stm32串口实验的问题，求帮助

程序作用为从键盘输入字符到开发板，超级终端会收到相同字符
请问程序是如何执行的?红色部分什么意思?

#pragma import(__use_no_semihosting_swi)
#define PRINT_ON_LCD
USART_InitTypeDef USART_InitStructure;


#ifdef __GNUC__
  #define PUTCHAR_PROTOTYPE int __io_putchar(int ch)
#else
  #define PUTCHAR_PROTOTYPE int fputc(int ch, FILE *f)
#endif


#ifdef PRINT_ON_LCD
void Display_Init(void);
void Display(void);
#endif  


int main(void)
{
  
#ifdef PRINT_ON_LCD
  
  Display_Init();

  Display();
#endif
   
  
  USART_InitStructure.USART_BaudRate = 115200;
  USART_InitStructure.USART_WordLength = USART_WordLength_8b;
  USART_InitStructure.USART_StopBits = USART_StopBits_1;
  USART_InitStructure.USART_Parity = USART_Parity_No;
  USART_InitStructure.USART_HardwareFlowControl = USART_HardwareFlowControl_None;
  USART_InitStructure.USART_Mode = USART_Mode_Rx | USART_Mode_Tx;

  STM_EVAL_COMInit(COM1, &USART_InitStructure);


  printf("\n\rUSART Printf Example: retarget the C library printf function to the USART\n\r");

  while (1)
  {
  

找本C语言的书看看吧。

是定义一个函数或变量的语句啊