Eval function on C++

//eval function by A-Man a.k.a Mr-A
#include <string>
#include <stdlib.h>
#include <sstream>


class Eval{
    private:
        int temp1, temp3;
        std::string temp2;
    public:
        Eval(std::string);
        std::string DIVIDE(std::string);
        std::string MULTIPLY(std::string);
        std::string ADD(std::string);
        std::string SUBTRACT(std::string);
        std::string IntToStr(int);
        std::string operation;
};


Eval::Eval(std::string oper){
    operation=oper;
    while(operation.rfind("(")!=std::string::npos){
        temp1=operation.rfind("(");
        temp3=operation.find(")", temp1);
        temp2=operation.substr(temp1+1,temp3-temp1-1);

        temp2=DIVIDE(temp2);     //D
        temp2=MULTIPLY(temp2);   //M
        temp2=ADD(temp2);        //A
        temp2=SUBTRACT(temp2);   //S

        operation.replace(temp1, temp3-temp1+1, temp2);
    }
    operation=DIVIDE(operation);     //D
    operation=MULTIPLY(operation);   //M
    operation=ADD(operation);        //A
    operation=SUBTRACT(operation);   //S
}




std::string Eval::IntToStr( int n )
  {
  std::ostringstream result;
  result << n;
  return result.str();
  }

std::string Eval::DIVIDE(std::string asdf){
            std::string larg,rarg;
            std::string a=asdf;
        int ilarg, irarg;

    while (a.find("/")!=std::string::npos){
        int pluspos=a.find("/");
        int temposha=pluspos;

        while (pluspos!=0 && isdigit(a[temposha-1])){
            larg = a.substr(temposha-1, 1)+larg;
            if (temposha==0) break;
            temposha--;
        }
        ilarg=temposha;
        temposha=pluspos;
        while (pluspos!=0 && isdigit(a[temposha+1])){
            rarg += a.substr(temposha+1, 1);
            if (temposha==a.length()) break;
            temposha++;
        }
        irarg=temposha;
        temposha=a.length();

        a.replace(ilarg,irarg-ilarg+1, IntToStr((atoi(larg.c_str())/atoi(rarg.c_str()))));
        larg=""; rarg="";}
    return a;
}

std::string Eval::MULTIPLY(std::string asdf){
            std::string larg,rarg;
            std::string a=asdf;
        int ilarg, irarg;

    while (a.find("*")!=std::string::npos){
        int pluspos=a.find("*");
        int temposha=pluspos;

        while (pluspos!=0 && isdigit(a[temposha-1])){
            larg = a.substr(temposha-1, 1)+larg;
            if (temposha==0) break;
            temposha--;
        }
        ilarg=temposha;
        temposha=pluspos;
        while (pluspos!=0 && isdigit(a[temposha+1])){
            rarg += a.substr(temposha+1, 1);
            if (temposha==a.length()) break;
            temposha++;
        }
        irarg=temposha;
        temposha=a.length();

        a.replace(ilarg,irarg-ilarg+1, IntToStr((atoi(larg.c_str())*atoi(rarg.c_str()))));
        larg=""; rarg="";}
    return a;
}

std::string Eval::ADD(std::string asdf){
            std::string larg,rarg;
            std::string a=asdf;
        int ilarg, irarg;

    while (a.find("+")!=std::string::npos){
        int pluspos=a.find("+");
        int temposha=pluspos;

        while (pluspos!=0 && isdigit(a[temposha-1])){
            larg = a.substr(temposha-1, 1)+larg;
            if (temposha==0) break;
            temposha--;
        }
        ilarg=temposha;
        temposha=pluspos;
        while (pluspos!=0 && isdigit(a[temposha+1])){
            rarg += a.substr(temposha+1, 1);
            if (temposha==a.length()) break;
            temposha++;
        }
        irarg=temposha;
        temposha=a.length();

        a.replace(ilarg,irarg-ilarg+1, IntToStr((atoi(larg.c_str())+atoi(rarg.c_str()))));
        larg=""; rarg="";}
    return a;
}
std::string Eval::SUBTRACT(std::string asdf){
            std::string larg,rarg;
            std::string a=asdf;
        int ilarg, irarg;

    while (a.rfind("-")!=std::string::npos&&a.rfind("-")!=0){

        int pluspos;
        pluspos=a.find("-");
        if (a.find("-")==0)pluspos=a.find("-", 1);

        int temposha=pluspos;

        while (a.rfind("-")!=0 && (isdigit(a[temposha-1])||(a.substr(temposha-1,1)=="-"&&temposha==1))){
            larg = a.substr(temposha-1, 1)+larg;
            temposha--;
            if (temposha==0) break;
        }
        ilarg=temposha;
        temposha=pluspos;
        while (a.rfind("-")!=0 && (isdigit(a[temposha+1])||(a.substr(temposha+1,1)=="-"&&temposha==1))){
            rarg += a.substr(temposha+1, 1);
            temposha++;
            if (temposha==a.length()) break;
        }
        irarg=temposha;
        temposha=a.length();

        a.replace(ilarg,irarg-ilarg+1, IntToStr((atoi(larg.c_str())-atoi(rarg.c_str()))));
        larg=""; rarg="";}
    return a;
}


int Evaluate(std::string strvalue){
    Eval Calc(strvalue);
    return atoi(Calc.operation.c_str());
}
std::string stringify(int whatever){
    Eval Calc("0");
    return Calc.IntToStr(whatever);
}