Send sms and receive it

how to send an SMS and answer the message using two GSM module?

here is my code snippet but how should I make this program so that it can receive an SMS too?

#include <GSM.h>

#define PINNUMBER “”

// initialize the library instance
GSM gsmAccess; // include a ‘true’ parameter for debug enabled
GSM_SMS sms;

// char array of the telephone number to send SMS
// change the number 1-212-555-1212 to a number
// you have access to
char remoteNumber[20]= “xxxxxxx”;
int sensor=A1;
float temp_read,temp,a;
// char array of the message
char txtMsg[200]=“hello”;

void setup()
{
pinMode(sensor,INPUT);
// initialize serial communications
Serial.begin(9600);

Serial.println(“SMS Messages Sender”);

// connection state
boolean notConnected = true;

// Start GSM shield
// If your SIM has PIN, pass it as a parameter of begin() in quotes
while(notConnected)
{
if(gsmAccess.begin(PINNUMBER)==GSM_READY)
notConnected = false;
else
{
Serial.println(“Not connected”);
delay(1000);
}
}
Serial.println(“GSM initialized”);
sendSMS();
}

void loop()
{
// nothing to see here
}

void sendSMS(){

// sms text
Serial.println(“SENDING”);
Serial.println();
Serial.println(“Message:”);
Serial.println(txtMsg);

// send the message
sms.beginSMS(remoteNumber);
sms.print( txtMsg);
sms.endSMS();
Serial.println("\nCOMPLETE!\n");
}

please help me.

same as his other post https://forum.arduino.cc/index.php?topic=534726.msg3645086#msg3645086

.

the other is ejuste the sends but here he can send and receive an SMS