大数加法

 1 #include <string>
 2 #include <iostream> 
 3 using namespace std;
 4 
 5 string add(string s1,string s2);
 6 int carry;
 7 
 8 int main()
 9 {
10    string a,b;
11    int T,i,j,k=1; 
12    cin>>T;
13        do
14        {
15           cin>>a>>b;
16           cout<<"Case "<<k++<<":"<<endl;
17           cout<<a<<" + "<<b<<" = "<<add(a,b)<<endl;     
18        }while(--T);
19         
20    //system("pause");    
21    return 0;
22 }
23 
24 string add(string s1,string s2)
25 {
26    string s;
27    string::size_type i,j;
28    int t,carry,len1,len2;
29    
30    if(s1.length() < s2.length())
31    {
32      s = s1;
33      s1 = s2;        
34      s2 = s;
35    }     
36    len1 = s1.length();
37    len2 = s2.length();
38 
39     carry = 0;
40     for(i = len1-1 ,j = len2-1; j != string::npos ; --i,--j)
41     {
42        t =s1[i]-'0' + s2[j]-'0'+carry;
43        s1[i] ='0'  + t%10;
44        carry = t/10;
45     }
46     
47     if(carry)
48     for(j = i ; j != string::npos; --j)
49     {
50       t = s1[j]-'0'+carry;
51       s1[j] = '0' +t%10;
52       carry = t/10; 
53     }
54     if(carry)  s1.insert(0,1,'1'); 
55     return s1;    
56 }