为什么RE,求解

#include<iostream>
#include<cmath>
#include<cstdio>
#include<cstring>
#include<string>
#include<algorithm>
#include<vector>
#include<stack>
#include<queue>
#include<map> 
#include<bitset>
#include<set>
#include<deque>
#include<iomanip>
using namespace std;
int bf=0,fu=1,chang,xs,de=1;
int ch,le;
double ans;
int main()
{
    while(scanf("%d",&ch))
    {
        scanf("%d",&ch);
        if(ch=='=')
        {
            chang-=bf*fu*de;//最后还有一次未加 
            fu=1;
            bf=0;
            de=-1;
        } 
        if(ch>='0'&&ch<='9')
        {
            bf=bf*10+ch-'0';
            continue;
        } 
        if(ch>='a'&&ch<='z')
        {
            le=ch;
            if(bf==0) bf=1;//系数为1被省略 
            xs+=bf*fu;
            bf=0;
            fu=1;
            continue;
        }
        if(ch=='+')
        {
            chang-=bf*fu*de;
            fu=1;
            bf=0;
            continue;
        }
        if(ch=='-')
        {
            chang-=bf*fu*de;
            bf=0;
            fu=-1;
        }
    }
    chang+=bf*fu*de; ////
    ans=chang/xs;
    printf("%s=%.3lf\n",le,ans);
    return 0;
}