用51单片机做个密码锁（LCD屏上显示），按键输入，限次5次，超过5次蜂鸣器响的c语言代码

### 回答1：
这里是一份简单的51单片机密码锁的C语言代码的例子：

#include <reg51.h>
#include <LCD.h>

#define password "1234"
#define MAX_TRY 5

unsigned char i, j, flag, count, password_input[5];

void delay(unsigned int t)
{
    while (t--);
}

void buzzer()
{
    P1 = 0x01;
    delay(20000);
    P1 = 0x00;
    delay(20000);
}

void main()
{
    LCD_Init();
    count = MAX_TRY;
    while (1)
    {
        LCD_Clear();
        LCD_WriteString("Password Lock");
        LCD_WriteString("Enter password:");
        for (i = 0; i < 4; i++)
        {
            password_input[i] = getkey();
            LCD_WriteData(password_input[i]);
            delay(50000);
        }
        password_input[i] = '\0';
        flag = 1;
        for (j = 0; j < 4; j++)
        {
            if (password_input[j] != password[j])
            {
                flag = 0;
                break;
            }
        }
        if (flag)
        {
            LCD_Clear();
            LCD_WriteString("Access granted");
            delay(50000);
            break;
        }
        else
        {
            count--;
            LCD_Clear();
            LCD_WriteString("Access denied");
            LCD_WriteString("Remaining tries:");
            LCD_WriteData(count + '0');
            delay(50000);
            if (count == 0)
            {
                buzzer();
                break;
            }
        }
    }
}

注意：代码中使用了LCD驱动库，需要自行实现`LCD_Init()`、`LCD_Clear()`、`LCD_WriteString()`、`LCD_WriteData()`等函数。代码中使用了按键驱动库，需要自行实现`getkey()`函数。此代码仅作为参考，请根据您实际的硬件环境和需求进行修改。

### 回答2：
下面是一个使用51单片机搭建密码锁的C语言代码，通过LCD屏幕显示并限制了5次尝试的次数。超过5次的尝试将会触发蜂鸣器发出警报。

#include <reg51.h>
#include <stdio.h>

#define MAX_ATTEMPTS 5

sbit buzz = P1^0;
sbit rs = P2^0;           //LCD1602模块的接口输入端RS
sbit rw = P2^1;           //LCD1602模块的接口输入端RW
sbit en = P2^2;           //LCD1602模块的接口输入端E
#define LCD_data P0      //LCD1602的数据端口

void LCD_Init();
void LCD_Command(unsigned char cm);
void LCD_Show(unsigned char dat);
void LCD_String(unsigned char *s);

void delay(int n)
{
    int i, j;
    for(i=0;i<n;i++)
        for(j=0;j<120;j++);
}

void main()
{
    unsigned char password[6] = "12345";         // 设置密码
    unsigned char input[6];                      // 存储输入的密码
    unsigned char attempts = 0;                  

    LCD_Init();
    while(1) {
        LCD_Command(0x01);                        // 清除LCD屏幕

        LCD_String("Enter Password:");
        LCD_Command(0xC0);                        // 设置光标位置到第二行

        for(int i=0; i<5; i++) {                   
            input[i] = LCD_ReadKey();             // 读取按键输入
            LCD_Show('*');                        // 显示星号代替按下的按键

            if(input[i] != password[i]) {         // 验证密码位是否正确
                attempts++;
                if(attempts >= MAX_ATTEMPTS) {     // 如果尝试次数超过最大次数，则发出警报
                    buzz = 1;
                    delay(5000);
                    buzz = 0;
                    while(1);                       // 进入死循环，锁定系统
                }
                LCD_Command(0x01);                   // 清除LCD屏幕
                LCD_String("Wrong Password");
                delay(2000);
                break;                              // 输入错误后跳出循环
            }
        }

        if(attempts < MAX_ATTEMPTS) {                // 如果输入次数没达到最大限制则通过
            LCD_Command(0x01);                        // 清除LCD屏幕
            LCD_String("Access Granted");
            delay(2000);
            break;                                   // 跳出循环，解锁系统
        }
    }

    while(1);
}

void LCD_Init()
{
    LCD_Command(0x38);                              // LCD16x2设置，8位数据，两行显示
    delay(5);
    LCD_Command(0x0C);                              // 开启显示，无光标
    delay(5);
    LCD_Command(0x06);                              // 光标右移，无显现移动
    delay(5);
    LCD_Command(0x01);                              // 清除LCD屏幕
    delay(5);
}

void LCD_Command(unsigned char cm)
{
    LCD_data = cm;                       // 将指令写入数据端口
    rs = 0;                              // RS=0为指令
    rw = 0;                              // RW=0为写
    en = 1;                              // 使能E信号
    delay(5);
    en = 0;                              // 关闭E信号
}

void LCD_Show(unsigned char dat)
{
    LCD_data = dat;                      // 将数据写入数据端口
    rs = 1;                              // RS=1为显示字符
    rw = 0;                              // RW=0为写
    en = 1;                              // 使能E信号
    delay(5);
    en = 0;                              // 关闭E信号
}

void LCD_String(unsigned char *s)
{
    while(*s) {
        LCD_Show(*s);                    // 循环显示字符串
        s++;
    }
}

unsigned char LCD_ReadKey()
{
    unsigned char read_key = 0xFF;         // 设置初始值
    rs = 1;                                // RS=1为显示字符
    rw = 1;                                // RW=1为读
    en = 1;                                // 使能E信号
    delay(5);
    read_key = LCD_data;                   // 读取输入值
    en = 0;                                // 关闭E信号
    return read_key;
}

