我用c++ stl解決了此問題。

編譯器：G++(vc++6.0不能通過！)

廢話少說，貼程式碼：

/*
*author:ZhengHaibo
*email:[email protected]
*copyright:ZhengHaibo
*Nanjing University Of Posts and TeleCom.
*/
#include<iostream>  
#include<cstring>  
#include<vector>
using namespace std;
//calculate v1*v2
vector<int> Multi(vector<int> v1,vector<int> v2)
{
   vector<int> vt;//save the result
   for (int i=0;i<v1.size()+v2.size()+1;i++)
   {
	   vt.push_back(0);//Init to 0
   }
   for (int i=0;i<v1.size();i++)
   {
	   for (int j=0;j<v2.size();j++)
	   {
		   vt[i+j]+=v1[i]*v2[j];
		   vt[i+j+1]+=vt[i+j]/10;
		   vt[i+j]%=10;
	   }
   }
   return vt;
}
int main()  
{
	string str;
	int n;
	while(cin>>str>>n){
		vector <int> numArray;
		vector <int> resultArray;
		int dotPos=0,IndexLen;
		IndexLen=str.length()-1;
		//delete 0 in the tail of str. 12.10 ->12.1
		for (int i=str.length()-1;i>=0;i--)
		{
			if(str[i]!='0')
			{
				IndexLen=i;
				break;
			}
		}
		//transform string to vector<int>
        for (int i=IndexLen;i>=0;i--)
        {
			if (str[i]!='.')
			{
				numArray.push_back(str[i]-'0');
			}
			else
				dotPos=IndexLen-i;
        }
		//copy vector
		for (int i=0;i<numArray.size();i++)
		{
			resultArray.push_back(numArray[i]);
		}
		//calculate numArray^n
		for (int j=0;j<n-1;j++)
		{
            resultArray = Multi(resultArray,numArray);
			int len=resultArray.size();
			while (resultArray[len-1]==0)//remove 0 in the big bit
			{
				resultArray.pop_back();
				len--;
			}

		}
		//output the resultArray in prooply way
		if(n*dotPos>=resultArray.size())//if the result is less than 1,the dot pos is out of resultArray
		{
			cout<<".";
			for(int k=0;k<n*dotPos-resultArray.size();k++)
			{
				cout<<"0";
			}
		}
		for (int k=resultArray.size()-1;k>=0;k--)
		{
			if (k==n*dotPos-1)//the dot pos is in resultArray
			{
				if (k!=0)
				{
	                cout<<".";
				}
			}
             cout<<resultArray[k];
		}
		cout<<endl;//if not,Presentation Error!
		//by ZhengHaibo njupt
	}
	return 0;
}

我第一次提交的時候，忘記了每行最後有一個回車，結果顯示“Presentation Error”，加上cout<<endl;就好了。