Pointer Trouble (GCC complains)

When trying to compile this:

Code:

#include <iostream>

using namespace std;

void DoubleIt(int *pointer);

int main ()
{
  int a = 0;
  int b = 0;
  
  //int *ptr_a = &a;
  //int *ptr_b = &b;
  
  cout << "Enter a value for a: ";
  cin >> a;
  
  cout << "Enter a value for b: ";
  cin >> b;
  
  cout << "Double a is " << DoubleIt(&a) << ".\n";
  cout << "Double b is " << DoubleIt(&b) << ".\n";
  
  return 0;
}

void DoubleIt(int *pointer)
{
  *pointer *= 2;
}

GCC says this:

Code:

$ g++ doubleit.cpp -o doubleit                                                      
doubleit.cpp: In function ‘int main()’:                                                                  
doubleit.cpp:22: error: no match for ‘operator<<’ in ‘std::operator<< [with _Traits = std::char_traits<char>](((std::basic_ostream<char, std::char_traits<char> >&)(& std::cout)), ((const char*)"Double a is ")) << DoubleIt(ptr_a)’

(and a WHOLE lot more (looks like mostly the same message though)).

This strikes me as strange, because it seems to be complaining about I/O, but as far as I can tell there aren't any syntax errors. I've been looking at this for about an hour and can't figure out what's wrong.

Any ideas?

DoubleIt returns void (doesn't return anything).

You are using its return values

Code:

  cout << "Double a is " << DoubleIt(&a) << ".\n";
  cout << "Double b is " << DoubleIt(&b) << ".\n";

.... Oh man... *FACEPALM* I think it's time for bed. lol. Thanks for the help.