N！的位数

数学规律：

     N！的位数 n =（lg1+lg2+┈┈+lgN）+1;

     对（lg1+lg2+┈┈+lgN）取整数部分；

#include <iostream>#include <cstdio>#include <string>#include <cstdio>#include <cstring>#include <algorithm>#include <iomanip>#include <cmath>using namespace std;int main(){    int n;    while(cin>>n){        double sum=0;        for(int i=1;i<=n;i++)            sum+=log10(i);        cout<<(int)sum+1<<endl;    }    return 0;}