使用标准库，编写stm32f103c8t6通过USART2串口接收和输出数值的程序

好的，这里给你提供一个示例程序，使用USART2串口接收和输出数值：

#include "stm32f10x.h"
#include <stdio.h>
#include <string.h>

void USART2_Init(void)
{
    GPIO_InitTypeDef GPIO_InitStructure;
    USART_InitTypeDef USART_InitStructure;

    RCC_APB2PeriphClockCmd(RCC_APB2Periph_GPIOA | RCC_APB2Periph_AFIO, ENABLE);
    RCC_APB1PeriphClockCmd(RCC_APB1Periph_USART2, ENABLE);

    GPIO_InitStructure.GPIO_Pin = GPIO_Pin_2;
    GPIO_InitStructure.GPIO_Mode = GPIO_Mode_AF_PP;
    GPIO_InitStructure.GPIO_Speed = GPIO_Speed_50MHz;
    GPIO_Init(GPIOA, &GPIO_InitStructure);

    GPIO_InitStructure.GPIO_Pin = GPIO_Pin_3;
    GPIO_InitStructure.GPIO_Mode = GPIO_Mode_IN_FLOATING;
    GPIO_Init(GPIOA, &GPIO_InitStructure);

    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;
    USART_Init(USART2, &USART_InitStructure);

    USART_Cmd(USART2, ENABLE);
}

int main(void)
{
    USART2_Init();

    char buf[16];
    uint16_t value = 0;
    while (1)
    {
        if (USART_GetFlagStatus(USART2, USART_FLAG_RXNE) == SET)
        {
            char ch = USART_ReceiveData(USART2);
            if (ch >= '0' && ch <= '9')
            {
                value = value * 10 + (ch - '0');
            }
            else if (ch == '\r' || ch == '\n')
            {
                sprintf(buf, "Received: %d\r\n", value);
                int len = strlen(buf);
                for (int i = 0; i < len; i++)
                    USART_SendData(USART2, buf[i]);
                value = 0;
            }
        }
    }
}

这个程序使用USART2串口接收和输出数值，波特率为115200。当接收到数字串时，将其转换为整数并输出；当接收到回车或换行符时，输出接收到的数字。注意，本程序只是一个示例，实际应用中需要根据具体情况进行修改。