In this tutorial, we will discuss how to access an array using a pointer.
Using a pointer variable we can hold the base address of an array. If it's a one-dimensional array, we can use a single pointer to hold its address. If the array is two-dimensional, we need to declare a pointer to the pointer to hold its base address.
In the following example, we have declared a one-dimensional array. Using a pointer variable
ptr, we are holding the address of the array. Now, the variable ptr is being used to access the array.In this example, if we perform
ptr++, the pointer points to the next element of the array as the pointer holds the address of the array.But,
arr++ means we are trying to change the base address of the array, which is not possible. You can see that the statement arr++ is commented as it is not possible.Note that the pointer variables are mutable, whereas array names are immutable.
One-dimensional Array and Pointer
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#include <stdio.h>
int main(void)
{
int arr[] = {1, 2, 5, 8, 7, 30, 15};
int *ptr;
ptr = arr; //ptr points to the base address of the array
printf("\n%u", arr); //base address of the array
printf("\n%d", arr[3]); //element of the 3rd index of the array
printf("\n%d", 3[arr]); //element of the 3rd index of the array
printf("\n%u", ptr); //base address of the array
printf("\n%u", &ptr); //address of ptr
printf("\n%d", *ptr); //element of the 0th index of the array
printf("\n%d", *(ptr + 3)); //element of the 3rd index of the array
printf("\n%u", arr); //base address of the array
printf("\n%u", &arr); //base address of the array
printf("\n%d", *arr); //element of the 0th index of the array
printf("\n%d", *(arr + 3)); //element of the 3rd index of the array
printf("\n%d", ptr[4]); //element of the 4th index of the array
printf("\n%d", 4[ptr]); //element of the 4th index of the array
ptr++; //ptr points to the address of the 1st index of the array
// arr++;
printf("\n%d", *ptr); //element of the 1st index of the array
printf("\n%d", *arr); //element of the 0th index of the array
printf("\n\n");
return 0;
}
Output
Multi-dimensional Array and Pointer
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#include <stdio.h>
int main(void)
{
int arr[10][10], i, j;
for(i = 0; i < 10; i++)
for(j = 0; j < 10; j++)
scanf("%d", (*(arr + i) + j));
// print the element of position (2, 7)
printf(" %d ", *(*(arr + 2) + 7));
return 0;
Array of Pointers
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#include <stdio.h>
#include <stdlib.h>
int main(void)
{
int *arr[10], n, i, j;
printf("Enter number of columns (>= 8):");
scanf("%d", &n);
for(i = 0; i < n; i++)
arr[i] = (int *) calloc(n, sizeof(int));
for(i = 0; i < 10; i++)
for(j = 0; j < n; j++)
scanf("%d", (*(arr + i) + j));
// print an element from position (2, 7)
printf(" %d ", *(*(arr + 2) + 7));
return 0;
}
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