Lpc2000

Hi:
I 'm working with Keil and GNU Compiler, and I try to use the printf 
function. I initialised the UART0 and the putchar function works 
fine. But the printf doesn't work. It only works if I use it as printf
("H"), but if I use printf("Hello"), it doesn't work.

This is the putchar function...

int putchar(int ch)  {                  /* Write character to Serial 
Port    */

  if (ch == '\n')  {
    while (!(U0LSR & 0x20));
    U0THR = CR;                      /* output CR */
  }
  while (!(U0LSR & 0x20));
  return (U0THR = ch);
}
I also include the stdio.h library. Do I have to include something 
else to have the printf function working correctly?

Thanks