直接复制吧

#include<iostream>
#include<stack>
using namespace std;
bool is_limited_char(char c){
    return c=='+'||c=='-'||c=='*'||c=='/'||c=='('||c==')';
}
bool is_limited_alpha(char a){
    return a>96&&a<100;
}
bool is_limited_calculation(char d){
    return d=='+'||d=='-'||d=='*'||d=='/';
}
stack<char> s;
int main(){
    char c,lc='\0';
    while(cin>>c){
        if(c==';')break;
        if(is_limited_alpha(c)&&is_limited_alpha(lc)||
            is_limited_calculation(c)&&is_limited_calculation(lc)){
            cout<<"ERROR 3"<<endl;
            return 0;
        }
        if(c=='(')s.push('(');
        if(c==')'){
            if(s.empty()){
                cout<<"ERROR 2"<<endl;
                return 0;
            }
            else s.pop();
        }
        if(!is_limited_char(c)&&!is_limited_alpha(c)){
            cout<<"ERROR 1"<<endl;
            return 0;
        }
        lc=c;
    }
    if(!s.empty()){
        cout<<"ERROR 2"<<endl;
        return 0;
    }
    else{
        cout<<"OK"<<endl;
        return 0;
    }
}