Character conversion string

Transmit the longitude and latitude(labview) to arduino and how to separate
I only could receive character. But I want to receive the entire string.

#include <NewSoftSerial.h>
NewSoftSerial xbee(2,3);
int atoi(const char * str);
double d1,d2;
char sz;
char *pEnd;
int ledPin = 13;
int servopin = 9;
void setup()
{
  pinMode(ledPin,OUTPUT);
  pinMode(servopin,OUTPUT);
  xbee.begin(9600);
  Serial.begin(9600);
 
}

void loop()
{
  if(Serial.available()>0)
  {
    digitalWrite(ledPin,HIGH);
    sz =Serial.read();
    char *pEnd;
    d1=strtod(sz,&pEnd);
    d2=strtod(pEnd,NULL);
    Serial.write(d1);
    Serial.write(d2);   
  
  }
  
}

But I want to receive the entire string.

You have to decide where the string starts, and where the string ends.

This sort of problem comes up every other day here.
There are even libraries to do it.

You need to exercise your search fingers.

    d1=strtod(sz,&pEnd);

According to http://www.cplusplus.com/reference/clibrary/cstdlib/strtod/, the first argument is supposed to be a string - a NULL terminated array of characters, not a character. Of course the output is not what you expect when the input is not what it expects. Pay attention to this sort of thing. It'll bite you in the ass again if you don't.