Hello guys i am a student doing electronics and comm. of 5th semester B.E. i have written a code that opens or closes a door using a password/key as a practice i would like some feed back from you guys so as to improve as this is the first program i have written on my own

#include"reg51.h"
//#include"8052.h"

#define key_0 '0'
#define key_1 '1'
#define key_2 '2'
#define key_3 '3'
#define key_4 '4'
#define key_5 '5'
#define key_6 '6'
#define key_7 '7'
#define key_8 '8'
#define key_9 '9'
#define key_A 'A'
#define key_B 'B'
#define key_C 'C'
#define key_D 'D'
#define key_E 'E'
#define key_F 'F'
#define special_q '?'

sfr lcd = 0x90;	   //0x90 is port 1 address
sfr hex = 0x80;	   //0x80 is port 0 address
sbit RS = P2^0;
sbit RW = P2^1;
sbit EN = P2^2;

sbit door_state = P2^3;		//let state of 1 mean door is closed and 

state of 0 mean door is open
sbit motor1=P2^6;
sbit motor2=P2^7;
sbit alarm_1=P2^4;

void delay_ms(unsigned char);
void lcd_init();
void lcd_line(bit);
void lcd_com(unsigned char);
void lcd_disp(unsigned char);
void lcd_disp1(unsigned char dat[],bit delay1);
unsigned char keypad();
unsigned char invalid(unsigned char,unsigned char);
unsigned char compare(unsigned char one[], unsigned char two[], bit);
void change_key();
void close();
void open();
void alarm();

unsigned char  present_key[]= "12345600",wrong_count=0,right_count=0;
code unsigned char zero2nine[]= {"0 to 9 only"},wrong[]= {"wrong key.."}, 

lock_error[]= {"Lock error"};

code unsigned char key_state[]=        {0xEE , 0xED , 0xEB , 0xE7,
                                        0xDE , 0xDD , 0xDB , 0xD7,
                                        0xBE , 0xBD , 0xBB , 0xB7,
                                        0x7E , 0x7D , 0x7B , 0x77
                                       };

code unsigned char digit[]=        { key_0 , key_4 , key_8  , key_C ,
                                     key_1 , key_5 , key_9  , key_D ,
                                     key_2 , key_6 , key_A  , key_E ,
                                     key_3 , key_7 , key_B  , key_F
                                   };
// main program starts here
void main()
{
    unsigned char i,j,temp,password[8]=0;
    code unsigned char right[]= {"right"},p_wd[]= {"Key:"};
    code unsigned char  lcd_open[]= {"open..."}, lcd_close[]= 

{"close..."};
    unsigned char flag_g=0;//,a;
    code unsigned char lcd_door[]= {"A-> open/close"};
    code unsigned char lcd_change[]= {"B-> Change key"}, lcd_exit[]= {"E-> 

Exit"};
//begin:
    while(1)
    {
        lcd_init();
        lcd_disp1(p_wd,0);
        lcd_line(1);

        //This is where password is taken as input

        for(i=0; i<8; i++)
        {
            password[i]=keypad();					  

// reading from keypad

            flag_g=invalid(password[i],i);

            if(flag_g==0xaa || flag_g==0xff || flag_g==0xDD)
            {
                break;
            }
            lcd_disp( special_q );	 // 0x3f is hex value of ascii 

character "?" (question mark)
        }

        if(flag_g==0xff || flag_g==0xDD)
        {
            flag_g=0;
            continue;
        }
        flag_g=0;
        right_count=0;
        //comparing is done here
        flag_g = compare(password,present_key,1);
        if(flag_g==0xff)
        {
            flag_g=0;
            continue;
        }
        if(right_count==7)
        {
            wrong_count=0;
            lcd_disp1(right,1);
        }

    // The menu is shown here
        j=0;
        while(j<=100)
        {
            j++;
            for(i=0; i<1; i++)
            {
                lcd_disp1(lcd_door,0);
                temp=keypad();
                if(temp != 0xff)  break;

                lcd_disp1(lcd_change,0);
                temp=keypad();
                if(temp != 0xff)  break;

                lcd_disp1(lcd_exit,0);
                temp=keypad();
                if(temp != 0xff)  break;
            }

            if(temp==key_C)
            {
                if(door_state==1)
                {
                    lcd_disp1(lcd_open,0);
                    open();
                }
                else
                {
                    lcd_disp1(lcd_close,0);
                    close();
                }
            }

            else if(temp==key_D)
            {
                change_key();
            }

            else if(temp==key_B)
            {
                temp=0;
                flag_g=0xff;
                break;
            }
        }
        continue;
        /*if(flag_g==0xff)
        {
            flag_g=0;
            continue;
        }*/
        //sleep();
    }
}

/*
   Purpose: This function is used to create delay between operations with 

a minimum of 1 ms and maximum
            of about 256 ms of delay
   Input: input is 8 bit i.e. unsigned char. The input specifieds the 

amount of delay called
*/

void delay_ms(unsigned char u)
{
    unsigned char i;
    unsigned int j;
    //
    for(i=0; i<u; i++)
    {
        for(j=0; j<1275; j++);
    }
}

