What is a Pointer in C?

A pointer is a variable that stores the memory address of another variable. Pointers are the defining feature of C, providing low-level hardware memory access, efficient pass-by-reference semantics, and dynamic heap allocation.

Address-of (&) and Dereference (*) Operators

• &variable: Returns the hexadecimal memory address where the variable is located in RAM.
• *pointer: Dereferences the pointer, accessing or mutating the value stored at that address.

c (ISO Standard)
Run in Compiler.cCopy
#include <stdio.h>

int main() {
    int value = 42;
    int *ptr = &value; /* ptr holds the memory address of value */

    printf("Value: %d\n", value);
    printf("Memory Address of value (&value): %p\n", (void*)&value);
    printf("Pointer Address (ptr): %p\n", (void*)ptr);
    printf("Dereferenced Pointer (*ptr): %d\n", *ptr);

    /* Modifying value via pointer dereference */
    *ptr = 99;
    printf("Updated value after *ptr = 99: %d\n", value);

    return 0;
}

Pointer Arithmetic

When you add or subtract integers from a pointer, C scales the operation by the byte size of the pointed-to data type (sizeof(*ptr)):

c (ISO Standard)
Run in Compiler.cCopy
#include <stdio.h>

int main() {
    int arr[3] = {100, 200, 300};
    int *ptr = arr; /* points to arr[0] */

    printf("First element via pointer: %d\n", *ptr);
    printf("Second element via *(ptr + 1): %d\n", *(ptr + 1));
    printf("Third element via *(ptr + 2): %d\n", *(ptr + 2));

    return 0;
}

Dynamic Memory Allocation (malloc and free)

Heap memory is allocated manually at runtime using <stdlib.h>:

c (ISO Standard)
Run in Compiler.cCopy
#include <stdio.h>
#include <stdlib.h>

int main() {
    int n = 5;
    int *dynamicArray = (int *)malloc(n * sizeof(int));

    if (dynamicArray == NULL) {
        printf("Memory allocation failed!\n");
        return 1;
    }

    for (int i = 0; i < n; i++) {
        dynamicArray[i] = (i + 1) * 10;
        printf("dynamicArray[%d] = %d\n", i, dynamicArray[i]);
    }

    /* Always release dynamically allocated heap memory */
    free(dynamicArray);
    dynamicArray = NULL;

    return 0;
}

Related C Tutorials & Practical Examples

• Connect arrays and pointer decay in Arrays in C Programming.
• Practice pointer passing with our Swap Two Numbers in C Example.
• Step through pointer addresses visually in our Online C Debugger.