If str [ i ] is between 0 and 9 and i is the last occurence in str
else if ( ( str [ i ] >= '0' && str [ i ] <= '9' ) && num [ str [ i ] - 48 ] == i ) { int occ = str [ i ] - 48 ; while ( occ -- ) { res += str [ i ] ; } } else { res += str [ i ] ; } }