/*
        Purpose: This function is used to pass on commands to the LCD 

display connected to port P1.
        Input: input is 8 bit i.e. unsigned char. The input specifieds 

command to be given to the LCD.
*/

void lcd_com(unsigned char x)
{
    RS=0;							 //command 

mode
    RW=0;
    EN=1;

    lcd=x;
    delay_ms(5);
    EN=0;
    delay_ms(5);
}
/*
        Purpose: This function initialises the LCD screen
*/
void lcd_init()
{
    lcd_com(0x0E);
    lcd_com(0x38);
    lcd_com(0x06);
}
/*
        Purpose: This function is used to change/define the line which is 

to be used in the LCD.
        Input: input is 1 bit.
               The input of '0' makes the cursor to go to the line 0
               and input of '1' makes the cursor to go to line 1.
*/

void lcd_line(bit line)
{
    if(line==0)
        lcd_com(0x80);			        //line one
    else
        lcd_com(0xC0);			        //return home
}
/*
        Purpose: This function is used to pass on data to the LCD display 

connected to port P1.
        Input: Input is 8 bit i.e. unsigned char. The input specifieds 

data to be given to the LCD.
*/
void lcd_disp(unsigned char x)
{
    RS=1;
    RW=0;
    EN=1;

    lcd=x;
    delay_ms(5);
    EN=0;
    delay_ms(5);
    //lcd_com(0x06);
}


void lcd_disp1(unsigned char dat[], bit a)
{
    unsigned char i;
    lcd_com(0x01);
    lcd_line(0);

    for(i=0; i <sizeof(dat) ; i++)
    {
        if(i==8)
        {
            lcd_line(1);
        }
        lcd_disp(dat[i]);
    }
    // Four second delay is to be expected
    if(a==1)
    {
        delay_ms(255);         delay_ms(255);         delay_ms(255);       

   delay_ms(255);
        delay_ms(255);         delay_ms(255);	      delay_ms(255);       

   delay_ms(255);
        delay_ms(255);         delay_ms(255);		  delay_ms(255);   

       delay_ms(255);
        delay_ms(255);         delay_ms(255);         delay_ms(255);	   

   delay_ms(255);
        delay_ms(255);	       delay_ms(255);
    }
    else
    {
        delay_ms(255);	       delay_ms(255);
    }
}
/*
        Purpose: This function is used to get data from the keypad 

connected to port P0.
        Return: Return is 8 bit i.e. unsigned char. The Return is the 

value of the button pressed in the keypad.
*/
unsigned char keypad()
{
    unsigned char i,temp=0,temp1=0,temp2=0xff,wait=0,wait1=0;

    while(1)
    {
        //write program to prevent indefinite waiting here
        wait++;
        hex = 0x0f;
        delay_ms(10);

       // temp = hex;
       // temp &= 0x0f;

        for(i=0; i<4; i++)
        {
            if(i==0)        hex = temp1= 0xEF;
            else if(i==1)   hex = temp1 = 0xDF;
            else if(i==2)   hex = temp1 = 0xBF;
            else if(i==3)   hex = temp1 = 0x7F;

            temp = hex;
            temp &= 0x0f;
            temp1&= 0xf0;

            if(temp != 0x0F)
            {
                delay_ms(50);
                delay_ms(50);
                delay_ms(50);
                delay_ms(50);

                temp=hex;
                temp&=0x0F;
                if(temp!=0x0F)
                {
                    temp = temp | temp1;
                    delay_ms(50);
                    break;
                }
            }
        }
        for(i=0; i<16; i++)
        {
            if(key_state[i]==temp)
                temp2=digit[i];
        }

        if(wait==255)
        {
            wait=0;
            wait1++;
            if(wait1==255)
            {
                temp2=0xff;
                return temp2;
            }
        }
    }
    return temp2;
}
/*
        Purpose: This function should be used to close the lock of the 

door
*/
void close()
{
    unsigned char a=0;
    if(door_state==0)
    {
        motor1=0;
        motor2=1;
        while(a<=200)
        {
            a++;
            if(door_state==1)
            {
                return;
            }
            delay_ms(5);
        }
        lcd_com(0x01);
        lcd_line(0);

        lcd_disp1(lock_error,1);
        return;
    }
}
/*
        Purpose: This function should be used to open the lock of the door
*/
void open()
{
    unsigned char a=0;
    if(door_state==1)
    {
        motor1=0;
        motor2=1;
        while(a<=200)
        {
            a++;
            if(door_state==0)
            {
                return;
            }
            delay_ms(5);
        }
        lcd_com(0x01);
        lcd_line(0);

        lcd_disp1(lock_error,1);
        return;
    }
}
/*
  Purpose: This function checks for illegal buttons pressed and gives 

