Probably one of the simplest skeletons I've got:

Code:
#include <windows.h>
#include <stdio.h>

int main(){

  HANDLE hProcess = 0;

  HWND hWindow;
  DWORD pid = 0;

  hWindow = FindWindow(NULL, "Window Name");
  if (hWindow){
     GetWindowThreadProcessId(hWindow, &pid);
  }

  hProcess = OpenProcess(PROCESS_ALL_ACCESS, 0, pid);

  if(hProcess != NULL)
     printf("Process Found!");
  else {
     printf("Process Not Found!");
     return 0;
  }
 
  //Writes byte values to 0x00567...
  BYTE valueToWrite[] ={0x90, 0x90};
  WriteProcessMemory(hProcess, (void*)0x00567A8F, (void*)&valueToWrite, sizeof(valueToWrite), NULL);

  return 0;
}
Its really handy if you want to make your own trainer. You of course need to know how to use it