Pointers and Arrays

Arrays and pointers are closely related in C programming. In fact, they're so connected that understanding their relationship is crucial for mastering C!

Array Names as Pointers

When you declare an array, the array name acts as a pointer to the first element of the array. Think of it like this: if your array is a row of houses, the array name is the address of the first house.

int numbers[5] = {10, 20, 30, 40, 50};
// 'numbers' points to the address of numbers[0]

Pointer Arithmetic with Arrays

You can use pointer arithmetic to navigate through array elements:

#include <stdio.h>

int main() {
    int arr[5] = {1, 2, 3, 4, 5};
    int *ptr = arr;  // ptr points to first element
    
    printf("First element: %d\n", *ptr);        // Output: 1
    printf("Second element: %d\n", *(ptr + 1)); // Output: 2
    printf("Third element: %d\n", *(ptr + 2));  // Output: 3
    
    return 0;
}

Array Subscript vs Pointer Notation

These two notations are equivalent in C:

Array Notation	Pointer Notation	Description
arr[0]	*arr or *(arr + 0)	First element
arr[1]	*(arr + 1)	Second element
arr[i]	*(arr + i)	i-th element

#include <stdio.h>

int main() {
    int data[4] = {100, 200, 300, 400};
    
    // Both ways access the same elements
    printf("Using array notation: %d\n", data[2]);     // Output: 300
    printf("Using pointer notation: %d\n", *(data + 2)); // Output: 300
    
    return 0;
}

Passing Arrays to Functions

When you pass an array to a function, you're actually passing a pointer to the first element:

#include <stdio.h>

void printArray(int *arr, int size) {
    for(int i = 0; i < size; i++) {
        printf("%d ", arr[i]);  // or *(arr + i)
    }
    printf("\n");
}

int main() {
    int numbers[5] = {5, 10, 15, 20, 25};
    
    printArray(numbers, 5);  // Pass array to function
    
    return 0;
}

Dynamic Memory and Arrays

You can create arrays dynamically using pointers and malloc():

#include <stdio.h>
#include <stdlib.h>

int main() {
    int size = 5;
    int *dynamicArray = (int*)malloc(size * sizeof(int));
    
    // Fill the array
    for(int i = 0; i < size; i++) {
        dynamicArray[i] = i * 10;
    }
    
    // Print the array
    for(int i = 0; i < size; i++) {
        printf("%d ", dynamicArray[i]);
    }
    
    free(dynamicArray);  // Don't forget to free memory!
    return 0;
}

Key Points to Remember

• Array names are pointers to the first element
• arr[i] is equivalent to *(arr + i)
• When passing arrays to functions, you're passing pointers
• Pointer arithmetic allows you to navigate through array elements
• Dynamic arrays are created using pointers and memory allocation functions

Understanding the relationship between pointers and arrays opens up powerful programming techniques and helps you write more efficient C code!