Basic Introduction to C: Structs, Pointers and Dynamic Memory

In this second part of the C programming introduction, we explore the core features that give C its efficiency and control: Structs, Pointers, and Dynamic Memory Management.

---

1. Structs & typedef

A struct allows you to group related variables under a single name:

#include <stdio.h>

typedef struct Point {
    int x;
    int y;
} Point;

int main() {
    Point p1 = {10, 20};
    printf("Point coordinates: (%d, %d)\n", p1.x, p1.y);
    return 0;
}

Using typedef simplifies syntax so you can write Point p1; instead of struct Point p1;.

---

2. Pointers & Memory Addresses

A pointer is a variable that stores the memory address of another variable.

• &var: Returns the memory address of var.
• *ptr: Dereferences ptr to access or modify the value stored at that address.

#include <stdio.h>

int main() {
    int val = 42;
    int *ptr = &val; // ptr holds address of val

    printf("Value: %d\n", val);
    printf("Address: %p\n", (void*)ptr);
    printf("Value via pointer: %d\n", *ptr);

    *ptr = 100; // Modifies val directly
    printf("New value: %d\n", val);
    return 0;
}

---

3. Dynamic Memory Allocation (malloc & free)

When the size of data isn’t known at compile time, we allocate memory on the Heap using stdlib.h:

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

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

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

    for (int i = 0; i < n; i++) {
        arr[i] = (i + 1) * 10;
    }

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

    // Always free allocated memory to prevent memory leaks!
    free(arr);
    return 0;
}

Understanding pointers and memory safety is essential for low-level systems programming and C software development.