string to char array

I am trying to make a command interpreter for a mud that i am working
on the problem i am having right now is that i cannot convert the
string into a char array.

This is the error I am getting now:

In file included from src/mud.cpp:3:
src/command.h: In static member function `static void
command::getCommand(std::string)':
src/command.h:38: error: incompatible types in assignment of `const
char*' to `char[256]'

the third line is just an include statement for command.h

this is the code for command.h

#ifndef COMMAND_H
#define COMMAND_H

#include <iostream>
#include <string>
#include <vector>
#include <cstring>

using namespace std;

class command {
    public:
    static void tokenizer(string str, vector<string>& words, string
delimiter);
    static void getCommand(string c);
    private:
    static vector<string> cmd;
};
vector<string> command::cmd;
void command::tokenizer(string str, vector<string>& words, string
delimiter){
    string::size_type pos1 = 0;
    string::size_type pos2 = str.find_first_of(delimiter);
    words.push_back(str.substr(pos1 ,pos2 - pos1));
    pos1 = pos2 + 1;
    while(pos2 <= str.length()){
        pos2 = str.find_first_of(delimiter, pos1);
        if(pos2 > str.length()){
            pos2 = str.length();
        }
        words.push_back(str.substr(pos1 ,pos2 - pos1));
        pos1 = pos2 + 1;
        pos2 += 1;
    }
}
void command::getCommand(string c){
    tokenizer(c, cmd, " ");
    if(cmd.size() == 1){
                  char oneWord[256];
                  oneWord = cmd[0].c_str();
                  for(int i = 0; oneWord.length; i++){
                          oneWord[i].toLower();
                  }
                  cmd[0] = oneWord;
                  // Move North
                  if(cmd[0] = "n" || cmd[0] = "north"){
                  }
                  // Move South
                  if(cmd[0] = "s" || cmd[0] = "south"){
                  }
                  // Move East
                  if(cmd[0] = "e" || cmd[0] = "east"){
                  }
                  // Move West
                  if(cmd[0] = "w" || cmd[0] = "west"){
                  }
                  // Move Up
                  if(cmd[0] = "u" || cmd[0] = "up"){
                  }
                  // Move Down
                  if(cmd[0] = "d" || cmd[0] = "down"){
                  }

    } else if(cmd.size() == 2){
    } else {
        cout << "invalid command!\n";
    }
}

#endif