高精度运算 大数加法

#include <iostream>
#include <cstring>

using std::cin;
using std::cout;
using std::endl;

char *add( char *s1, char *s2 );
char *reversal_str(char *s);

int main()
{
    char s1[100000],s2[100000];
    while( cin >> s1 >> s2 )
        cout << add(s1,s2) << endl;

    return 0;
}


char *add( char *s1, char *s2 )
{
    reversal_str(s1);   reversal_str(s2);
    char carryBit = '0';
    int len1 = strlen(s1), len2 = strlen(s2);
    int len = len1 > len2 ? len1: len2;

    char result[100000];
    int i = 0;
    for ( i = len1; i != len; ++i )
        s1[i] = '0';
    for ( i = len2; i != len; ++i )
        s2[i] = '0';

    for ( i = 0; i != len; ++i ){
        result[i] = (s1[i] + s2[i] + carryBit - 3*'0')%10 + '0';
        carryBit  = (s1[i] + s2[i] + carryBit - 3*'0')/10 + '0';
    }
    if ('0' != carryBit)
        result[i] = carryBit;
    return reversal_str(result);
}

char *reversal_str(char *s)
{
    int len = strlen(s);
    for ( int i = 0; i != len/2; ++i ){
        char temp;
        temp = s[i];
        s[i] = s[len - 1 - i];
        s[len - 1 - i] = temp;
    }
    return s;
}