/*  Name     : main.c
 *  Purpose  : Source code for Keypad Interfacing with Arduino.
 *  Author   : Gemicates
 *  Date     : 18-01-2018
 *  Website  : www.gemicates.org
 *  Revision : None
 */
#include<LiquidCrystal.h>                   // this header file has instructions written in it, which enables
                                            // the user to interface an LCD to UNO in 4 bit mode without any fuzz

LiquidCrystal lcd(8, 9, 10, 11, 12, 13);    // sets the interfacing pins
int R1=0;                                   // declares R1, R2, R3, R4, C1, C2, C3, C4,
int R2=1;                                   // D4, D5, D6, D7 as integer type
int R3=2;
int R4=3;
int C1=4;
int C2=5;
int C3=6;
int C4=7;
int D4;
int D5;
int D6;
int D7;

void setup()
{
    pinMode(R1,OUTPUT);                     // initialize the digital pins R1, R2, R3, R4 as outputs
    pinMode(R2,OUTPUT);
    pinMode(R3,OUTPUT);
    pinMode(R4,OUTPUT);
    pinMode(C1,INPUT);                      // initialize the digital pins C1, C2, C3, C4 as inputs
    pinMode(C2,INPUT);
    pinMode(C3,INPUT);
    pinMode(C4,INPUT);
    digitalWrite(C1,HIGH);                  // Drive C1, C2, C3, C4 to HIGH
    digitalWrite(C2,HIGH);
    digitalWrite(C3,HIGH);
    digitalWrite(C4,HIGH);
    lcd.begin(16, 2);                       // initializes the 16*2 LCD
    lcd.setCursor(0,0);                     // sets the cursor at row 0 column 0
    lcd.print("16*2 LCD MODULE");           // prints 16*2 LCD MODULE
 }

void loop()
{
    lcd.setCursor(0,1);                     // sets the cursor at row 0 column 1
    digitalWrite(R1,LOW);                   // Drive R1 to LOW
    digitalWrite(R2,HIGH);                  // Drive R2, R3 ,R4 to HIGH
    digitalWrite(R3,HIGH);
    digitalWrite(R4,HIGH);
    D4=digitalRead(C1);                     // sets D4 equal to the input C1
    D5=digitalRead(C2);                     // sets D5 equal to the input C2
    D6=digitalRead(C3);                     // sets D6 equal to the input C3
    D7=digitalRead(C4);                     // sets D7 equal to the input C4
    
    if(D4==LOW)
    {
      lcd.print("7");                       // prints '7'
    }
    
   else
    {
      if(D5==LOW)
      {
        lcd.print("8");                     // prints '8'
      }
  
   else
   {
    if(D6==LOW)
    {
      lcd.print("9");                       // prints '9'
    }
  
   else
   {
   if(D7==LOW)
   {
    lcd.print("/");                         // prints '/'
   }
   }}}

   digitalWrite(R1,HIGH);                   // Drive R1 to HIGH
   digitalWrite(R2,LOW);                    // Drive R2 to LOW
   digitalWrite(R3,HIGH);                   // Drive R3, R4 to HIGH
   digitalWrite(R4,HIGH);
   D4=digitalRead(C1);                      // sets D4 equal to the input C1
   D5=digitalRead(C2);                      // sets D5 equal to the input C2
   D6=digitalRead(C3);                      // sets D6 equal to the input C3
   D7=digitalRead(C4);                      // sets D7 equal to the input C4
   
   if(D4==LOW)
   {
    lcd.print("4");                         // prints '4'
   }
  
   else
   {
    if(D5==LOW)
    {
      lcd.print("5");                       // prints '5'
    }
   
  else
  {
    if(D6==LOW)
    {
      lcd.print("6");                       // prints '6'
    }
    
  else 
  {
    if(D7==LOW)
    {
      lcd.print("X");                       // prints 'X'
    }
    
   }}}

  digitalWrite(R1,HIGH);                    // Drive R1, R2 to HIGH
  digitalWrite(R2,HIGH);
  digitalWrite(R3,LOW);                     // Drive R3 to LOW
  digitalWrite(R4,HIGH);                    // Drive R4 to HIGH
  D4=digitalRead(C1);                       // sets D4 equal to the input C1
  D5=digitalRead(C2);                       // sets D5 equal to the input C2
  D6=digitalRead(C3);                       // sets D6 equal to the input C3
  D7=digitalRead(C4);                       // sets D7 equal to the input C4
  
  if(D4==LOW)
  {
    lcd.print("1");                         // prints '1'
  }
 
  else
  {
    if(D5==LOW)
    {
      lcd.print("2");                       // prints '2'
    }
   
  else 
  {
    if(D6==LOW)
    {
      lcd.print("3");                       // prints '3'
    }
   
  else 
  { 
    if(D7==LOW)
    {
      lcd.print("-");                       // prints '-'
    }
   }}}
   
  digitalWrite(R1,HIGH);                    // Drive R1, R2, R3 to HIGH
  digitalWrite(R2,HIGH);
  digitalWrite(R3,HIGH);
  digitalWrite(R4,LOW);                     // Drive R4 to LOW
  D4=digitalRead(C1);                       // sets D4 equal to the input C1
  D5=digitalRead(C2);                       // sets D5 equal to the input C2
  D6=digitalRead(C3);                       // sets D6 equal to the input C3
  D7=digitalRead(C4);                       // sets D7 equal to the input C4
  
  if(D4==LOW)
  {
    lcd.print(" ");                         // prints nothing
  }
  
  else
  {
    if(D5==LOW)
    {
      lcd.print("0");                       // prints '0'
    }
    
   else
   {
    if(D6==LOW)
    {
      lcd.print("=");                       // prints '='
    }
    
   else
   {
    if(D7==LOW)
    {
      lcd.print("+");                       // prints '+' 
    }
    
   }}}
   
}