How Converd string to char

Using Arduino Programming Questions
6

To add a char to a string, you must have a string and an index to that string.

char myString[20];
byte myStringIndex;

Then you can add to your string as long as there is still room.

If (myStringIndex < 19) {
  myString[myStringIndex] = inChar;
  myStringIndex++;
}

Whenever you feel like it, you can print the string.

Serial.print (myString);

This is covered in Serial Input Basics.