Помогите пожалуйста написать программу на C

#include <stdio.h>
#include <stdlib.h>
#include <assert.h>
#define BUFFER 256
unsigned long long fact(unsigned long long n) {
assert(n <= 20);
return n == 0? 1 : n * fact(n - 1);
}
int main(void) {
unsigned long long n;
scanf_s("%llu", &n);
printf("%llu\n", fact(n));
system("pause > nul");
return 0;
}

#include <iostream>
using namespace std;
void swap(int *a, int i, int j)
{
int s = a[i];
a[i] = a[j];
a[j] = s;
}
bool NextSet(int *a, int n)
{
int j = n - 2;
while (j != -1 && a[j] >= a[j + 1]) j--;
if (j == -1)
return false;
int k = n - 1;
while (a[j] >= a[k]) k--;
swap(a, j, k);
int l = j + 1, r = n - 1;
while (l<r)
swap(a, l++, r--);
return true;
}
void Print(int *a, int n)
{
static int num = 1;
cout.width(3);
cout << num++ << ": ";
for (int i = 0; i < n; i++)
cout << a[i] << " ";
cout << endl;
}
int main()
{
int n, *a;
cout << "N = ";
cin >> n;
a = new int[n];
for (int i = 0; i < n; i++)
a[i] = i + 1;
Print(a, n);
while (NextSet(a, n))
Print(a, n);
cin.get(); cin.get();
return 0;
}