how can I send a variable to println? this is my method

void mensaje_sms()
{   
  string numero = "777777";  // this is my variable           
  SIM900.print("AT+CMGF=1\r");
  delay(100);
      SIM900.println("AT+CMGS=\"591"numero"\"");
//IM900.println("AT+CMGS=\"59177777777\""); //only in this way does it work
      delay(100);
      SIM900.println("SEND NUMERO VARIABLE RODO");
      delay(100);
      SIM900.println((char)26);
      delay(100);
      SIM900.println();
      delay(5000);
      Serial.println("SMS sent successfully");
    }


how can I send a variable to println?
Change:

SIM900.println("AT+CMGS=\"591"numero"\"");


to

SIM900.print("AT+CMGS=\"591");
SIM900.print(numero);
SIM900.println("\"");


Note that only the final call is to println() (which just prints a carriage-return character at the end.)