title: error: #137: expression must be a modifiable lvalue
body: <p>I read all questions on this topic but no one of problems seems like mine. However, i'm getting an error: <em>expression must be a modifiable lvalue</em>. A part of C code where the errors founded is listed bellow.</p>
  
  <pre><code> ws-&gt;fetch_next_state = &amp;deg1_user_init;        
   ws-&gt;back_to_current  = &amp;text_frame_print; 
   ws-&gt;_frame.text_buff[0] = deg_symbol_th; // error line
   ws-&gt;_frame.text_buff[1] = deg_symbol_te; //error line
   ws-&gt;_frame.object_no = 2;                                  
   ws-&gt;objects_counter = 0;`
  </code></pre>
  
  <p>Meaning of the upper code snipet is in passing the pointer of the constant memory area  to the routine which sends the characters to the peripheral device.</p>
  
  <p>objects <code>deg_symbol_th</code> and <code>deg_symbol_te</code> are defined as</p>
  
  <pre><code> char deg[2] = {0xF8, 0x00}; 
   const struct text_object deg_symbol_th = {6,3,2,45,240, deg};
   const struct text_object deg_symbol_te = {6,10,2,265,240, deg};
   const struct text_object deg_symb_svc =  {6,3,2,430,35, deg};
  </code></pre>
  
  <p>and <code>ws-&gt;_frame.text_buff[0]</code> is a part of the structure </p>
  
  <pre><code>struct frame
  {
  enum frame_sta frame_status;
  enum frame_sta frame_status_diff;
  const struct text_object *text_buff;
  const struct box_object  *box_buff;
  const struct area_object *area_buff;
  uint8_t object_no;
  };
  
  
  struct wspace{
     struct netimer       period;
     struct nequeue   deferred;
     struct nevent *  deferred_queue_storage[EPA_EEPROM_QUEUE_SIZE];
     struct nepa *    producer;
     struct event_i2c_transfer        transfer;
     struct text_object   *Val_frame_buffer[15];
     struct frame        _frame;
     naction      (*back_to_current)(struct nsm * sm, const struct nevent * event); 
     naction      (*fetch_next_state)(struct nsm * sm, const struct nevent * event);           
     uint32_t     i2c_retry;
     uint8_t      i2c_buffer[35];
  }ws;
  </code></pre>
  
  <p>What could be the problem? </p>