帮你把代码该了，可以ac 了
#define N 1000
#include<stdio.h>
#include<string.h>
int main(){
	char str[7];
	int n=0;
	char aResult[N];
	int i,j,k,beffect,startcpy;
	char Cpystr[7];
	int mulp1[N]={0},mulp2[N]={0},digitstr[N]={0};
	int len=0;
	int number=0,number1=0;
	aResult[N-1]='\0';

	while(scanf("%s%d",str,&n)!=EOF){
		memset(aResult,'0',sizeof(aResult)-1);
		memset(Cpystr,'0',sizeof(Cpystr)-1);
		memset(mulp1,0,sizeof(mulp1)-1);
		memset(mulp2,0,sizeof(mulp2)-1);
		memset(digitstr,0,sizeof(digitstr)-1);

	        beffect=0;
		number=0;
		for(i=0;i<6;i++){
			if(beffect && str[i]!='.')
				Cpystr[number++]=str[i];
			else if(str[i]>'0'){
				Cpystr[number++]=str[i];
				beffect=1;
			}	
		}

		for(i=number-1,j=0;i>=0;i--,j++)
			digitstr[j]=Cpystr[i]-'0';
		
		i=0;
		while(str[i++]!='.');
		len=n*(6-i);
		
		for(i=0;i<number;i++)
			mulp1[i]=digitstr[i];

		number1=number;	
		for(i=0;i<n-1;i++){
			for(j=0;j<number;j++)
				for(k=0;k<number1;k++)
					mulp2[j+k]+=digitstr[j]*mulp1[k];

			number1=number1+number;
			for(j=0;j<=number1;j++)
				if(mulp2[j]>=10){
					mulp2[j+1]+=mulp2[j]/10;
					mulp2[j]=mulp2[j]%10;
				}

			for(j=0;j<=number1;j++)
				mulp1[j]=mulp2[j];

			memset(mulp2,0,sizeof(mulp2)-1);
		}

		startcpy=0;
		for(j=N-2,k=0;j>=0&&k<N;k++){
			if(len>=0) len--;
			if(len==-1 && startcpy==1){
				aResult[j--]='.';
				k--;
				len=-2;
				continue;
			}
			if(startcpy==1 ||len==-1)
				aResult[j--]=mulp1[k]+'0';
			else if(mulp1[k]>0){
				aResult[j--]=mulp1[k]+'0';
				startcpy=1;
				
			}
				
		}

		j=0;
		while(aResult[j++]!='.')
			if(aResult[j-1]>'0') break;
		puts(aResult+j-1);

	}
	return 0;
}