http://acm.nyist.net/JudgeOnline/problem.php?pid=111
简单模拟：
#include <iostream>
#include <string>
#include <cstring>
using namespace std;
int gcd(int a,int b)
{
if(a<b)return gcd(b,a);
if(b==0)return a;
return gcd(b,a%b);
}
int lcm(int a,int b)
{
return a*b/gcd(a,b);
}
int main()
{
string s;
int fz1,fm1,fz2,fm2;
char ch;
while(cin>>s)
{
fz1=s[0]-'0';
fm1=s[2]-'0';
fz2=s[4]-'0';
fm2=s[6]-'0';
ch=s[3];
int fm=lcm(fm1,fm2);
fz1=fz1*(fm/fm1);
fz2=fz2*(fm/fm2);
int fz;
if(ch=='+'){
fz=fz1+fz2;
if(fz%fm==0){cout<<fz/fm<<endl;continue;}// 2/1或者4/2这种情况应该直接输出
int tmp=gcd(fz,fm);
fz=fz/tmp;
fm=fm/tmp;
if(fz==fm)cout<<1<<endl;
else
cout<<fz<<"/"<<fm<<endl;
}
else {
fz=fz1-fz2;
if(fz%fm==0){cout<<fz/fm<<endl;continue;}
if(fz==0)cout<<0<<endl;
else {
int tmp;
if(fz<0)
tmp=gcd(-fz,fm);
else tmp=gcd(fz,fm);
fz=fz/tmp;
fm=fm/tmp;
if(fz==fm)cout<<1<<endl; // 1/1这种情况应该输出1
else
cout<<fz<<"/"<<fm<<endl;
}
} }
return 0;
}