Pointer to an Array in C

---

---

An array name is a constant pointer to the first element of the array. Therefore, in this declaration,

 int balance[5]; 

balance is a pointer to &balance[0], which is the address of the first element of the array.

Example

In this code, we have a pointer ptr that points to the address of the first element of an integer array called balance.

 #include <stdio.h> int main(){ int *ptr; int balance[5] = {1, 2, 3, 4, 5}; ptr = balance; printf("Pointer 'ptr' points to the address: %d", ptr); printf("\nAddress of the first element: %d", balance); printf("\nAddress of the first element: %d", &balance[0]); return 0; } 

Output

In all the three cases, you get the same output −

 Pointer 'ptr' points to the address: 647772240 Address of the first element: 647772240 Address of the first element: 647772240 

If you fetch the value stored at the address that ptr points to, that is *ptr, then it will return 1.

Array Names as Constant Pointers

It is legal to use array names as constant pointers and vice versa. Therefore, *(balance + 4) is a legitimate way of accessing the data at balance[4].

Once you store the address of the first element in "ptr", you can access the array elements using *ptr, *(ptr + 1), *(ptr + 2), and so on.

Example

The following example demonstrates all the concepts discussed above −

 #include <stdio.h> int main(){ /* an array with 5 elements */ double balance[5] = {1000.0, 2.0, 3.4, 17.0, 50.0}; double *ptr; int i; ptr = balance; /* output each array element's value */ printf("Array values using pointer: \n"); for(i = 0; i < 5; i++){ printf("*(ptr + %d): %f\n", i, *(ptr + i)); } printf("\nArray values using balance as address:\n"); for(i = 0; i < 5; i++){ printf("*(balance + %d): %f\n", i, *(balance + i)); } return 0; } 

Output

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

 Array values using pointer: *(ptr + 0): 1000.000000 *(ptr + 1): 2.000000 *(ptr + 2): 3.400000 *(ptr + 3): 17.000000 *(ptr + 4): 50.000000 Array values using balance as address: *(balance + 0): 1000.000000 *(balance + 1): 2.000000 *(balance + 2): 3.400000 *(balance + 3): 17.000000 *(balance + 4): 50.000000 

In the above example, ptr is a pointer that can store the address of a variable of double type. Once we have the address in ptr, *ptr will give us the value available at the address stored in ptr.