#include <Keypad.h>
float x1, x2,out;
char c;
const byte ROWS = 4; // Four rows
const byte COLS = 4; // Four columns
char key;
char keys[ROWS][COLS] = {
  {'1', '2', '3', 'A'},
  {'4', '5', '6', 'B'},
  {'7', '8', '9', 'C'},
  {'*', '/', '+', '-'}
};
byte rowPins[ROWS] = {9, 8, 7, 6}; // Connect to the row pinouts of the keypad
byte colPins[COLS] = {5, 4, 3, 2}; // Connect to the column pinouts of the keypad

Keypad keypad = Keypad(makeKeymap(keys), rowPins, colPins, ROWS, COLS);

void setup() {
  Serial.begin(9600);
}

void loop() {
  Serial.println("");
  Serial.println("NEW OPERATION");
  for (int i = 0; i < 3; i++) {
    key = keypad.getKey();
    if (key) {
      if(key=='C'){
    loop();
    break;
    
  }
      
      Serial.print(key);
      if (i == 0) {
        x1 = int(key) - 48;
      }
      if (i == 1) {
        c = key;
      }
      if (i == 2) {
        x2 = int(key) - 48;
        Serial.print(" = ");
      }
    }
    else {
      i--;
    }
  }
  
  if((x1<0||x1>9)||(x2<0||x2>9)||!(c=='*'||c=='/'||c=='+'||c=='-')){
Serial.println("WRONG INPUT!!!");
loop();
  }
  if(c=='*'){
    Serial.println(out=x1*x2);
  }

  if(c=='/'){
    Serial.println(out=x1/x2);
  }

  if(c=='+'){
    Serial.println(out=x1+x2);
  }

  if(c=='-'){
    Serial.println(out=x1-x2);
  }

  while(1){
     Serial.print(out);   
  for (int i = 1; i < 3; i++) {

    key = keypad.getKey();
    if (key) {
      if(key=='C'){
        loop();
        break;
        
      }
      Serial.print(key);
      if (i == 1) {
        c = key;
      }
      if (i == 2) {
        x2 = int(key) - 48;
        Serial.print(" = ");
      }
    }
    else {
      i--;
    }
  }

  if((x2<0||x2>9)||!(c=='*'||c=='/'||c=='+'||c=='-')){
Serial.println("WRONG INPUT!!!");
loop();
  }
  if(c=='*'){
    Serial.println(out=out*x2);
  }

  if(c=='/'){
    Serial.println(out=out/x2);
  }

  if(c=='+'){
    Serial.println(out=out+x2);
  }

  if(c=='-'){
    Serial.println(out=out-x2);
  }}
  

}