大数减法（C++实现）

 1 #include<iostream>
 2 #include<cstring>
 3 #include<algorithm>
 4 using namespace std;
 5 const int L=110;
 6 string sub(string a,string b)//只限两个非负整数相加
 7 {
 8 
 9     string ans;
10     int na[L] = {0};
11     int nb[L] = {0};
12     int la = a.size();
13     int lb = b.size();
14     //倒序存储
15     for (int i=0;i<la;i++)
16     {
17         na[la-1-i] = a[i]-‘0‘;
18     }
19     //倒叙存储
20     for (int i=0;i<lb;i++)
21     {
22         nb[lb-i-1] = b[i]-‘0‘;
23     }
24     int lmax = max(la,lb);
25     //从个位开始相减
26     for (int i=0;i<lmax;i++)
27     {
28         na[i] -= nb[i];
29         while (na[i]<0)
30         {
31             na[i] += 10;
32             na[i+1]--;
33         }
34     }
35     //处理前置0
36     while (!na[lmax])
37         lmax--;
38     if (lmax<0)
39         ans = "0";
40     else {
41         for (int i = lmax; i >= 0; i--)
42             ans += na[i] + ‘0‘;
43     }
44     return ans;
45 }
46 int main()
47 {
48     string a,b;
49     while(cin>>a>>b) cout<<sub(a,b)<<endl;
50     return 0;
51 }