c++ assign a class member function a lambda function

I'm looking to boost the computation efficiency of my code by make an run-time assignment of a class member function to one of many functions conditional on other class members. I would like to use lambda function, but I need help with a compile-time error.

I've created a simple test example:

#include <iostream>
using namespace std;

void foo() { /* do some generic number operator */ };

struct Number {
  int n;
  void (*doIt)();  // must be able to operate on this->n

  Number(int i):n(i) {
    doIt = foo;  // test function pointer, this works fine
  };

  void makeFunc() {

      auto _odd  = [this]() { /* op specific to odd */ };
      auto _even = [this]() { /* op specific to even */ };

      // test the lambda functions, works fine
      if (n%2) _odd();   
      else _even();

      // this is the desire goal, but does NOT compile
      if (n%2) doIt = _odd;   
      else     doIt = _even;  
  };
};

int main() {
  int i;
  cin >> i;
  Number e(i);
  e.makeFunc();
  e.doIt();
};

Assigning the function doIt to a generic function foo (in the class constructor) works fine and the lambda functions, _odd and _even themselves, work fine. But I cannot figure out how to assign either of them to doIt. The compile-time error I get is

error: cannot convert ‘Number::makeFunc()::__lambda0’ to ‘void (*)()’ in assignment

if (n%2) doIt = _odd;

I'm at a loss. I'm just discovered lambda function, but most of the discussion seem to focus on for-each operators or callback functions. It is not clear to me, from those discussion, how to fix my problem. What ever the solution, the operator must have access this.