float input1;
char calc;
float input2;
float answer;

void setup() {
  Serial.begin(9600);
  Serial.println("Welcome to calculation software!");
}

void loop() {
  Serial.println("Now please enter number.");
  if (Serial.available()) {
    input1 = Serial.readStringUntil(0x0a);
  }
  Serial.println("Next, please enter calculation feature.");
  Serial.println("Available : +, -, *, /, %, sin, soc, tan, pow, abs, sqrt"); //%:除法の余り　abs:絶対値　pow:べき乗　sprt:平方根
  Serial.println("%:Remainder of division, abs:Absolute value, pow:Powe, sqrt:Square root");
  if (Serial.available()) {
    String calc = String(Serial.readStringUntil(0x0a));
  }

  Serial.println("Finaly, please enter second number.");
  if (Serial.available()) {
    input2 = Serial.readStringUntil(0x0a);
  }

  if (calc != "+" | calc != "-" | calc != "*" | calc != "/" | calc != "%") {
    answer = input1 * calc(input2);
    Serial.print(input1, calc);
    Serial.print("(");
    Serial.print(input2);
    Serial.println(")");
  }
}