appropriate return
  Input: (x,i) : x is the input from the keypad and i is the index of the 

key presed
  Return: (flag) :return value of 0xaa is given if 14 or enter is pressed
                  0xDD is returned if no key is pressed
                  and 0xff is given if 15 or escape is pressed
*/
unsigned char invalid(unsigned char x,unsigned char i)
{
    unsigned char flag,temp;//,j;
    while(i==7)
    {
        temp=keypad();

        if(temp==key_A)        //14 is return/enter, key 15 is escape
        {
            flag=0xaa;
            break;
        }
        else if(temp==key_B || temp== 0xff)
        {
            flag=0xff;
            break;
        }
    }

    if(x==key_A)
    {
        flag=0xaa;
    }
		/*
       		Do not accept the values of 10,11,12,13. Password must 

contain only 0 to 9 only
		*/
    else if(x==key_C || x==key_D || x==key_E || x==key_F)
    {
        flag=0xDD;

        lcd_disp1(zero2nine,1);

    }
    else if(x==key_B || x==0xff)
    {
        flag=0xff;
    }
    return flag;
}
/*
        Purpose: this is used to compare the 2 variables and give 

corresponfing output
*/
unsigned char compare(unsigned char one[],unsigned char two[], bit a)
{
    unsigned char flag_c,i;
    code unsigned char mismatch[]= {"Key mismatch"},try_again[]= {"Try 

again"};;
    flag_c=0x00;
    right_count=0;
    for(i=0; i<8; i++)
    {
        if(one==two)
        {
            right_count++;
        }
        else
        {
            wrong_count++;
            right_count=0;
            flag_c=0xff;
            break;
        }
    }
    if(flag_c==0xff)
    {
        if(a==1)
        {
            lcd_disp1(wrong,1);
            if(wrong_count>=5)
            {
                alarm();
                return 0xff;
            }
        }
        else if(a==0)
        {
            lcd_disp1(mismatch,0);
            delay_ms(200);
            lcd_disp1(try_again,0);
            return 0xff;
        }
    }
    return flag_c;
}
/*
        Purpose: 1. This function is used to get data from the keypad 

connected to port P0 twice.
                 2. Then compare them and then change the password.
*/
void change_key()
{

    unsigned char i,flag_g, temp, password[8]=0, pass_confirm[8]=0;// j, 

count;
    code unsigned char new_key[]= {"New key:"},confirm[]= {"Confirm:"};
    code unsigned char key_changed[]= {"key changed..."};

    while(1)
    {
        lcd_disp1(new_key,0);
        lcd_line(1);
        temp=0;

        /*   take new password    */
        for(i=0; i<8; i++)
        {
           // count++;
            password[i]=keypad();

            flag_g=invalid(password[i],i);
            if(flag_g==0xaa || flag_g==0xDD)
            {
                break;
            }
            else if(flag_g==0xff)
            {
                return;
            }
            lcd_disp( special_q );	 	// 0x3f is hex value of 

ascii character "?"
        }

        if(flag_g==0xDD)
        {
            flag_g=0;
            continue;
        }
        flag_g=0;
        //confirmation is done here

        lcd_disp1(confirm,0);
        lcd_line(1);

        /*  take new password   */
        for(i=0; i<8; i++)
        {
            pass_confirm[i]=keypad();

            flag_g=invalid(pass_confirm[i],i);
            if(flag_g==0xaa || flag_g==0xDD)
            {
                break;
            }
            else if(flag_g==0xff)
            {
                return;
            }
           // count++;
            lcd_disp( special_q );	 // 0x3f is hex value of ascii 

character "?"
        }
        if(flag_g==0xDD)
        {
            flag_g=0;
            continue;
        }
        flag_g=0;

        flag_g=compare(password,pass_confirm,0);
        if(flag_g==0xff)
        {
            flag_g=0;
            continue;
        }
        flag_g=0;

        if(right_count==7)
        {
            for(i=0; i<8; i++)
            {
                present_key[i] = password[i];
            }
            lcd_disp1(key_changed,1);
            right_count=0;
        }
    }
    return;
}
/*
    Purpose:This function calls alarm and switches off the LCD display 

until a 5 digit master password is pressed
*/
void alarm()
{
    code unsigned char crack[]= "0F3C7";
    unsigned char temp[5],a,b,count;
    /*   Program to switch off lcd display here    */
    lcd_com(0x08);
    alarm_1=1;

    while(1)
    {
        for (a=0; a<5; a++)
        {
            temp[4]=keypad();
        }
        count=0;
        for (a=0 ; a<5 ; a++)
        {
            if(temp[a] != crack[a])
            {
                alarm_1=1;
                for (b=0; b<5; b++)
                {
                    temp[a]=0;
                }
                break;
            }
            else if(temp[a]==crack[a])
            {
                count++;
            }
        }
        if(count!=4)
        {
            continue;
        }
        else
        {
            delay_ms(200);
            alarm_1=0;
            return;
        }
    }
}