Expression Evaluation

#include<bits/stdc++.h>
using namespace std;
int priority(char c){
    if(c=='*'||c=='/') return 1;
    else return 0;
}
int output(int a, int b, char c){
    if(c=='+')
        return a+b;
    else if(c=='-')
        return a-b;
    else if(c=='*')
        return a*b;
    else if(c=='/')
        return a/b;
}
int evaluateEquation(string equ){
    stack<int> numbers;
    stack<char> opa;
    int num=0;
    for(int i=0;i<equ.size();i++){
        if(equ[i]>='0'&&equ[i]<='9'){
            num=num*10+(equ[i]-48);
        }
        else{
            numbers.push(num);
            num=0;
            while(!opa.empty()&&priority(opa.top())>=priority(equ[i])){
                int b=numbers.top();
                numbers.pop();
                int a=numbers.top();
                numbers.pop();
                int res=output(a, b, opa.top());
                //cout<<res<<endl;
                opa.pop();
                numbers.push(res);
            }
            opa.push(equ[i]);
        }
    }
    if(num!=0)
        numbers.push(num);
    while(!opa.empty()){
        int b=numbers.top();
        numbers.pop();
        int a=numbers.top();
        numbers.pop();
        int res=output(a, b, opa.top());
        opa.pop();
        numbers.push(res);
    }
    return numbers.top();
}
int main(){
    string equ;
    cin>>equ;
    cout<<evaluateEquation(equ)<<endl;
}