整数的四则运算（一步）

#include <bits/stdc++.h>
using namespace std;
string no1(string);//清除多余空格 
int no2(string,string);//计算
int no3(string,string);//寻找乘除的上一个运算符号在第几位 
int no4(string,string);//寻找加减乘除的下一个运算符号在第几位 
int main(){
    string str;
    getline(cin,str);
    str = no1(str);
    int s = str.length();
    int s1 = str.find("+");
    int s2 = str.find("-");
    int s3 = str.find("*");
    int s4 = str.find("/");
    while((s1>0 && s1<s) || (s2>0 && s2<s) || (s3>0 && s3<s) || (s4>0 && s4<s)){
        if(s1>0 && s1<s && (s1<s2 || s1>s2 && s2<0) && (s3>s || s3<0) && (s4>s || s4<0)){
            str = str.replace(0,str.find("+",s1+1),to_string(no2(str,"+")));
            //cout<<s1<<endl;
            cout<<str<<endl;
        }else if(s2>0 && s2<s && (s3>s || s3<0) && (s4>s || s4<0)){
            str = str.replace(0,str.find("-",s2+1) || str.find("+",s2+1),to_string(no2(str,"-")));
            //cout<<s2<<endl;
            cout<<str<<endl; 
        }else if(s3>0 && s3<s && (s3<s4 || s3>s4 && s4<0)){
            str = str.replace(no3(str,"*")+1,no4(str,"*")-2,to_string(no2(str,"*")));
            //cout<<s3<<endl;
            cout<<str<<endl; 
        }else if(s4>0 && s4<s){
            str = str.replace(no3(str,"/")+1,no4(str,"/")-2,to_string(no2(str,"/")));
            //cout<<s4<<endl;
            cout<<str<<endl;
        }
        s = str.length();
        s1 = str.find("+");
        s2 = str.find("-");
        s3 = str.find("*");
        s4 = str.find("/");
    }
    return 0;
}
string no1(string str){
    while(str.find(" ")>=0 && str.find(" ")<=str.length()){
        str.replace(str.find(" "),1,"");
    }
    return str;
}
int no2(string c,string x){
    int a = stoi(c.substr(0,c.find(x)));
    int b = stoi(c.substr(c.find(x)+1));
    if(x=="+"){
        return a+b;
    }else if(x=="-"){
        return a-b;
    }else if(x=="*"){
        a = stoi(c.substr(no3(c,x)+1,c.find(x)));
        return a*b;
    }else if(x=="/"){
        a = stoi(c.substr(no3(c,x)+1,c.find(x)));
        return a/b;
    }
}
int no3(string c,string x){
    int i = c.find(x);
    while(c[i]!='+' && c[i]!='-'){
        i--;
    }
    return i;
}
int no4(string c,string x){
    int s_ = c.size();
    int s_1 = c.find("+",c.find(x)+1);
    int s_2 = c.find("-",c.find(x)+1);
    int s_3 = c.find("*",c.find(x)+1);
    int s_4 = c.find("/",c.find(x)+1);
    if(s_1>0 && s_1<s_ && (s_1<s_2 || s_1>s_2 && s_2<0) && (s_3>s_ || s_3<0) && (s_4>s_ || s_4<0)){
        return s_1;
    }else if(s_2>0 && s_2<s_ && (s_3>s_ || s_3<0) && (s_4>s_ || s_4<0)){
        return s_2;
    }else if(s_3>0 && s_3<s_ && (s_3<s_4 || s_3>s_4 && s_4<0)){
        return s_3;
    }else if(s_4>0 && s_4<s_){
        return s_4;
    }else{
        return s_;
    }
}

 

#include <bits/stdc++.h>
using namespace std;
string no1(string);//清除多余空格 
int no2(string,string);//计算
int no3(string,string);//寻找乘除的上一个运算符号在第几位 
int no4(string,string);//寻找加减乘除的下一个运算符号在第几位 
int main(){
    string str;
    getline(cin,str);
    str = no1(str);
    int s = str.length();
    int s1 = str.find("+");
    int s2 = str.find("-");
    int s3 = str.find("*");
    int s4 = str.find("/");
    while((s1>0 && s1<s) || (s2>0 && s2<s) || (s3>0 && s3<s) || (s4>0 && s4<s)){
        if(s1>0 && s1<s &&   (s1<s2 || s1>s2 && s2<0) && (s3>s || s3<0) && (s4>s || s4<0)){
            str = str.replace(0,no4(str,"+")-no3(str,"+")-1,to_string(no2(str,"+")));
            //cout<<s1<<endl;
            cout<<str<<endl;
        }else if(s2>0 && s2<s && (s3>s || s3<0) && (s4>s || s4<0)){
            str = str.replace(0,no4(str,"-")-no3(str,"-")-1,to_string(no2(str,"-")));
            //cout<<s2<<endl;
            cout<<str<<endl; 
        }else if(s3>0 && s3<s && (s3<s4 || s3>s4 && s4<0)){
            str = str.replace(no3(str,"*")+1,no4(str,"*")-no3(str,"*")-1,to_string(no2(str,"*")));
            //cout<<s3<<endl;
            cout<<str<<endl; 
        }else if(s4>0 && s4<s){
            str = str.replace(no3(str,"/")+1,no4(str,"/")-no3(str,"/")-1,to_string(no2(str,"/")));
            //cout<<s4<<endl;
            cout<<str<<endl;
        }
        s = str.length();
        s1 = str.find("+");
        s2 = str.find("-");
        s3 = str.find("*");
        s4 = str.find("/");
    }
    return 0;
}
string no1(string str){
    while(str.find(" ")>=0 && str.find(" ")<=str.length()){
        str.replace(str.find(" "),1,"");
    }
    return str;
}
int no2(string c,string x){
    int a = stoi(c.substr(0,c.find(x)));
    int b = stoi(c.substr(c.find(x)+1));
    if(x=="+"){
        return a+b;
    }else if(x=="-"){
        return a-b;
    }else if(x=="*"){
        a = stoi(c.substr(no3(c,x)+1,c.find(x)));
        return a*b;
    }else if(x=="/"){
        a = stoi(c.substr(no3(c,x)+1,c.find(x)));
        return a/b;
    }
}
int no3(string c,string x){
    int i = c.find(x)-1;
    while(c[i]!='+' && c[i]!='-'){
        i--;
        if(i<0){
            return 0;
        }
    }
    return i;
}
int no4(string c,string x){
    int s_ = c.size();
    int s_1 = c.find("+",c.find(x)+1);
    int s_2 = c.find("-",c.find(x)+1);
    int s_3 = c.find("*",c.find(x)+1);
    int s_4 = c.find("/",c.find(x)+1);
    if(s_1>0 && s_1<s_ && (s_1<s_2 || s_1>s_2 && s_2<0) && (s_3>s_ || s_3<0) && (s_4>s_ || s_4<0)){
        //cout<<1<<endl;
        return s_1;
    }else if(s_2>0 && s_2<s_ && (s_3>s_ || s_3<0) && (s_4>s_ || s_4<0)){
        //cout<<2<<endl;
        return s_2;
    }else if(s_3>0 && s_3<s_ && (s_3<s_4 || s_3>s_4 && s_4<0)){
        //cout<<3<<endl;
        return s_3;
    }else if(s_4>0 && s_4<s_){
        //cout<<4<<endl;
        return s_4;
    }else{
        //cout<<5<<endl;
        return s_;
    }
}