#include <Keypad.h>
float x1, x2;
char c;
const byte ROWS = 4; // Four rows
const byte COLS = 4; // Four columns
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() {
  for (int i = 0; i < 3; i++) {
    char key = keypad.getKey();
    if (key) {
      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(c=='*'){
    Serial.println(x1*x2);
  }

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

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

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

}