C Programming Pointers and Arrays

Arrays are closely related to pointers in C programming but the important difference between them is that, a pointer variable can take different addresses as value whereas, in case of array it is fixed. This can be demonstrated by an example:


#include <stdio.h>
int main(){
   char c[4];
   int i;
   for(i=0;i<4;++i){
      printf("Address of c[%d]=%x\n",i,&c[i]);
   }
   return 0;
}
Address of c[0]=28ff44
Address of c[1]=28ff45
Address of c[2]=28ff46
Address of c[3]=28ff47

Notice, that there is equal difference (difference of 1 byte) between any two consecutive elements of array.

Note: You may get different address of an array.

Relation between Arrays and Pointers

Consider and array:

int arr[4];

Relation between arrays and pointers

In arrays of C programming, name of the array always points to the first element of an array. Here, address of first element of an array is &arr[0]. Also, arr represents the address of the pointer where it is pointing. Hence, &arr[0] is equivalent to arr.

Also, value inside the address &arr[0] and address arr are equal. Value in address &arr[0] is arr[0] and value in address arr is *arr. Hence, arr[0] is equivalent to *arr.

Similarly,

&a[1] is equivalent to (a+1)  AND, a[1] is equivalent to *(a+1).
&a[2] is equivalent to (a+2)  AND, a[2] is equivalent to *(a+2).
&a[3] is equivalent to (a+1)  AND, a[3] is equivalent to *(a+3).
.
.
&a[i] is equivalent to (a+i)  AND, a[i] is equivalent to *(a+i).

In C, you can declare an array and can use pointer to alter the data of an array.

//Program to find the sum of six numbers with arrays and pointers.
#include <stdio.h>
int main(){
  int i,class[6],sum=0;
  printf("Enter 6 numbers:\n");
  for(i=0;i<6;++i){
      scanf("%d",(class+i)); // (class+i) is equivalent to &class[i]
      sum += *(class+i); // *(class+i) is equivalent to class[i]
  }
  printf("Sum=%d",sum);
  return 0;
}

Output

Enter 6 numbers:
2
3
4
5
3
4
Sum=21