ADC/AnalogWatchdog/main.c
/**
  * @brief  Configures the different system clocks.
  * @param  None
  * @retval None
  */
void RCC_Configuration(void)
{
#if defined (STM32F10X_LD_VL) || defined (STM32F10X_MD_VL) || defined (STM32F10X_HD_VL)
  /* ADCCLK = PCLK2/2 */
  RCC_ADCCLKConfig(RCC_PCLK2_Div2);
#else
  /* ADCCLK = PCLK2/4 */
  RCC_ADCCLKConfig(RCC_PCLK2_Div4);
#endif
/* Enable peripheral clocks --------------------------------------------------*/
  /* Enable ADC1 and GPIO_LED clock */
  RCC_APB2PeriphClockCmd(RCC_APB2Periph_ADC1, ENABLE); //只对ADC1进行时钟使能，
                                                                                                 //却未使能ADC12_IN14对应的端口GPIOC使能，有什么说法吗？
}

这个在配置GPIO的时候会有PC口的操作的，你可以看看整个工程。