这个代码怎么回事?

#include<bits/stdc++.h>
using namespace std;
char ii[1001];
int ans;
int main(){
   cin >> ii;
   int k = strlen(ii);
   for (int i = 1 ; i <= k; i++) 
        if (not('0' <= ii[i] and ii[i] <= '9' and ii[i] >= 'a' and ii[i] <= 'z' and ii[i] >= 'A' and ii[i] <= 'Z')) 
    ans++;   
    cout << ans;
    return 0;
}