5.4打卡

#include <bits/stdc++.h>
using namespace std;
unsigned fac(unsigned n)
{
    unsigned f;
    if(n==0)
    f=1;
    else
    f=fac(n-1)*n;
    return f;
}
int main()
{
    unsigned n;
    cout<<"Enter a positive integer: ";
    cin>>n;
    unsigned y=fac(n);
    cout<<n<<"!="<<y<<endl;
    return 0;
}