Calculator with 16x2 LCD display and 4x4 keypan

1#include <Keypad.h>
2#include   <LiquidCrystal.h>
3
4LiquidCrystal  lcd(0, 1, 2, 3, 4, 5);
5const byte ROWS = 4;
6const byte COLS = 4;
7
8char  keys [ROWS] [COLS] = {
9  {'1', '2', '3', '+'},
10  {'4', '5', '6', '-'},
11  {'7', '8', '9', '*'},
12  {'C', '0', '=', '/'}
13};
14byte rowPins[ROWS] =  {13,12,11,10};
15byte colPins[COLS] = {9,8,7,6};
16
17Keypad myKeypad = Keypad(  makeKeymap(keys), rowPins, colPins, ROWS, COLS );
18
19boolean presentValue =  false;
20boolean next = false;
21boolean final = false;
22String num1, num2;
23int  answer;
24char op;
25
26void setup()
27{
28  lcd.begin(16,2);
29  lcd.setCursor(0,0);
30  lcd.print("Techtronic Harsh");
31  lcd.setCursor(0,1);
32  lcd.print("   Calculator");
33  delay(3000);
34  lcd.clear();
35  lcd.setCursor(0,0);
36  lcd.print("    Like  And");
37  lcd.setCursor(0,1);
38  lcd.print("  Subscribe Us"    );
39  delay(3000);
40  lcd.clear();
41}
42
43void loop(){
44
45  char key = myKeypad.getKey();
46
47  if (key != NO_KEY && (key=='1'||key=='2'||key=='3'||key=='4'||key=='5'||key=='6'||key=='7'||key=='8'||key=='9'||key=='0'))
48  {
49    if (presentValue != true)
50    {
51      num1 = num1 + key;
52      int  numLength = num1.length();
53      lcd.setCursor(15 - numLength, 0); //to adjust  one whitespace for operator
54      lcd.print(num1);
55    }
56    else 
57    {
58      num2 = num2 + key;
59      int numLength = num2.length();
60      lcd.setCursor(15  - numLength, 1);
61      lcd.print(num2);
62      final = true;
63    }
64  }
65
66  else if (presentValue == false && key != NO_KEY && (key == '/' || key == '*' ||  key == '-' || key == '+'))
67  {
68    if (presentValue == false)
69    {
70      presentValue = true;
71      op = key;
72      lcd.setCursor(15,0);
73      lcd.print(op);
74    }
75  }
76
77  else if (final == true && key != NO_KEY  && key == '='){
78    if (op == '+'){
79      answer = num1.toInt() + num2.toInt();
80    }
81    else if (op == '-'){
82      answer = num1.toInt() - num2.toInt();
83    }
84    else if (op == '*'){
85      answer = num1.toInt() * num2.toInt();
86    }
87    else if (op == '/'){
88      answer = num1.toInt() / num2.toInt();
89    }    
90      lcd.clear();
91      lcd.setCursor(15,0);
92      lcd.autoscroll();
93      lcd.print(answer);
94      lcd.noAutoscroll();
95  }
96  else if (key !=  NO_KEY && key == 'C'){
97    lcd.clear();
98    presentValue = false;
99    final  = false;
100    num1 = "";
101    num2 = "";
102    answer = 0;
103    op =  ' ';
104  }
105}