Pointer vs Array in C

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Arrays and Pointers are two important language constructs in C, associated with each other in many ways. In many cases, the tasks that you perform with a pointer can also be performed with the help of an array.

However, there are certain conceptual differences between arrays and pointers. Read this chapter to understand their differences and comparative advantages and disadvantages.

Arrays in C

In a C program, an array is an indexed collection of elements of similar type, stored in adjacent memory locations.

To declare an array, we use the following syntax −

data_type arr_name [size];

The size should be a non-negative integer. For example −

int arr[5];

The array can be initialized along with the declaration, with the elements given as a comma-separated list inside the curly brackets. Mentioning its size is optional.

int arr[] = {1, 2, 3, 4, 5};

Each element in an array is characterized by a unique integral index, starting from "0". In C language, the lower bound of an array is always "0" and the upper bound is "size – 1".

Pointers in C

C allows you to access the memory location of a variable that has been randomly allocated by the compiler. The address−of operator (&) returns the address of the variable.

A variable that stores the address of another variable is called a pointer. The type of the pointer must be the same as the one whose address it stores.

To differentiate from the target variable type, the name of the pointer is prefixed with an asterisk (*). If we have an int variable, its pointer is declared as "int *".

int x = 5;
int *y = &a;

Note: In case of an array, the address of its 0th element is assigned to the pointer.

int arr[] = {1, 2, 3, 4, 5};
int *ptr = &arr[0];

In fact, the name of the array itself resolves to the address of the 0th element.

Hence, we can as well write −

int *ptr = arr;

Since the elements of an array are placed in adjacent memory locations and the address of each subscript increments by 4 (in case of an int array), we can use this feature to traverse the array elements with the help of pointer as well.

Example 1: Traversing an Array with Indexed Subscripts

The following example shows how you can traverse an array with indexed subscripts −

#include <stdio.h>

int main (){

   /* an array with 5 elements */
   int arr[5] = {10, 20, 30, 40, 50};

   int i;

   /* output each array element's value */
   printf("Array values with subscripts: \n");

   for(i = 0; i < 5; i++){
      printf("arr[%d]: %d\n", i, arr[i]);
   }
   
   return 0;
}

Output

When you run this code, it will produce the following output −

Array values with subscripts:
arr[0]: 10
arr[1]: 20
arr[2]: 30
arr[3]: 40
arr[4]: 50

Example 2: Traversing an Array with Pointer

The following example shows how you can traverse an array with a pointer −

#include <stdio.h>

int main (){

   /* an array with 5 elements */
   int arr[5] = {10, 20, 30, 40, 50};
   int *x = arr;

   int i;

   /* output each array element's value */
   printf("Array values with pointer: \n");

   for(i = 0; i < 5; i++) {
      printf("arr[%d]: %d\n", i, *(x+i));
   }

   return 0;
}

Output

Run the code and check its output −

Array values with pointer
arr[0]: 10
arr[1]: 20
arr[2]: 30
arr[3]: 40
arr[4]: 50

Difference between Arrays and Pointers in C

The following table highlights the important differences between arrays and pointers −