一个4*4矩阵按键行引脚是PB0,PB1,PB2,PB3.列引脚是PB4,PB5,PB6,PB7.要求按下对应的按钮给字母n赋上对应的值。只许用HAL库函数。

好的，根据您的需求，下面是实现的代码：

#include "main.h"
#include <stdio.h>

#define ROW_PIN_0 GPIO_PIN_0
#define ROW_PIN_1 GPIO_PIN_1
#define ROW_PIN_2 GPIO_PIN_2
#define ROW_PIN_3 GPIO_PIN_3

#define COL_PIN_0 GPIO_PIN_4
#define COL_PIN_1 GPIO_PIN_5
#define COL_PIN_2 GPIO_PIN_6
#define COL_PIN_3 GPIO_PIN_7

void SystemClock_Config(void);
static void MX_GPIO_Init(void);

int main(void)
{
  HAL_Init();
  SystemClock_Config();
  MX_GPIO_Init();
  
  while (1)
  {
    uint8_t key_value = 0;  //保存按键值的变量
    uint8_t key_state = 0;  //保存按键状态的变量
    
    //扫描矩阵键盘是否有按键按下
    for (uint8_t i = 0; i < 4; i++)
    {
      HAL_GPIO_WritePin(GPIOB, 1 << i, GPIO_PIN_RESET);  //将第i行拉低
      
      for (uint8_t j = 0; j < 4; j++)
      {
        key_state = HAL_GPIO_ReadPin(GPIOB, 1 << (j + 4));  //读取第j列的状态
        
        if (key_state == GPIO_PIN_RESET)  //如果第j列被按下
        {
          key_value = i * 4 + j + 1;  //计算按键值
          break;
        }
      }
      
      HAL_GPIO_WritePin(GPIOB, 1 << i, GPIO_PIN_SET);  //将第i行拉高
    }
    
    if (key_value != 0)  //如果有按键按下
    {
      printf("您按下了%d号按键\n", key_value);
    }
  }
}

void SystemClock_Config(void)
{
  RCC_OscInitTypeDef RCC_OscInitStruct = {0};
  RCC_ClkInitTypeDef RCC_ClkInitStruct = {0};

  /** Initializes the RCC Oscillators according to the specified parameters
  * in the RCC_OscInitTypeDef structure.
  */
  RCC_OscInitStruct.OscillatorType = RCC_OSCILLATORTYPE_HSI|RCC_OSCILLATORTYPE_HSE;
  RCC_OscInitStruct.HSEState = RCC_HSE_ON;
  RCC_OscInitStruct.HSIState = RCC_HSI_ON;
  RCC_OscInitStruct.PLL.PLLState = RCC_PLL_ON;
  RCC_OscInitStruct.PLL.PLLSource = RCC_PLLSOURCE_HSE;
  RCC_OscInitStruct.PLL.PLLM = 8;
  RCC_OscInitStruct.PLL.PLLN = 336;
  RCC_OscInitStruct.PLL.PLLP = RCC_PLLP_DIV2;
  RCC_OscInitStruct.PLL.PLLQ = 7;
  if (HAL_RCC_OscConfig(&RCC_OscInitStruct) != HAL_OK)
  {
    Error_Handler();
  }
  /** Initializes the CPU, AHB and APB buses clocks
  */
  RCC_ClkInitStruct.ClockType = RCC_CLOCKTYPE_HCLK|RCC_CLOCKTYPE_SYSCLK
                              |RCC_CLOCKTYPE_PCLK1|RCC_CLOCKTYPE_PCLK2;
  RCC_ClkInitStruct.SYSCLKSource = RCC_SYSCLKSOURCE_PLLCLK;
  RCC_ClkInitStruct.AHBCLKDivider = RCC_SYSCLK_DIV1;
  RCC_ClkInitStruct.APB1CLKDivider = RCC_HCLK_DIV4;
  RCC_ClkInitStruct.APB2CLKDivider = RCC_HCLK_DIV2;

  if (HAL_RCC_ClockConfig(&RCC_ClkInitStruct, FLASH_LATENCY_5) != HAL_OK)
  {
    Error_Handler();
  }
}

static void MX_GPIO_Init(void)
{
  GPIO_InitTypeDef GPIO_InitStruct = {0};

  /* GPIO Ports Clock Enable */
  __HAL_RCC_GPIOB_CLK_ENABLE();

  /*Configure GPIO pins : PB0 PB1 PB2 PB3 
                           PB4 PB5 PB6 PB7 */
  GPIO_InitStruct.Pin = ROW_PIN_0|ROW_PIN_1|ROW_PIN_2|ROW_PIN_3|COL_PIN_0|COL_PIN_1|COL_PIN_2|COL_PIN_3;
  GPIO_InitStruct.Mode = GPIO_MODE_INPUT;
  GPIO_InitStruct.Pull = GPIO_PULLUP;
  HAL_GPIO_Init(GPIOB, &GPIO_InitStruct);

  /*Configure GPIO pin Output Level */
  HAL_GPIO_WritePin(GPIOB, ROW_PIN_0|ROW_PIN_1|ROW_PIN_2|ROW_PIN_3, GPIO_PIN_SET);
}

在上面的代码中，我们使用了HAL库函数来初始化GPIO口，并且使用了HAL库函数来读取矩阵键盘的按键状态。同时，我们还使用了printf函数将按键值输出到终端。请注意在使用printf函数之前需要添加相应的头文件和初始化，具体可以参考您所使用的开发板相关的文档。