Thread: Quest...?

Have you considered why you're doing this? A program shouldn't go into a failure state unless the input given cannot be used in normal processing. If you have the proper input followed by extraneous data, the program can still run normally. So you should rather be working on ways to handle the extra data if it would effect future input to the program. The simplest solution would be to throw it away.

Code:

#include <iostream>
#include <limits>
#include <string>

using namespace std;

struct seat_number {
  int row;
  char seat;
};

bool get_seat ( istream& in, seat_number& sn )
{
  const string seats ( "abcdef" );

  if ( !( in>> sn.row ) || !in.get ( sn.seat ) )
    return false;
  if ( sn.row < 0 || sn.row > 13 || seats.find ( sn.seat ) == string::npos )
    return false;
  return true;
}

int main()
{
  seat_number sn;

  cout<<"Enter seat number: ";
  for ( ; ; ) {
    if ( get_seat ( cin, sn ) )
      cout<<"You chose "<< sn.row << sn.seat <<endl;
    else {
      cin.clear();
      cin.ignore ( numeric_limits<streamsize>::max(), '\n' );
      cerr<<"Input error\n";
    }
  }
}

>My problem is if the user enters something like (number and more than one letter) 5adffe the user should get an error.

To me a completely different approach could be used to answer the above question. That is, to determine if the input (for example 5adffe) is in error you could accept the input as a single string. If the string is longer than 3 char or shorter than 2 char then it is an error. Then look at each char of string. All char should be alphanum. If not there was an error. If the first char (or two char of the input string if the string is 3 char long) is/are not digits then it is an error. If it is okay, then convert the digits to an int by converting the original string into two strings using abcdef as the parsing spots and converting the first string into an int. If the int is less than 0 or greater than 13 then it is an error. If there is more than 1 letter in the string then it is an error. If the letter is not between a and f then it is an error.

I believe that >> will stop input into a numeric variable such as int when the first non digit char is encountered. Therefore parsing user input with >> will probably parse the leading digits from the letters for you. A call to get() will then get a single char from the input buffer for you, if there is one. However, it won't tell you if there is more than one char in the input buffer, which is what's needed to determine that 5ab or 5adffe are errors.

Maybe rather than using a call to get() you could use another call to >> to a string variable. Then if the string variable was longer than 1 it is an error and if the first char of the string isn't between a and f it is an error. That may be the easiest way to do this.

Oh, well, just my thoughts on an algorhythm to use to answer the question of whether 5adffe is an error. Use at your discretion.

Code:

	char ch;
	p.row =14;
	p.column ='g';
	while((ch!='\n')|| ((p.row >13) || (p.column >'f')))
	{
		cout << "Enter seat (11f): ";
		cin >> p.row;
		cin.clear();
		cin>>p.column;
		ch=cin.get();

		if(ch!='\n')  //added code
		cin.ignore( numeric_limits<streamsize>::max(), '\n' );


	}
		cout<<p.row  <<p.column <<endl;

oops had to edit code so whenn user enters long string of letters and then a valid 11f it wouldn't cycle through the loop