[51NOD]大数加法（模拟）

题目链接：http://www.51nod.com/onlineJudge/questionCode.html#!problemId=1005

要处理符号，还要特别注意0和连续进位等情况。偷懒使用strcmp，但是前提必须是长度相等，否则是字典序。

 #include <algorithm>
 #include <iostream>
 #include <iomanip>
 #include <cstring>
 #include <climits>
 #include <complex>
 #include <fstream>
 #include <cassert>
 #include <cstdio>
 #include <bitset>
 #include <vector>
 #include <deque>
 #include <queue>
 #include <stack>
 #include <ctime>
 #include <set>
 #include <map>
 #include <cmath>

 using namespace std;

 const int maxn = ;
 char ca[maxn], cb[maxn], cs[maxn];

 void add(char* ca, char* cb) {
     int a[maxn];
     int b[maxn];
     memset(a, , sizeof(a));
     memset(b, , sizeof(b));
     int la = strlen(ca);
     int lb = strlen(cb);
     for(int i = ; i < la; i++) a[i] = ca[la-i-] - '';
     for(int i = ; i < lb; i++) b[i] = cb[lb-i-] - '';
     for(int i = ; i < maxn; i++) {
         a[i] += b[i];
         a[i+] += a[i] / ;
         a[i] %= ;
     }
     int p = maxn;
     while(p--) if(a[p] != ) break;
     for(int i = p; i >= ; i--) printf("%d", a[i]);
     printf("\n");
 }

 void sub(char* ca, char* cb) {
     int a[maxn];
     int b[maxn];
     memset(a, , sizeof(a));
     memset(b, , sizeof(b));
     int la = strlen(ca);
     int lb = strlen(cb);
     for(int i = ; i < la; i++) a[i] = ca[la-i-] - '';
     for(int i = ; i < lb; i++) b[i] = cb[lb-i-] - '';
     for(int i = ; i < la; i++) {
         if(a[i] >= b[i]) a[i] -= b[i];
         else {
             a[i] = a[i] - b[i] + ;
             a[i+]--;
         }
     }
     int p = maxn;
     while(p--) if(a[p] != ) break;
     for(int i = p; i >= ; i--) printf("%d", a[i]);
     printf("\n");
 }

 int main() {
     // freopen("in", "r", stdin);
     memset(ca, , sizeof(ca));
     memset(cb, , sizeof(cb));
     scanf("%s %s", ca, cb);
     int la = strlen(ca);
     int lb = strlen(cb);
     if(ca[] == '' && cb[] == '') printf("0\n");
     else if(ca[] == '-' && cb[] == '-') {
         printf("-");
         add(ca+, cb+);
     }
     else if(ca[] != '-' && cb[] != '-') add(ca, cb);
     else if(ca[] == '-' && cb[] != '-') {
         if(la -  < lb) sub(cb, ca+);
         else if(strcmp(ca+, cb) > ) {
             printf("-");
             sub(ca+, cb);
         }
         else if(strcmp(ca+, cb) == ) printf("0\n");
         else sub(cb, ca+);
     }
     else if(ca[] != '-' && cb[] == '-') {
         if(la -  < lb) sub(ca, cb+);
         else if(strcmp(ca, cb+) > ) sub(ca, cb+);
         else if(strcmp(ca, cb+) == ) printf("0\n");
         else {
             printf("-");
             sub(cb+, ca);
         }
     }
     return ;
 }