#include<stdlib.h>
#include<string.h>

volatile char *col_pinC=0x28; // Pointer to access rows of the keypad (Port C)
volatile char *rows_pinA=0x22; // Pointer to access columns of the keypad (Port A)

void delay()   //delay function to waste time
{
  volatile long i;
  for(i=0;i<50000;i++);
}

void outdata(volatile char out)  // sending data to lcd
{
    volatile char *outputport_f;
    outputport_f=0x31; //f port (d0-d7)
    *outputport_f=out; //sending data on port f
}

void outcontrol(volatile char control)//to control command or data and enable
{
    volatile char *outputport_k;
    outputport_k=0x108;// k port (0-pin RS and 1-Enable )
    *outputport_k=control; //send control data 
}

void LCD_CMD(volatile char c) //send cammand to lcd
{
  outdata(c); //writing on to pins
  outcontrol(0x02); //RS=0,E=1
  delay();
  outcontrol(0x00); //RS=0,E=0
  delay();
}

void init_lcd(void)//initialing lcd
{
     LCD_CMD(0x38); //enable all pixels
     LCD_CMD(0X0E); //display on cursor blinking
     LCD_CMD(0X01); //Clear display screen
     LCD_CMD(0x80); //force cursor to beginning of 1st line
}

void init_LCD_pin() //configurate the pins of lcd
{
     volatile char *outputport_f,*outputport_k;
     outputport_f=0x30; outputport_k=0x107; 
     *outputport_f=0xFF; //f port as output
     *outputport_k=0x03; //k -1(RS) and 2(E) pin as output
}

void LCD_DATA(volatile char c)//to send character on lcd
{
    outdata(c); //writing on pins
    outcontrol(0x03);//RS=1,E=1
    delay();
    outcontrol(0x01);//RS=1,E=0
    delay();
}

void init_keypad_pin()//configurate the pins of keypad
{
  //making port C first four pins as ouput
    volatile char *col_dirC;
    col_dirC=0x27;
    *col_dirC=0x00;

  //making port A frist four as input
    volatile char *row_dirA;
    row_dirA=0x21;
    *row_dirA=0x0F;
}

volatile char keypad_scan()//scaning row and colums to know which key is pressed
{
   volatile long i;
   for(i=0;i<4;i++)
   {
    *rows_pinA=1<<i;//set one row at a time
    int a=*col_pinC;//reading colum values
    switch(i)
    {
      case 0:
       if(a==1) return '1';
       if(a==2) return '2';
       if(a==4) return '3';
       if(a==8) return '+';

       case 1:
       if(a==1) return '4';
       if(a==2) return '5';
       if(a==4) return '6';
       if(a==8) return '-';

       case 2:
       if(a==1) return '7';
       if(a==2) return '8';
       if(a==4) return '9';
       if(a==8) return '*';

       case 3:
       if(a==1) return 'c';
       if(a==2) return '0';
       if(a==4) return '=';
       if(a==8) return '/';
    }
   }
}

void setup() {
  // put your setup code here, to run once:
  volatile char a[10],b[10];
	volatile long i,j=0,k,num[10],result=0,c,temp,sign=1,l=0;
	volatile char op[10];

  init_keypad_pin(); //pin configuration for key pad
  init_LCD_pin();//pin configuration for LCD
  init_lcd();//intialing lcd
while(1)
{
  *rows_pinA=0x0F; //set all rows high
  *col_pinC=0x00;//set all rows low
     while(*col_pinC==0);//wait for key press
     delay();//debouncing delay
     while(*col_pinC==0);//to stabalize
     a[i]=keypad_scan();//get the pressed key
    if(a[i]=='c')// if pressed key is ac to clear everything
    {
    i=0;
    j=0;
    l=0;
    result=0;
    sign=1;
		strcpy(op,"");
		strcpy(a,"");
    strcpy(b,"");
  init_lcd();
    }
else{
    LCD_DATA(a[i]);//display the pressed key on lcd
		i++;
if((i==1)&&(j==0)&&(a[i-1]=='-')) //to check frist number is negative
{

    sign=-1;
    strcpy(a,"");
    i=0;	
  
}
 if((a[i-1]=='+')||(a[i-1]=='-')||(a[i-1]=='*')||(a[i-1]=='/')||(a[i-1]=='='))
{
    int k=0;
    num[j] = 0;
    while(a[k]>='0'&&a[k]<='9')//convert character to number
    {
			num[j]=num[j]*10+(a[k]-48);
      k++;
    }
   num[j]=num[j]*sign;//apply sign to number
   sign=1;
   if(a[i-1]!='=')
   {
			op[j]=a[i-1];
			strcpy(a,"");
       i=0;	
			j++;
   }
else
{
    result=num[0];
for(i=0;i<j;i++)
{
if(op[i]=='+')
{
	result=result+num[i+1];
}
else if(op[i]=='-')
{
	result=result-num[i+1];
}
else if(op[i]=='*')
{
	result=result*num[i+1];
}
else if(op[i]=='/')
{
	result=result/num[i+1];
}
}
k=0;
 temp=result;
  LCD_CMD(0x01);//clear lcd
  if(temp==0)//display 0 if result is zero
  {
    LCD_DATA('0');
  }
  if(temp<0)//display - sign if result is negative
{
  	LCD_DATA('-');
    temp=-temp;
}
while(temp)
		{
			c=temp%10;
			b[k]=c+48;//convert number to character
			temp=temp/10;
			k++;
		}
				for(j=k-1;j>=0;j--)
		{
			LCD_DATA(b[j]);		
		}
		i=0;
    j=0;
    l=0;
    num[j]=result;//store result to further calculation
    j++;
		strcpy(op,"");
		strcpy(a,"");
    strcpy(b,"");
		
	}
}
	}
}
}


void loop() {
  // put your main code here, to run repeatedly:

}