C Pointer & Array
In C programming, a pointer is a variable that stores the memory address of another variable. It is used to get the memory address of a variable as well as the value at the memory location.
In C programming, an array is a collection of elements of the same data type stored in contiguous memory locations.
A pointer can be used to point to the elements of an array.
Various operations on arrays can be performed using pointers.
Accessing Array Elements Using a Pointer
A pointer can be used to traverse the array or access its elements.
The name of the array itself acts as a pointer to the first element of the array.
The following example demonstrates how to access array elements using a pointer:
Example of accessing array elements using a pointer
xxxxxxxxxx#include <stdio.h>int main() { int arr[] = {55, 12, 15, 25, 30}; int *ptr = arr; // Pointer pointing to the first element of the array printf("The first element of the array: %d\n", *ptr); ptr++; //Pointer 'ptr' is incremented printf("The second element of the array: %d\n", *ptr); //Printing the second element ptr += 2; //Pointer 'ptr' is incremented by 2 printf("The fourth element of the array: %d", *ptr); //Printing the fourth element return 0;}Output of the above example
The first element of the array: 55 The second element of the array: 12 The fourth element of the array: 25
Explanation of code:
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int arr[] = {55, 12, 15, 25, 30};: This line declares an array of integer with 5 elements. -
int *ptr = arr;: This line declares a pointer variable named 'ptr' (an asterisk '*' is used before the variable name) and initializes the variable with the array name 'arr'. Here, the name of the array (arr) points to the first element of the array. -
printf("The first element of the array: %d\n", *ptr);: This line prints the first element of the array using pointer 'ptr' variable. -
ptr++;The pointer ptr is incremented. Since 'ptr' is an integer, incrementing it by 1 moves the pointer to the next element in the array. Now, incremented 'ptr' points to the second element of the array. -
printf("The second element of the array: %d", *ptr);: This line prints the second element of the array using pointer 'ptr' variable.
Modifying Array Elements Using a Pointer
A pointer can be used to modify the array elements as demonstrated in the following example:
Example of modifying array elements using a pointer
xxxxxxxxxx#include <stdio.h>int main() { int arr[] = {55, 12, 15, 25, 30}; int *ptr = arr; // Pointer pointing to the first element of the array printf("The third element of the array: %d\n", arr[2]); *(ptr + 2) = 65; //Third element of the array modified printf("The modified third element of the array: %d", arr[2]); return 0;}Output of the above example
The third element of the array: 15 The modified third element of the array: 65
Explanation of code:
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int arr[] = {55, 12, 15, 25, 30};: This line declares an array of integer with 5 elements. -
int *ptr = arr;: This line declares a pointer variable named 'ptr' (an asterisk '*' is used before the variable name) and initializes the variable with the array name 'arr'. The name of the array (arr) points to the first element of the array. -
printf("The third element of the array: %d\n", arr[2]);: This line prints the third element of the array. -
*(ptr + 2) = 65;: The line modifies the third element of the array by assigning new value '65'. Here the pointer 'ptr' is incremented by 2 to point the third element of the array. Now, the incremented 'ptr' points to the third element of the array. -
printf("The modified third element of the array: %d", arr[2]);: This line prints the modified third element of the array.
Passing an Array to a Function Using a Pointer
An array can be passed to a function by passing a pointer to its first element as demonstrated in the following example.
Example of passing an array to a function using a pointer
xxxxxxxxxx#include <stdio.h>void printArray(int *ptr, int size) { for (int i = 0; i < size; i++) { printf("%d\n", *(ptr + i)); }}int main() { int numbers[] = {55, 12, 15, 25, 30}; int size = sizeof(numbers) / sizeof(numbers[0]); printArray(numbers, size); return 0;}Output of the above example
55 12 15 25 30
Explanation of code:
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void printArray(int *ptr, int size): This line defines a function name 'printArray' with pointer parameter '*ptr' and another parameter 'size'. -
for (int i = 0; i < size; i++): This is a for loop inside the function. -
printf("%d\n", *(ptr + i));: This prints the value the pointer points to. The pointer is incremented by adding loop variable 'i'. -
int numbers[] = {55, 12, 15, 25, 30};: This line initializes an array of integer named 'numbers' with 5 elements. -
int size = sizeof(numbers) / sizeof(numbers[0]);: This find the length of the 'numbers' array. -
printArray(numbers, size);: This calls the function 'printArray'. Here the array 'numbers' is passed to the function. When an array is passed to a function, what actually gets passed is a pointer to the first element of the array.
