Keypad Calculator using LCD

1#include <Keypad.h>
2#include <LiquidCrystal.h>
3int Contrast = 120;
4LiquidCrystal  lcd(A1, A2, 13, 12, 11, 10);
5
6const byte ROWS = 4; 
7const byte COLS = 4;  
8int expr[2];
9int i=0;
10char op;
11
12void resetCalc()
13{
14  	Serial.println();
15  	i = 0;
16  	lcd.clear();
17  	lcd.setCursor(0,0);
18}
19char hexaKeys[ROWS][COLS]  = {
20  {'1', '2', '3', 'A'},
21  {'4', '5', '6', 'B'},
22  {'7', '8', '9', 'C'},
23  {'*', '0', '#', 'D'}
24};
25
26byte rowPins[ROWS] = {9, 8, 7, 6}; 
27byte  colPins[COLS] = {5, 4, 3, 2}; 
28
29Keypad customKeypad = Keypad(makeKeymap(hexaKeys),  rowPins, colPins, ROWS, COLS); 
30void setup(){
31  Serial.begin(9600);
32  analogWrite(A0,  Contrast);
33  lcd.begin(16, 2);
34  lcd.noCursor();
35  lcd.setCursor(0,0);
36  Serial.println("Welcome to keypad Calculator");
37  Serial.println("A = +,  B = -, C = *, D = /");
38  Serial.println("Press # to calculate");
39  Serial.println("Press  * to reset");
40  Serial.println("NOTE: It works only on single digit numbers\
41\
42");
43}
44  
45void loop(){
46  char key = customKeypad.getKey();
47  if(key)
48  {
49    if(i == 0)
50    {
51          expr[0] = key-48;
52          Serial.print(expr[0]);
53      	  lcd.print(expr[0]);
54          i++;
55    }
56    else if(i == 1)
57    {
58          op = key;
59      	  i++;
60     	  if(op == 'A')
61          {
62          	Serial.print(" + ");
63            lcd.print(" + ");
64          }
65      	  else if(op == 'B')
66          {
67          	Serial.print(" - ");
68            lcd.print(" - ");
69          }
70          else if(op == 'C')
71          {
72          	Serial.print(" * ");
73            lcd.print(" *  ");
74          }
75          else if(op == 'D')
76          {
77          	Serial.print("  / ");
78            lcd.print(" / ");
79          }
80          else
81          {
82            Serial.println("Syntax error");
83            lcd.print(" Syntax  error ");
84            resetCalc();
85          }
86         
87    }
88    else if(i == 2)
89    {
90          expr[1] = key-48;
91          Serial.print(expr[1]);
92      	  lcd.print(expr[1]);
93      	  Serial.print(" = ");
94      	  lcd.print("  = ");
95          if(op == 'A')
96          {
97            Serial.println(expr[0]  + expr[1]);
98            lcd.print(expr[0] + expr[1]);
99          }
100          else  if(op == 'B')
101          {
102            Serial.println(expr[0] - expr[1]);
103            lcd.print(expr[0] - expr[1]);
104          }
105          else if(op  == 'C')
106          {
107            Serial.println(expr[0] * expr[1]);
108            lcd.print(expr[0]  * expr[1]);
109          }
110          else if(op == 'D')
111          {
112            Serial.println(expr[0]  / expr[1]);
113            lcd.print(expr[0] / expr[1]);
114          }
115
116          i++;
117    }
118    else if(key == '*' || i == 3)
119    {
120      resetCalc();
121    }
122  }
123}