方程求解2,3样例过不去！

自己查不出问题

求各位大佬帮帮忙

QwQ

#include<iostream>
using namespace std;
char op;
int read(){
    int num=0;
    char ch;
    while('0' > ch || ch > '9'){
        cin >>ch;
    }
    while('0' <= ch && ch <= '9'){
        num=num*10+ch-'0';
        cin >>ch;
    }
    op=ch;
    if(ch == '?'){
        cin>>op; 
        while(op==' ' && op != EOF){
            cin>>op;
        }
        return -1;
    } 
    while(op==' ' && op != EOF){
        cin>>op;
    }
    return num;
}
int main(){
    char t;
    int  x,y,z,f=1,a; 
    x=read();
    t=op;
    y=read();
    if(t == '-'){
        f=-1;
    }
    if(y == -1){
        a=y;
        y=x;
        x=a;
    }
    if(x == -1){
        z=read();
        cout<<z-f*x;
        return 0;
    }
    cout<<x+f*y;
    return 0; 
}