(1024) : error 017: undefined symbol \"ReturnUser\"
warning 203: symbol is never used: \"IsNumeric\"

ReturnUser(text[], playerid = INVALID_PLAYER_ID)
{
    new pos = 0;
    while (text[pos] < 0x21) // Strip out leading spaces
    {
        if (text[pos] == 0) return INVALID_PLAYER_ID; // No passed text
        pos++;
    }
    new userid = INVALID_PLAYER_ID;
    if (IsNumeric(text[pos])) // Check whole passed string
    {
        userid = strval(text[pos]);
        if (userid >=0 && userid < MAX_PLAYERS)
        {
            if(!IsPlayerConnected(userid))
            {
                userid = INVALID_PLAYER_ID;
            }
            else
            {
                return userid;
            }
        }
    }
    new len = strlen(text[pos]);
    new count = 0;
    new name[MAX_PLAYER_NAME];
    for (new i = 0; i < MAX_PLAYERS; i++)
    {
        if (IsPlayerConnected(i))
        {
            GetPlayerName(i, name, sizeof (name));
            if (strcmp(name, text[pos], true, len) == 0)
            {
         if (len == strlen(name))
         {
            return i;
             }
         else
         {
               count++;
               userid = i;
         }
      }
   }
}
if (count != 1)
{
   if (playerid != INVALID_PLAYER_ID)
    {
       if (count)
      {
         SendClientMessage(playerid, 0xFF0000AA, \"Multiple users found, please narrow earch\");
      }
      else
      {
         SendClientMessage(playerid, 0xFF0000AA, \"No matching user found\");
      }
     }
    userid = INVALID_PLAYER_ID;
}
return userid;
}

IsNumeric(const string[])
{
        for (new i = 0, j = strlen(string); i < j; i++)
        {
                if (string > \'9\' || string < \'0\') return 0;
        }
        return 1;
}

....  = ReturnUser(tmp);