how to change readUnsigned from storing numbers to storing letters

void readstring(char str[], char len) {
    char index = 0;
   while (index < len-1)
   {
      // if waiting read
      while (serial.available()== 0){}
      {
         char c = serial.read();
         // press enter
         if (c == '\r')
         {
            break;
         }

         else
         {
            //stores characters array
            str[index] = c;
            //adds index 1 characters
            //ensures when character pressed,
            //the character visible in serial-mon instead of 0
            index += 1;
            serial.print(c);
         }
      }
   }
   //marks end of string.
   str[index] = '\0';
}   
uint8_t readunsigned() {
      //an array store 8bit integars
      char str[8];
      readstring(str,8);
      //returns integar
      return atol(str);
   }

what receiving , trying store?
give example.

/mogens

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