Build an Electronic Calculator with Arduino

Do you want to know how to make an Electronic Calculator with Arduino mega ? Here it is.

// Electronic Calculator
//Written by Matt Kan
//Instagram : matt_kan1122
//Email : kmat111222333@gmail.com
//Reuse or redistribution is allowed, so long as credit has been given to the original maker


#include <LiquidCrystal.h>

const int RS = 12, EN = 11, D4 = 5, D5 = 4, D6 = 3, D7 = 2;
LiquidCrystal lcd(RS, EN, D4, D5, D6, D7);

int readButtonState[16]; //to initialize all the 16 input buttons from digits 0 to 9 to + - x / = CLR

long output[2]; // the total result = 1st output + 2nd output , for example, result = 111+41 = 152

int digit[7];     // to store the input digits

int addFlag=0; int subFlag=0; int multiFlag=0; int divFlag=0;
//These flags are for the recongition of which button(+ - x /) the user has entered

void setup() {
  Serial.begin(9600);  // You need to enter this code for applying the Serial Monitor,very convenient
  for(int k=14;k<=30;k++)
  {
  pinMode(k,INPUT_PULLUP);
  }
  lcd.begin(16, 2); }

void loop() {
   int i=0;
  long total = 0;

  for(int n=0;n<=16;n++)
  readButtonState[n]=digitalRead(n+14);  //THIS LINE OF CODE MUST BE PUT INSIDE loop()

while((readButtonState[10]==1)&&(readButtonState[11]==1)&&(readButtonState[12]==1)&&(readButtonState[13]==1)&&(readButtonState[14]==1))
 //THIS IS FOR THE STORAGE OF DIGITS INTO AN ARRAY
  {
     for(int n=0;n<=16;n++)
  readButtonState[n]=digitalRead(n+14);
 //THIS LINE OF CODE MUST BE RUN CONTINUOUSLY

  if(readButtonState[15]==0)
  lcd.clear();
 
  for(int a=0;a<=9;a++)                      //Element 0 to 9 : digit 0 to 9
  {                                                       //Element 10 to 13: + - x /   ,ie digital pins 24 to 27
if(readButtonState[a]==0)                 //Element 14 to 15 : = CLR     ,ie digital pins 28 to 29
{
 
   lcd.print(a);
   digit[i]=a;                       
   ++i;               
 
   delay(330);
}//End of if 
  }//End of For loop
}//End of While loop for the storage of digits into an array

   if(readButtonState[10]==0)
  {
    lcd.print("+");
    for(int m=0;m<i;m++)
    {
    output[0]+=digit[m]*power(10,i-1-m);  //output is tested ok
    delay(300);
    }
    addFlag=1;
}//End of + If Statement

if(readButtonState[11]==0)
  {
   lcd.print("-");
    for(int m=0;m<i;m++)
    {
     output[0]+=digit[m]*power(10,i-1-m);  //output is tested ok
    delay(300);
    }
    subFlag=1;
 }//End of - If Statement

if(readButtonState[12]==0)
  {
    lcd.print("x");
    for(int m=0;m<i;m++)
    {
     output[0]+=digit[m]*power(10,i-1-m);  //output is tested ok
    delay(300);
    }
    multiFlag=1;
 }//End of x If Statement

if(readButtonState[13]==0)
  {
    lcd.print("/");
    for(int m=0;m<i;m++)
    {
     output[0]+=digit[m]*power(10,i-1-m);  //output is tested ok
    delay(300);
    }
    divFlag=1;
 }//End of / If Statement

if(readButtonState[14]==0)   //If Statement of =
{
for(int m=0;m<i;m++)
    {
    output[1]+=digit[m]*power(10,i-1-m);  //output is tested ok
    delay(300);
    }
     if(addFlag==1)
     total=output[0] + output[1];
     if(subFlag==1)
     total=output[0] - output[1];
     if(multiFlag==1)
     total=output[0] * output[1];
     if(divFlag==1)
     total=output[0] / output[1];

     lcd.setCursor(0,1);
     lcd.print("=");
     lcd.print(total);
     addFlag=0; subFlag=0; multiFlag=0; divFlag=0;
     total=0; output[0]=0; output[1]=0;
}}

 long power(int base,int exponent)
{
  long result=10;

  for(int i=1;i<exponent;i++){
  result=result*base;}
  if(exponent==0)
  result=1;
  return result;
}