I'am trying to apply USSD operation with variable codes, for example this piece of code return my account balance:

             gsm.SimpleWriteln("AT+CUSD=1,\"*100#\""); 

i want to change "*100#" to variable so gsm.SimpleWrite uses what the variable contains. I want to find how to make it work like this:

             gsm.SimpleWriteln("AT+CUSD=1,\"Variable\"");

I'am trying to apply USSD operation with variable codes, for example this piece of code return my account balance:

             gsm.SimpleWriteln("AT+CUSD=1,\"*100#\""); 

i want to change "*100#" to variable so gsm.SimpleWrite uses what the variable contains. I want to find how to make it work like this:

             gsm.SimpleWriteln("AT+CUSD=1,\"Variable\"");

EDIT: here is my code to give you a better view. it return balance in serial monitor.

#include "SIM900.h"



  void setup() 
    {
   Serial.begin(9600);
    Serial.println("GSM Shield testing.");
       if (gsm.begin(9600))
            Serial.println("\nstatus=READY");
      else Serial.println("\nstatus=IDLE");

         gsm.SimpleWriteln("AT+CUSD=1,\"*100#\"");
      delay(10000);
             char msg[200];
             gsm.read(msg, 200);
            Serial.print("resp: ");
            Serial.println(msg);
 }
    void loop()
     {

    }