请注意，此代码仅提供了基本的密码验证和界面显示功能。你可以根据需求进一步优化和扩展代码。

### 回答3：
使用51单片机设计密码锁的C语言代码如下：

#include <reg51.h>

#define PASSWORD_LENGTH 4

sbit LCD_RS = P2^0;
sbit LCD_RW = P2^1;
sbit LCD_EN = P2^2;
sbit LCD_D4 = P2^4;
sbit LCD_D5 = P2^5;
sbit LCD_D6 = P2^6;
sbit LCD_D7 = P2^7;

sbit BUZZ = P3^0;

unsigned char password[PASSWORD_LENGTH] = "1234";  // 设置密码为"1234"
unsigned char input[PASSWORD_LENGTH];

void LCD_Init();
void LCD_Command(unsigned char command);
void LCD_WriteChar(unsigned char c);
void LCD_WriteString(unsigned char *string);
void LCD_Clear();
void Delay(unsigned int time);
int ValidatePassword(unsigned char *input, unsigned char *password);

void main() {
    unsigned char i;
    unsigned char attempt = 0;
    
    LCD_Clear();
    LCD_Init();
    LCD_WriteString("Enter password:");
    
    while (1) {
        for (i = 0; i < PASSWORD_LENGTH; i++) {
            while (!P1);
            input[i] = P1;
            Delay(100);
            P1 = 0xFF;
            
            LCD_WriteChar('*');
        }
        
        if (ValidatePassword(input, password)) {
            LCD_Clear();
            LCD_WriteString("Access granted!");
            break;
        } else {
            attempt++;
            if (attempt >= 5) {
                BUZZ = 1;  // 蜂鸣器响
                LCD_Clear();
                LCD_WriteString("Access denied!");
                break;
            }
            
            LCD_Clear();
            LCD_WriteString("Wrong password.");
            Delay(1000);
            LCD_Clear();
            LCD_WriteString("Enter password:");
        }
    }
    
    while (1);  // 无限循环，防止程序退出
}

int ValidatePassword(unsigned char *input, unsigned char *password) {
    unsigned char i;
    for (i = 0; i < PASSWORD_LENGTH; i++) {
        if (input[i] != password[i]) {
            return 0;
        }
    }
    return 1;
}

void LCD_Init() {
    LCD_Command(0x33);
    LCD_Command(0x32);
    LCD_Command(0x28);
    LCD_Command(0x0C);
    LCD_Command(0x01);
    Delay(1);
}

void LCD_Command(unsigned char command) {
    LCD_RS = 0;
    LCD_RW = 0;
    LCD_EN = 1;
    LCD_D4 = command >> 4;
    LCD_D5 = command >> 5;
    LCD_D6 = command >> 6;
    LCD_D7 = command >> 7;
    Delay(1);
    LCD_EN = 0;
    Delay(1);
    LCD_D4 = command >> 0;
    LCD_D5 = command >> 1;
    LCD_D6 = command >> 2;
    LCD_D7 = command >> 3;
    Delay(1);
    LCD_EN = 1;
    Delay(1);
    LCD_EN = 0;
    Delay(1);
}

void LCD_WriteChar(unsigned char c) {
    LCD_RS = 1;
    LCD_RW = 0;
    LCD_EN = 1;
    LCD_D4 = c >> 4;
    LCD_D5 = c >> 5;
    LCD_D6 = c >> 6;
    LCD_D7 = c >> 7;
    Delay(1);
    LCD_EN = 0;
    Delay(1);
    LCD_D4 = c >> 0;
    LCD_D5 = c >> 1;
    LCD_D6 = c >> 2;
    LCD_D7 = c >> 3;
    Delay(1);
    LCD_EN = 1;
    Delay(1);
    LCD_EN = 0;
    Delay(1);
}

void LCD_WriteString(unsigned char *string) {
    while(*string) {
        LCD_WriteChar(*string++);
    }
}

void LCD_Clear() {
    LCD_Command(0x01);
    Delay(1);
}

void Delay(unsigned int time) {
    unsigned int i, j;
    for(i = 0; i < time; i++)
        for(j = 0; j < 125; j++);
}

这段代码利用51单片机控制LCD显示屏和蜂鸣器，通过按键输入实现密码输入功能。程序中，首先初始化LCD显示屏后，设定一个4位数的密码（设定为"1234"），然后进入密码输入的循环中。在循环中，通过按键输入获取用户的输入，然后逐位比对输入密码和设定密码，如果匹配则显示"Access granted!"，否则累积输入次数，超过5次后蜂鸣器响，并显示"Access denied!"。如果密码正确或错误次数超过5次，则程序退出，进入无限循环。