Pointers: Basics & Memory

🔵 C Programming Lesson 7 Intermediate

Pointers are variables that store the memory address of other variables. Pointers are C's most famous and powerful feature, providing direct access to memory layouts.

1 Memory Addresses and Pointer Variables

Every variable exists at a specific location in memory, represented by a hexadecimal address (e.g. `0x7ffeefbff568`). To work with addresses, we use two key operators:

Address-of Operator (`&`): Retrieves the memory address of a variable.
Dereferencing Operator (`*`): Accesses or modifies the value stored at the address a pointer is pointing to.

2 Declaring and Dereferencing Pointers

Let's run a program declaring pointers, displaying addresses, and modifying values via dereferencing:

C — Pointer Basics ▶ Run Code

#include <stdio.h>

int main() {
    int num = 42;
    int *ptr = # // ptr stores the address of num

    // Print values and addresses (%p is format specifier for addresses)
    printf("Value of num: %d\n", num);
    printf("Address of num (&num): %p\n", (void*)&num);
    printf("Value stored in ptr (address): %p\n", (void*)ptr);
    printf("Dereferenced ptr (*ptr): %d\n", *ptr);

    // Modify num's value via the pointer dereference
    *ptr = 99;
    printf("New value of num after *ptr = 99: %d\n", num);

    return 0;
}

3 Code Challenge

Challenge: Write a program that declares a double variable `temp = 36.6`, a pointer pointing to it, and prints the variable's value. Then modify the temperature to `37.2` using dereferencing, and print the updated temperature.