Case 1:
1 + 2 = 3

Case 2:
112233445566778899 + 998877665544332211 = 1111111111111111110

 1 #include<iostream>
 2 #include<cstring>
 3 #include<string>
 4 using namespace std;
 5 string bigAdd(string num1, string num2) {
 6 
 7     string res;
 8     if (num1.size() == 0) {
 9         res = num2;
10         return res;
11     }
12     if (num2.size() == 0) {
13         res = num1;
14         return res;
15     }
16 
17     res = "";
18     int n1 = num1.size()-1, n2 = num2.size()-1;
19     int carry = 0;
20     while (n1 >= 0 || n2 >= 0) {
21 
22         int a = n1 >= 0 ? num1[n1--] - ‘0‘ : 0;
23         int b = n2 >= 0 ? num2[n2--] - ‘0‘ : 0;
24 
25         int t = carry + a + b;
26         carry = t / 10;
27         t = t % 10;
28         res = to_string(t) + res;
29     }
30     //判断是否还有进位
31     while (carry) {
32         int t = carry / 10;
33         carry %= 10;
34         res = to_string(carry) + res;
35         carry = t;
36     }
37     return res;
38 }
39 
40 int main() {
41     int sum=0,count;
42     cin>>count;
43     if(count>=1&&count<=20) {
44         string a[22][2];
45         for(int i=0; i<count; i++) {
46             cin>>a[i][0]>>a[i][1];
47         }
48         for(int i=0; i<count; i++) {
49             cout<<"Case "<<i+1<<":"<<endl;
50             cout<<a[i][0]<<" + "<<a[i][1]<<" = "<<bigAdd(a[i][0],a[i][1])<<endl;
51             if(i+1!=count) {
52                 cout<<endl;
53             }
54         }
55     }
56     return 0;
57 }