The arrow keys were encoded by three characters in Ubuntu. So I changed my code like this to check arrow keys.
if(kbhit()){
switch(getch()){
case 0x1b: //For case arrow pressed
if(getch() == 0x5b){
switch(getch()){
case 0x41:
turn();
break;
case 0x44:
mv_left();
break;
case 0x43:
mv_right();
break;
case 0x42:
mv_down();
break;
}
}
break;
}
}