`

Output

```Pointer ptr2 before Subtraction: 0x7ffcbed44ee4
Pointer ptr2 after Subtraction: 0x7ffcbed44ed8
```

Subtraction of Two Pointers

The subtraction of two pointers is possible only when they have the same data type. The result is generated by calculating the difference between the addresses of the two pointers and calculating how many bits of data it is according to the pointer data type. The subtraction of two pointers gives the increments between the two pointers.

For Example:
Two integer pointers say ptr1(address:1000) and ptr2(address:1016) are subtracted. The difference between address is 16 bytes. Since the size of int is 2 bytes, therefore the increment between ptr1 and ptr2 is given by (16/2) = 8.

Below is the implementation to illustrate the Subtraction of Two Pointers:

## C

 `// C program to illustrate Subtraction``// of two pointers``#include ` `// Driver Code``int` `main()``{``    ``int` `x;` `    ``// Integer variable``    ``int` `N = 4;` `    ``// Pointer to an integer``    ``int` `*ptr1, *ptr2;` `    ``// Pointer stores the address of N``    ``ptr1 = &N;``    ``ptr2 = &N;` `    ``// Incrementing ptr2 by 3``    ``ptr2 = ptr2 + 3;` `    ``// Subtraction of ptr2 and ptr1``    ``x = ptr2 - ptr1;` `    ``// Print x to get the Increment``    ``// between ptr1 and ptr2``    ``printf``(``"Subtraction of ptr1 "``           ``"& ptr2 is %d\n"``,``           ``x);` `    ``return` `0;``}`

Output

```Subtraction of ptr1 & ptr2 is 3
```

Pointer Arithmetic on Arrays:
Pointers contain addresses. Adding two addresses makes no sense because there is no idea what it would point to. Subtracting two addresses lets you compute the offset between the two addresses. An array name acts like a pointer constant. The value of this pointer constant is the address of the first element. For Example: if an array named arr then arr and &arr can be used to reference array as a pointer.

Below is the program to illustrate the Pointer Arithmetic on arrays:

Program 1:

## C

 `// C program to illustrate the array``// traversal using pointers``#include ` `// Driver Code``int` `main()``{` `    ``int` `N = 5;` `    ``// An array``    ``int` `arr[] = { 1, 2, 3, 4, 5 };` `    ``// Declare pointer variable``    ``int``* ptr;` `    ``// Point the pointer to first``    ``// element in array arr[]``    ``ptr = arr;` `    ``// Traverse array using ptr``    ``for` `(``int` `i = 0; i < N; i++) {` `        ``// Print element at which``        ``// ptr points``        ``printf``(``"%d "``, ptr);``        ``ptr++;``    ``}``}`

Output

`1 2 3 4 5 `

Program 2:

## C

 `// C program to illustrate the array``// traversal using pointers in 2D array``#include ` `// Function to traverse 2D array``// using pointers``void` `traverseArr(``int``* arr,``                 ``int` `N, ``int` `M)``{` `    ``int` `i, j;` `    ``// Traverse rows of 2D matrix``    ``for` `(i = 0; i < N; i++) {` `        ``// Traverse columns of 2D matrix``        ``for` `(j = 0; j < M; j++) {` `            ``// Print the element``            ``printf``(``"%d "``, *((arr + i * M) + j));``        ``}``        ``printf``(``"\n"``);``    ``}``}` `// Driver Code``int` `main()``{` `    ``int` `N = 3, M = 2;` `    ``// A 2D array``    ``int` `arr[] = { { 1, 2 },``                     ``{ 3, 4 },``                     ``{ 5, 6 } };` `    ``// Function Call``    ``traverseArr((``int``*)arr, N, M);``    ``return` `0;``}`

Output

```1 2
3 4
5 6
```

Comparison of pointers of the same type:

We can compare the two pointers by using the comparison operators in C. We can implement this by using all operators in C >, >=, <, <=, ==, !=.  It returns true for the valid condition and returns false for the unsatisfied condition.

Step 1 : Initialize the integer values and point these integer values to the pointer.

Step 2 : Now, check the condition by using comparison or relational operators on pointer variables.

Step 3 : Display the output.

## C

 `#include ` `int` `main() {` `    ``// code``    ``int` `num1=5,num2=6,num3=5; ``//integer input``    ``int` `*p1=&num1;``// addressing the integer input to pointer``    ``int` `*p2=&num2;``    ``int` `*p3=&num3;``    ``//comparing the pointer variables.``   ``if``(*p1<*p2)``   ``{``       ``printf``(``"\n%d less than %d"``,*p1,*p2);``   ``}``   ``if``(*p2>*p1)``   ``{``     ``printf``(``"\n%d greater than %d"``,*p2,*p1);``   ``}``   ``if``(*p3==*p1)``   ``{``      ``printf``(``"\nBoth the values are equal"``);``   ``}``   ``if``(*p3!=*p2)``   ``{``      ``printf``(``"\nBoth the values are not equal"``);``   ``}``  `  `    ``return` `0;``}`

Output

```5 less than 6
6 greater than 5
Both the values are equal
Both the values are not equal```

Comparison operators on Pointers using array :

In the below approach, it results the count of odd numbers and even numbers in an array. We are going to implement this by using pointer.

Step 1 :First, declare the length of an array and array elements.

Step 2 :Declare the pointer variable and point it to the first element of an array.

Step 3:Initialize the count_even and count_odd. Iterate the for loop and check the conditions for number of odd elements and even elements in an array,

Step 4: Increment the pointer location ptr++ to the next element in an array for further iteration.

Step 5 : Print the result.

## C

 `#include ` `int` `main()``{``    ``int` `n = 10; ``// length of an array` `    ``int` `arr[] = { 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 };``    ``int``* ptr; ``// Declaration of pointer variable` `    ``ptr = arr; ``// Pointer points the first (0th index)``               ``// element in an array``    ``int` `count_even = 0;``    ``int` `count_odd = 0;` `    ``for` `(``int` `i = 0; i < n; i++) {` `        ``if` `(*ptr % 2 == 0) {``            ``count_even++;``        ``}``        ``if` `(*ptr % 2 != 0) {``            ``count_odd++;``        ``}``        ``ptr++; ``// Pointing to the next element in an array``    ``}``    ``printf``(``"\n No of even elements in an array is : %d"``,``           ``count_even);``    ``printf``(``"\n No of odd elements in an array is : %d"``,``           ``count_odd);``}`

Output

``` No of even elements in an array is : 5
No of odd elements in an array is : 5```

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