Assignment in Const C++ functions -

i have assignment in have write simple class. class must hold array of strings, , contain overload of '+' operator, combines elements of 2 arrays new array , returns it.

additionally, function must 'const', ran problems. when trying change class "size" attribute , array holding, errors. error when trying return object. understand cause first 2 errors because have declared function 'const', question is, proper way reassign these values inside of const method?

don't tear me bad, i've begun learning c++, , concepts bit new me. i've tried researching subject, haven't found useful answers. being said, need function working, appreciated.

here class:

class firstclass{  private:     string* slist;     unsigned int _size;  public:     firstclass(const unsigned int initsize = 1);         // copy, assignment, , destructor      firstclass& operator+(const firstclass& add)const; };          firstclass::firstclass(const unsigned int initsize):_size(initsize) {     slist = new string[initsize];     return; }    firstclass& firstclass::operator+(const firstclass& add) const{     if(add.slist){         int prevsize = this->_size;         this->_size += add._size;   // can't         string newlist[this->_size];           for(int a=0; a<prevsize; a++){             newlist[a] = this->slist[a];         }         for(int b=0; b<add._size; b++){             slist[b+prevsize] = add.slist[b];         }         delete [] slist;         this->slist = newlist; // or     }      return *this; // or } 

edit: quick response, , clearing doing. here revised code.

firstclass firstclass::operator+(const firstclass& add) const{     firstclass ma(this->_size + add._size);      if(add.slist){          for(int a=0; a<this->_size; a++){             ma.slist[a] = this->slist[a];         }         for(int b=0; b<add._size; b++){             ma.slist[b+this->_size] = add.slist[b];         }     }      return ma; } 

an addition operator should return new object, not reference 1 of operands. doesn't make sense a+b modify a or b, or return reference 1 of them.

with in mind, easy see how operator can const.

firstclass operator+(const firstclass& rhs) const; 

you implement mutating operator+=, , implement operator+ in terms of that:

firstclass& operator+=(const firstclass& rhs);  firstclass operator+(const firstclass& rhs) const  {   firstclass ret = rhs;   ret += *this;   return ret; } 

or non-member:

firstclass operator+(const firstclass& lhs, const firstclass& rhs) {    firstclass ret = lhs;   ret += rhs;   return ret;  }