---
title: "12. Advanced Topics"
description: 'Dynamic memory allocation with malloc/free, recursion, and command-line arguments in C.'
---
- Dynamic memory allocation: `malloc`, `calloc`, `realloc`, `free`
- Recursion
- Command-line arguments (`int main(int argc, char* argv[])`)

## Examples

### Dynamic Memory Allocation (`dynamic_memory.c`)

Creates an array at runtime with `malloc` and frees it when done:

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

int main(void) {
    int n; printf("Enter size: "); scanf("%d", &n);
    int *a = (int*)malloc((size_t)n * sizeof *a);
    if (!a) { perror("malloc"); return 1; }
    for (int i = 0; i < n; i++) a[i] = i;
    for (int i = 0; i < n; i++) printf("%d ", a[i]);
    printf("\n");
    free(a);
    return 0;
}
```

### Recursive Factorial (`factorial_recursive.c`)

Computes N! using recursion, showing base case and recursive step:

```c
#include <stdio.h>

unsigned long long fact(unsigned int n) {
    if (n <= 1) return 1ULL; // base case
    return n * fact(n - 1);  // recursive step
}

int main(void) {
    unsigned int n; printf("Enter n: "); scanf("%u", &n);
    printf("%u! = %llu\n", n, fact(n));
    return 0;
}
```