I want to send gps data through sim900 but i don't know why the code doesn't work i want your help please

#include <SoftwareSerial.h>
#include <TinyGPS++.h>

SoftwareSerial sim(7, 8);
int _timeout;
String _buffer;
String number1 = "+212684547105";
String number = "+xxxxxxxxxxxx"; //-> change with your number

// Choose two Arduino pins to use for software serial
int RXPin = 2;
int TXPin = 3;

int GPSBaud = 9600;

// Create a TinyGPS++ object
TinyGPSPlus gps;

// Create a software serial port called "gpsSerial"
SoftwareSerial gpsSerial(RXPin, TXPin);
//SoftwareSerial espSerial(0, 1);
String str;


void setup() {
  //delay(7000); //delay for 7 seconds to make sure the modules get the signal
  Serial.begin(9600);
  _buffer.reserve(50);
  Serial.println("Sistem Started...");
  sim.begin(9600);
  delay(1000);
  Serial.println("Type s to send an SMS, r to receive an SMS, and c to make a call");

  // Start the Arduino hardware serial port at 9600 baud


  // Start the software serial port at the GPS's default baud
  gpsSerial.begin(GPSBaud);
}
void loop() {

 float lati,longi,Alti;
  // This sketch displays information every time a new sentence is correctly encoded.
  while (gpsSerial.available() > 0)
    if (gps.encode(gpsSerial.read())){
       if (gps.location.isValid())
  {
    lati = gps.location.lat();
    longi = gps.location.lng();
    Alti = gps.altitude.meters();
    str ="Latitude: " +String(lati)+ "longitude: " +String(longi)+ "Altitude: "+String(Alti); 
    sim.println("AT+CMGF=1\r");    //Sets the GSM Module in Text Mode
    delay(200);
  //Serial.println ("Set SMS Number");
    sim.println("AT+CMGS=\"" + number + "\"\r"); //Mobile phone number to send message
    delay(200);
    sim.println(str);
    delay(1000);
    sim.println((char)26);// ASCII code of CTRL+Z
    delay(200);
    _buffer = _readSerial();
  }
  else
  {
    Serial.println("Location: Not Available");
  }
 
    }
  // If 5000 milliseconds pass and there are no characters coming in
  // over the software serial port, show a "No GPS detected" error
  if (millis() > 5000 && gps.charsProcessed() < 10)
  {
    Serial.println("No GPS detected");
    while(true);
  }
}

String _readSerial() {
  _timeout = 0;
  while  (!sim.available() && _timeout < 12000  )
  {
    delay(13);
    _timeout++;
  }
  if (sim.available()) {
    return sim.readString();
  }
}