> /*考虑大数乘法和大数乘幂.
> 大数乘法我没有优化,达到了0(n^2)
> 大数乘幂优化了一下，x^n= x*(x^2)*(x^4)*....  ()内的为临时计算项
> 另外需要注意底数为0和整数的时候，没有考虑负数。 指数也不考虑0和负数。*/
> /*cacluate R^n accurately*/
> #include <stdio.h>
> 
> #define MAX_DIGITS	180
> 
> int NumOut[MAX_DIGITS];
> int NumIn1[MAX_DIGITS];
> int NumIn2[MAX_DIGITS];
> 
> int StringToDecimal(char *pStr,int *pNum,int *pLength);
> int LargeIntegerMultiply(int *pNum1,int len1,int *pNum2,int len2,int *pNumOut);
> int LargeIntegerPow(int *pNumIn,int lenIn,int exp,int *pNumOut);
> 
> int main(void)
> {
> 	char string[6];
> 	int exponent,length,decimalbits,beginprint;
> 	int i,j;
> 
> 	while(scanf("%s %d",string,&exponent)!=EOF){
> 		//convert the string to integer
> 		decimalbits = StringToDecimal(string,NumIn1,&length);
> 		//process 0
> 		if((length==1) &&(NumIn1[0]==0)){
> 			printf("0\r\n");			
> 			continue;
> 		}
> 
> 		length=LargeIntegerPow(NumIn1,length,exponent,NumOut);			
> 		decimalbits *= exponent;
> 		
> 		//output the interger part
> 		i=length-1;
> 		if(length>decimalbits){
> 			beginprint=0;
> 			while(i>=decimalbits){
> 				if((NumOut[i]!=0)||(beginprint==1)){	//omit the prefix 0s
> 					beginprint=1;
> 					printf("%d",NumOut[i]);
> 				}
> 				--i;		
> 			}
> 		}
> 		//output the decimal part
> 		if(decimalbits!=0){
> 			printf(".");
> 			//we need to remove the trailing 0s
> 			//find trailing 0's num
> 			j=0;
> 			while(NumOut[j]==0){
> 				++j;
> 			}	
> 			while(i>=j){
> 				printf("%d",NumOut[i]);
> 				--i;
> 			}
> 		}
> 		printf("\r\n");
> 	}
> 	return 0;
> }
> 
> int StringToDecimal(char *pStr,int *pNum,int *pLength)
> {
> 	int decimalbits,beginexp,isZero,isInteger;
> 	int k,tmp;
> 	int bits=0;
> 
> 	beginexp = 0;
> 	decimalbits = 0;
> 	while(*pStr){
> 		if(*pStr=='.'){
> 			beginexp=1;	
> 		}else{
> 			pNum[bits]=*pStr-'0';	//convert to digit
> 			++bits;
> 			if(beginexp){
> 				++decimalbits;
> 			}
> 		}
> 		++pStr;
> 	}
> 	
> 	//reverse the num bits order
> 	k=0;	
> 	while(k<(bits>>1)){
> 		tmp = pNum[k];
> 		pNum[k]=pNum[bits-1-k];
> 		pNum[bits-1-k]=tmp;
> 		++k;
> 	}
> 	
> 	//check whether the decimal part is needed???
> 	isZero=1;
> 	isInteger=1;
> 	for(k=0;k<decimalbits;++k){
> 		if(pNum[k]!=0){
> 			isInteger=0;
> 			isZero=0;
> 			break;
> 		}
> 	}
> 	if(isInteger==1){
> 		for(k=decimalbits;k<bits;++k){
> 			if(pNum[k]!=0){
> 				isZero=0;
> 				break;
> 			}
> 		}
> 	}
> 
> 	if(isZero==1){
> 		*pLength=1;	//only one value 0
> 		pNum[0]=0;
> 		decimalbits=0;	//no decimal part
> 	}else if(isInteger==1){
> 		*pLength=bits-decimalbits;
> 		for(k=decimalbits;k<bits;++k){
> 			pNum[k-decimalbits]=pNum[k];
> 		}
> 		decimalbits=0;
> 	}else{
> 		*pLength=bits;
> 	}
> 	return decimalbits;
> }
> 
> int LargeIntegerMultiply(int *pNum1,int len1,int *pNum2,int len2,int *pNumOut)
> {
> 	int i,j;
> 	for(i=0;i<len1+len2;++i){	//clear the output num
> 		pNumOut[i]=0;
> 	}
> 	for(i=0;i<len1;++i){
> 		for(j=0;j<len2;++j){
> 			pNumOut[i+j] += pNum1[i]*pNum2[j];
> 		}
> 	}
> 	for(i=0;i<len1+len2-1;++i){
> 		if(pNumOut[i]>=10){
> 			pNumOut[i+1] += pNumOut[i]/10;
> 			pNumOut[i] %= 10;
> 		}
> 	}
> 	if(pNumOut[len1+len2-1]!=0)
> 		return len1+len2;
> 	else
> 		return len1+len2-1;
> }
> 
> //Notice: all the numbers should be non-negative
> int LargeIntegerPow(int *pNumIn,int lenIn,int exp,int *pNumOut)
> {
> 	int i,j;
> 	int lenOut;
> 	int *pNumIn2 = NumIn2;
> 
> 	lenOut=1;
> 	pNumOut[0]=1;
> 	while(exp!=0){
> 		if(exp & 0x01){
> 			lenOut=LargeIntegerMultiply(pNumOut,lenOut,pNumIn,lenIn,pNumIn2);
> 			for(i=0;i<lenOut;++i){
> 				pNumOut[i]=pNumIn2[i];
> 			}
> 		}
> 		if(exp!=1){
> 			lenIn=LargeIntegerMultiply(pNumIn,lenIn,pNumIn,lenIn,pNumIn2);
> 			for(i=0;i<lenIn;++i){
> 				pNumIn[i]=pNumIn2[i];
> 			}
> 		}
> 		exp >>=1;
> 	}
> 	return lenOut;
> }