Passing string to uint8_t array in arduino

I have to send an integer counter as 'num' through XBee (in API mode) from Arduino. For this purpose I have to convert this integer to String and then to uint8_t array as it is needed in API frame to transmit.

Apart from other details I've converted my integer to string like

  String str;
  int num = 0;
  char  cstr[16];

void loop() {
  num++;
  str = String(num);
  str.toCharArray(cstr,16);

  Serial.println(cstr);  // this shows the correct result, means int is converted to String correctly

  uint8_t data[] = {cstr}; // passing String to uint8_t array

  XBeeAddress64 addr64 = XBeeAddress64();
  addr64.setMsb(0x00000000);
  addr64.setLsb(0x00000000); 
  ZBTxRequest zbTx = ZBTxRequest(addr64, data, sizeof(data));
  xbee.send(zbTx);

  int count = sizeof(data);
    for (int i = 0; i < count; i++) {
      if (i == (count-1)) {
      Serial.print(data[i]);   // here it prints "104" of ASCII which is equal to "h"       
      }
    } 
}

It also transmit it as like that Serial print i.e. ('104'). Please point out if I am making any mistake and guide me if I didn't do it as required.

First get rid of those cstr and String:

 int num = 0;
 //char  cstr[16];
  char data[16] = {'\0'}; // Initialize data array 

void setup() {
}    
void loop() {

 num++;
 //str = String(num);
//str.toCharArray(cstr,16);
 itoa (num, data, 10); 

  Serial.println(data); 
  // To get the number of elements in the array use
  uint8_t datalen = strlen(data);
  // Black box see lib for details
  XBeeAddress64 addr64 = XBeeAddress64();
  addr64.setMsb(0x00000000);
  addr64.setLsb(0x00000000); 
  ZBTxRequest zbTx = ZBTxRequest(addr64, data, datalen);
  xbee.send(zbTx);
 // Print test
  Serial.println("Content of data: ");
  Serial.print(data);
  Serial.print(" datalen: ");
  Serial.print(datalen);
}

This should work as you expect.
To copy an array you would use strcpy (or memcopy with malloc and free), to get the number of elements use strlen.

EDIT: Here is a tested code (just copy andpaste and first replace only the include to your xbee lib:

   #include "Xbee.h"    //-> Change to your xbee lib   

  uint16_t num = 0;
 char xdata[16] =  {'\0'};// Initialize data array
 char numbuf[16] =  {'\0'}; // initialize number buffer
 long currentMillis = 0;

 void setup() {
 Serial.begin(115200);
 currentMillis = millis();

}
void loop() {

 if (millis() - currentMillis > 1000) { // 1 sec timer to prevent overflow due to hammering xbee with data -> tune to your stable transmission
   num++;
   itoa (num, numbuf, 10);     // Num buffer 
   strcpy(xdata, numbuf);      // Copy content of num buffer to data array 
   Serial.println(xdata);

 // To get the number of elements in the array use
   uint16_t datalen = strlen(xdata); 
   // Black box see lib for details
     XBeeAddress64 addr64 = XBeeAddress64();
    addr64.setMsb(0x00000000);
    addr64.setLsb(0x00000000);
    ZBTxRequest zbTx = ZBTxRequest(addr64, data, datalen);
    xbee.send(zbTx);
   // Print test
   Serial.print("Content of xdata: ");
   Serial.print(xdata);
   Serial.print(" datalen: ");
   Serial.println(datalen);
   currentMillis = millis();   // reset timer
 }
}

The result in serial monitor is:

 1
 Content of xdata: 1 datalen: 1
 2
 Content of xdata: 2 datalen: 1
 3
 Content of xdata: 3 datalen: 1
 4
 Content of xdata: 4 datalen: 1
 ....
 864
 Content of xdata: 864 datalen: 3
 865
 Content of xdata: 865 datalen: 3
 866
 Content of xdata: 866 datalen: 3

So all works as expected, no 104 or similar. Please first copy paste - test it - and then your additions