Best alternatives to convert String to int efficiently

[Idahowalker]

@sdg123

String myString((char *)0);
byte num;
void setup() {
  // put your setup code here, to run once:
  Serial.begin(115200);
  myString.reserve(50);
  //Case 1 
  myString = "H15";
  myString[0] = 0; 
  num = myString.toInt();

myString[0] = 0; <<<< What's that? You want to add a 0 to the end of the String? Use myString.concate( "0" );