POJ 1001 Exponentiation 模拟小数幂

模拟小数幂

小数点位 pos

非零末位 e

长度 len

只有三种情况　

　　pos > len

　　pos < e

　　e < pos < len

#include <iostream>
#include <cstring>
using namespace std;
int a[500], b[500], c[500];
void Cal()
{
    memset(c, 0, sizeof(c)); 
    for(int i = 0; i < 200; i++)
        for(int j = 0; j < 10; j++)
            c[i+j] += a[i] * b[j];
    for (int i = 0; i < 200; i++){
        c[i+1] += c[i]/10;
        c[i] %= 10;
    }
    memset(a, 0, sizeof(a));    
    for (int i = 0; i <= 200; i++)
        a[i] = c[i];
}
char s[10];
int pos, n, len;
int main()
{
    while(cin>>s>>n)
    {
        memset(a,0,sizeof(a));
        memset(b,0,sizeof(b));
        memset(c,0,sizeof(c));
        int t = 0;
        for (int i = 5; i >= 0; i--)
        {
            if(s[i]=='.') pos = i;
            else b[t++] = s[i] - '0';
        }
        a[0] = 1;
        for(int i = 1; i <= n; i++) Cal(); 
        len = 200;
        while(!c[len] && len>=0) len--;
        int e = 0;//末尾
        while(!c[e] && e<= len) e++;
        pos = 5 - pos; pos *= n;//小数点 
        if(pos > len)
        {
            cout<<".";
            for (int i = pos-1; i >= e; i--) cout<<c[i];
            cout<<endl;
        }
        else if(pos <= e)//整数 
        {
            for (int i = len; i >= pos; i--) cout<<c[i];
            cout<<endl;
        }
        else//普通 
        {
            for (int i = len; i >= pos; i--) cout<<c[i];
            cout<<".";
            for (int i = pos-1; i >= e; i--) cout<<c[i];
            cout<<endl;
        }
    }
}