整数字符串相加

#include <QtCore/QCoreApplication>
#include <string.h>
#include <QTextCodec>
#include <iostream>
using namespace std;

void SumStr(const string &strA, const string &strB, string &strResult)
{
    //确保左操作数的位数大于右操作数
    int nLeftLen = strA.size();
    int nRightLen = strB.size();
    string strLeft = nLeftLen > nRightLen ? strA : strB;
    string strRight = nLeftLen > nRightLen ? strB : strA;
    nLeftLen = strLeft.size();
    nRightLen = strRight.size();
    strResult.reserve(nLeftLen+1);

    int nTmp = 0;
    char cTmp[2]={0};

    //两数相加
    for(int i=0; i<nRightLen; i++)
    {
        nTmp = strLeft.at(nLeftLen-1-i) - '0' + strRight.at(nRightLen-1-i) - '0' + nTmp;
        cTmp[0] = nTmp%10+'0';
        strResult.insert(0, cTmp);
        nTmp /= 10;
    }

    //相加后进位处理
    int nMin = nRightLen;
    while(0 != nTmp && nMin < nLeftLen)
    {
        nTmp = strLeft.at(nLeftLen-1-nMin) - '0' + nTmp;
        cTmp[0] = nTmp%10+'0';
        strResult.insert(0, cTmp);
        nTmp /= 10;
        ++nMin;
    }

    //左操作数剩下的位数没有参与相加
    if(nMin < nLeftLen)
    {
        string strBub = strLeft.substr(0, nLeftLen-nMin);
        strResult.insert(0, strBub);
    }

    //高位进位
    if(0 != nTmp)
    {
        cTmp[0] = '1';
        strResult.insert(0, cTmp);
    }
}

int main(int argc, char *argv[])
{
    QCoreApplication a(argc, argv);
    QTextCodec::setCodecForTr(QTextCodec::codecForName("gb2312"));
    string strA("8794513");
    string strB("6847897984651");
    string strResult;
    strResult.clear();
    SumStr(strA, strB, strResult);

    cout<<strA << "+" << strB << "= " << strResult.data();

    return a.exec();
}