Keep the console open long enough to see your program's output

#ifdef __cplusplus__
  #include <cstdlib>
#else
  #include <stdlib.h>
#endif

system("PAUSE");

#include <iostream>
#include <limits>

void PressEnterToContinue()
  {
  std::cout << "Press ENTER to continue... " << flush;
  std::cin.ignore( std::numeric_limits <std::streamsize> ::max(), '\n' );
  }

#include <stdio.h>

void PressEnterToContinue()
  {
  int c;
  printf( "Press ENTER to continue... " );
  fflush( stdout );
  do c = getchar(); while ((c != '\n') && (c != EOF));
  }

#include <stdio.h>

int main()
  {
  puts( "Hello world!" );
  PressEnterToContinue();
  return 0;
  }

#include <curses.h>

int main()
  {
  initscr();

  addstr( "Hello world!\n\n" );

  addstr( "\nPress a key to continue..." );
  cbreak();    /* turn off line-buffering */
  noecho();    /* turn off character echo */

  getch();     /* read and discard a single character (caveats!) */

  echo();      /* turn echo back on */
  nocbreak();  /* turn line-buffering back on */

  endwin();
  return 0;
  }

#include <conio.h>
#include <stdio.h>

void PressAKeyToContinue()
  {
  int c;
  printf( "\nPress a key to continue..." );
  c = getch();
  if (c == 0 || c == 224) getch();
  }

int main()
  {
  puts( "Hello world!" );
  PressAKeyToContinue();
  return 0;
  }

/* ---------------------------------------------------------------------------
 * PressAnyKey()
 * ---------------------------------------------------------------------------
 * Copyright 2008 Michael Thomas Greer
 * <a href="http://www.boost.org/LICENSE_1_0.txt">http://www.boost.org/LICENSE_1_0.txt</a>
 *
 * function
 *   Optionally print a message and and wait for the user to press (and
 *   release) a single key.
 *
 * arguments
 *   The message to print. If NULL, uses a default message. Specify the empty
 *   string "" to not print anything.
 *
 * returns
 *   The virtual keycode for the key that was pressed.
 *
 *   Windows #defines virtual keycode values like
 *     VK_UP
 *     VK_DOWN
 *     VK_RIGHT
 *     VK_LEFT
 *   which you can use to identify special keys.
 *
 *   Letter keys are simply the upper-case ASCII value for that letter.
 */
#include <windows.h>

int PressAnyKey( const char *prompt )
  {
  DWORD        mode;
  HANDLE       hstdin;
  INPUT_RECORD inrec;
  DWORD        count;
  char         default_prompt[] = "Press a key to continue...";

  /* Set the console mode to no-echo, raw input, */
  /* and no window or mouse events.              */
  hstdin = GetStdHandle( STD_INPUT_HANDLE );
  if (hstdin == INVALID_HANDLE_VALUE
  || !GetConsoleMode( hstdin, &mode )
  || !SetConsoleMode( hstdin, 0 ))
    return 0;

  if (!prompt) prompt = default_prompt;

  /* Instruct the user */
  WriteConsole(
    GetStdHandle( STD_OUTPUT_HANDLE ),
    prompt,
    lstrlen( prompt ),
    &count,
    NULL
    );

  FlushConsoleInputBuffer( hstdin );

  /* Get a single key RELEASE */
  do ReadConsoleInput( hstdin, &inrec, 1, &count );
  while ((inrec.EventType != KEY_EVENT) || inrec.Event.KeyEvent.bKeyDown);

  /* Restore the original console mode */
  SetConsoleMode( hstdin, mode );

  return inrec.Event.KeyEvent.wVirtualKeyCode;
  }

/* ---------------------------------------------------------------------------
 * PressAnyKey()
 * ---------------------------------------------------------------------------
 * Copyright 2008 Michael Thomas Greer
 * <a href="http://www.boost.org/LICENSE_1_0.txt">http://www.boost.org/LICENSE_1_0.txt</a>
 *
 * function
 *   Optionally print a message and and wait for the user to press (and
 *   release) a single key.
 *
 * arguments
 *   The message to print. If NULL, uses a default message. Specify the empty
 *   string "" to not print anything.
 *
 * returns
 *   The keycode for the key that was pressed.
 *
 *   Extended key codes (like arrow keys) are properly handled, but their
 *   keycode is not understood; they are simply returned as the last code in
 *   the sequence, negated. For example, it is likely that the arrow keys are:
 *
 *     UP_ARROW    = -'A' = -65
 *     DOWN_ARROW  = -'B' = -66
 *     RIGHT_ARROW = -'C' = -67
 *     LEFT_ARROW  = -'D' = -68
 *
 *   Exactly identifying the values for these keys requires a foray into the
 *   terminfo database, which is a subject for later. For now we'll leave it
 *   at this.
 */
#include <stdio.h>
#include <unistd.h>
#include <termios.h>

int PressAnyKey( const char* prompt )
  {
  #define MAGIC_MAX_CHARS 18
  struct termios initial_settings;
  struct termios settings;
  unsigned char  keycodes[ MAGIC_MAX_CHARS ];
  int            count;

  tcgetattr( STDIN_FILENO, &initial_settings );
  settings = initial_settings;

  /* Set the console mode to no-echo, raw input. */
  /* The exact meaning of all this jazz will be discussed later. */
  settings.c_cc[ VTIME ] = 1;
  settings.c_cc[ VMIN  ] = MAGIC_MAX_CHARS;
  settings.c_iflag &= ~(IXOFF);
  settings.c_lflag &= ~(ECHO | ICANON);
  tcsetattr( STDIN_FILENO, TCSANOW, &settings );

  printf( "%s", prompt ? prompt : "Press a key to continue..." );
  count = read( stdin, (void*)keycodes, MAGIC_MAX_CHARS );

  tcsetattr( STDIN_FILENO, TCSANOW, &initial_settings );

  return (count == 1)
       ? keycodes[ 0 ]
       : -(int)(keycodes[ count -1 ]);
  }

#if defined(__cplusplus)
  #include <string>
  inline int PressAnyKey( const std::string& prompt = "Press a key to continue..." )
    {
    return PressAnyKey( prompt.c_str() );
    }
#endif