/*
Função atoi
*/

String n1 = "12";
String n2 = "34";

void setup() {

  Serial.begin(9600);

  int N1 = n1.toInt();
  int N2 = n2.toInt();

  int N = N1 + N2;

  Serial.print(n1);
  Serial.print("+");
  Serial.print(n2);
  Serial.print("=");
  Serial.println(N);  
}

void loop() {
  // put your main code here, to run repeatedly:

}