大数相加，这个写的相当给力，可以模仿

#include<iostream>
using namespace std;
#include<vector>//要用到vector
#include<string>//要用到string
#include<algorithm>//要用到reverse
int main(int argc,char *argv[])
{
    string sa,sb,t;//sa表示第一个加数。sb表示第二个加数。t是临时变量，即如果sa.size()<sb.size(),交换sa和sb
    vector<int> v;//存贮每位的和
    int a,b,sum;//a表示sa的某一位,b表示sb的某一位,sum表示它们的和
    int flag;//进位标志
    while(cin>>sa>>sb)
    {
        flag=0;
        v.clear();//每次清除
        sum=0;
        reverse(sa.begin(),sa.end());
        reverse(sb.begin(),sb.end());
        //如果sb的长度大于sa，则交换
        if(sa.size()<sb.size())
        {
            t=sa;
            sa=sb;
            sb=t;
        }
        int i;
        for(i=0;i<sa.size();i++)
        {
            if(sa[i]=='0')
            {
                a=0;
            }
            else if(sa[i]=='1')
            {
                a=1;
            }
            else if(sa[i]=='2')
            {
                a=2;
            }
            else if(sa[i]=='3')
            {
                a=3;
            }
            else if(sa[i]=='4')
            {
                a=4;
            }
            else if(sa[i]=='5')
            {
                a=5;
            }
            else if(sa[i]=='6')
            {
                a=6;
            }
            else if(sa[i]=='7')
            {
                a=7;
            }
            else if(sa[i]=='8')
            {
                a=8;
            }
            else if(sa[i]=='9')
            {
                a=9;
            }
            else if(sa[i]=='a')
            {
                a=10;
            }
            else if(sa[i]=='b')
            {
                a=11;
            }
            else if(sa[i]=='c')
            {
                a=12;
            }
            else if(sa[i]=='d')
            {
                a=13;
            }
            else if(sa[i]=='e')
            {
                a=14;
            }
            else if(sa[i]=='f')
            {
                a=15;
            }
            else if(sa[i]=='g')
            {
                a=16;
            }
            else if(sa[i]=='h')
            {
                a=17;
            }
            else if(sa[i]=='i')
            {
                a=18;
            }
            else if(sa[i]=='j')
            {
                a=19;
            }
            if(i>=sb.size())
            {
                b=0;
            }
            else
            {
                if(sb[i]=='0')
                {
                    b=0;
                }
                else if(sb[i]=='1')
                {
                    b=1;
                }
                else if(sb[i]=='2')
                {
                    b=2;
                }
                else if(sb[i]=='3')
                {
                    b=3;
                }
                else if(sb[i]=='4')
                {
                    b=4;
                }
                else if(sb[i]=='5')
                {
                    b=5;
                }
                else if(sb[i]=='6')
                {
                    b=6;
                }
                else if(sb[i]=='7')
                {
                    b=7;
                }
                else if(sb[i]=='8')
                {
                    b=8;
                }
                else if(sb[i]=='9')
                {
                    b=9;
                }
                else if(sb[i]=='a')
                {
                    b=10;
                }
                else if(sb[i]=='b')
                {
                    b=11;
                }
                else if(sb[i]=='c')
                {
                    b=12;
                }
                else if(sb[i]=='d')
                {
                    b=13;
                }
                else if(sb[i]=='e')
                {
                    b=14;
                }
                else if(sb[i]=='f')
                {
                    b=15;
                }
                else if(sb[i]=='g')
                {
                    b=16;
                }
                else if(sb[i]=='h')
                {
                    b=17;
                }
                else if(sb[i]=='i')
                {
                    b=18;
                }
                else if(sb[i]=='j')
                {
                    b=19;
                }
            }
            sum=a+b+flag;
            if(sum>19)
            {
                flag=1;
                sum=sum-20;
            }
            else
            {
                flag=0;
            }
            v.push_back(sum);
        }
        if(flag==1)
        {
            v.push_back(1);
        }
        for(i=v.size()-1;i>=0;i--)
        {
            if(v[i]<10)
            {
                cout<<v[i];
            }
            else if(v[i]==10)
            {
                cout<<'a';
            }
            else if(v[i]==11)
            {
                cout<<'b';
            }
            else if(v[i]==12)
            {
                cout<<'c';
            }
            else if(v[i]==13)
            {
                cout<<'d';
            }
            else if(v[i]==14)
            {
                cout<<'e';
            }
            else if(v[i]==15)
            {
                cout<<'f';
            }
            else if(v[i]==16)
            {
                cout<<'g';
            }
            else if(v[i]==17)
            {
                cout<<'h';
            }
            else if(v[i]==18)
            {
                cout<<'i';
            }
            else if(v[i]==19)
            {
                cout<<'j';
            }
        }
        cout<<endl;
    }
    return 0;
}