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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): %fn", i, *(ptr + i)); } printf("nArray values using balance as address:n"); for(i = 0; i < 5; i++){ printf("*(balance + %d): %fn", 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.
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