北大acm 1001 Exponentiation

#include<stdio.h>
#include<string.h>
#include<iostream>
using namespace std;
void mul(int *c,int *a,int *b)  //c=a*b
{
    int i,j,k,carry,result;
    memset(c,0,sizeof(int)*126);
    for(j=0,carry=0;j<b[124];j++)
        {
        for(i=0;i<a[124];i++)
        {
                        k=i+j;
            result=b[j]*a[i]+carry+c[k];
            c[k]=result%10;
            carry=result/10;
        }
                while(carry)
                {
                        k++;
                        result=carry+c[k];
                        carry=result/10;
                        c[k]=result%10;
                }
        }
    for(i=123;c[i]==0;i--)
        c[124]=i;
    c[125]=a[125]+b[125];
}
void s2i(char *str,int *a)
{
        int n=strlen(str),i,j;
        char tmp;
        for(i=0,j=n-1;i<j;i++,j--)
        {
                tmp=str[i];
                str[i]=str[j];
                str[j]=tmp;
        }
        for(i=0,a[125]=a[124]=0;str[i]!='.';i++)
        {
                        a[i]=str[i]-'0';
                        a[125]++;
        }
        for(i++;i<n;i++)
                a[i-1]=str[i]-'0';
        a[124]=n-1;

}
int main()
{
    int a[126],b[126],c[126],n; //R[125]用来保存小数点,R[124]保存长度
    char str[10];
    while(cin>>str>>n)
    {
        s2i(str,a);
        memcpy(b,a,126*sizeof(int));
        memset(c,0,126*sizeof(int));
        c[0]=1;
        c[124]=1;
        for(int i=1;i<=n;i++)
                {
            mul(b,c,a);
                        memcpy(c,b,126*sizeof(int));
                }
        //output
        int i=c[124]-1,j=c[124]-c[125],k;
        for(k=0;c[k]==0;k++)
            ;
        if(j<0)
        {
            printf(".");
            while(j<0)
            {
                printf("0");
                j++;
            }
            while(i>=k)
            {
                printf("%d",c[i]);
                i--;
            }
        }
        else
        {
            while(i>=k)
            {
                if(j==0)
                    printf(".");
                j--;
                printf("%d",c[i]);
                                i--;
            }
        }
        printf("\n");
    }
    return 0;
}