Can not add line feed to string - arduino

Question

I have an Arduino Leonardo and trying to use it as a serial to USB converter. On Serial1 I have a string ending on a number. This number I'm trying to get via USB to the PC. It works very fine but I need a '\n' at the end and I don't know how. When I try it in the line Keyboard.println or Keyboard.write, I get a various number of lines with the expected number in splitted.
#include <Keyboard.h>
String myEAN ="";
const int myPuffergrosse = 50;
char serialBuffer[myPuffergrosse];
void setup() {
Keyboard.begin();
Serial1.begin(9600);
delay(1000);
}
String getEAN (char *stringWithInt)
// returns a number from the string (positive numbers only!)
{
char *tail;
// skip non-digits
while ((!isdigit (*stringWithInt))&&(*stringWithInt!=0)) stringWithInt++;
return(stringWithInt);
}
void loop() {
// Puffer mit Nullbytes fuellen und dadurch loeschen
memset(serialBuffer,0,sizeof(myPuffergrosse));
if ( Serial1.available() ) {
int incount = 0;
while (Serial1.available()) {
serialBuffer[incount++] = Serial1.read();
}
serialBuffer[incount] = '\0'; // puts an end on the string
myEAN=getEAN(serialBuffer);
//Keyboard.write(0x0d); // that's a CR
//Keyboard.write(0x0a); // that's a LF
}
}

Answer 1

Since myEAN is a String, simply add the character...
myEAN += '\n';
Or, for a full carriage return/line feed combination:
myEAN += "\r\n";
See the doc: https://www.arduino.cc/en/Tutorial/StringAppendOperator
I suggest you use String in your getEAN function as well...
String getEAN(String s)
{
// returns the first positive integer found in the string.
int first, last;
for (first = 0; first < s.length(); ++first)
{
if ('0' <= s[first] && s[first] <= '9')
break;
}
if (first >= s.length())
return "";
// remove trailing non-numeric chars.
for (last = first + 1; last < s.length(); ++last)
{
if (s[last] < '0' || '9' < s[last])
break;
}
return s.substring(first, last - 1);
}