cin.ignore

Xiangbuilder · 10-07-2003, 11:35 PM

Recently, I find a new problem in my previous posts, I start a new thead.

Code:

#include<iostream>
using namespace std;
const int size = 11;
void min ();
void try_again ();

int main () {
   cout<<"First, please let me say: best regards to you."
       <<"The program is run to guess a clase that contains two words, "
       <<"that contains eleven letter. Only the first one is capital. "
       <<"You could type a space between the two words, and finally, enter. "<<endl;
   min ();
}

void min () {
   char input[size];
   char result[] = "Best regards";
   char c;
   cout<<"Okay, now, give it a go->:";
   for (int i=0; i<size; i++) //initialize the array
      cin.get(input[i]);
   for (int i=0; i<size; i++) //compare with the result
      if (input[i]==result[i])
         cout<<"Letter "<<i+1<<" is good"<<endl;
      else
         cout<<"Sorry for letter "<<i+1<<endl;
   cin.ignore ();  //the cin is used to filter extra letters
   cout<<"Do you want ot try again, yet? y for yes, n for no."<<endl;
   try_again ();
}

void try_again () {
   char s;
   cin>>s;             
   cin.ignore ();  //the cin is used to filter extra letters
   if (s=='y')
      min ();
   else if (s=='n')
      exit (0);
   else
   {
      cout<<"Please enter y, or n:";
      try_again ();
   }
}
[root@localhost regards_b]# ./min_h
First, please let me say: best regards to you.The program is run to guess a clase that contains two words, that contains eleven letter. Only the first one is capital. You could type a space between the two words, and finally, enter.
Okay, now, give it a go->:Best regardsZ
Letter 1is good.
Letter 2is good.
Letter 3is good.
Letter 4is good.
Letter 5is good.
Letter 6is good.
Letter 7is good.
Letter 8is good.
Letter 9is good.
Letter 10is good.
Letter 11is good.
Do you want ot try again, yet? y for yes, n for no.
Please enter y, or n:ZZZ
Please enter y, or nPlease enter y, or n::n
[root@localhost regards_b]#

I want to use the first cin.ignore to throw out the letters that are after the eleventh one, but it doesn't. The letters that after the eleventh one have been accepted in try_again function.
I want to use the second cin.ignore to throw out the extra letters of the seonc cin, it doesn't too.
How to achieve my purpose?
Thank you.

dakensta · 10-08-2003, 06:52 AM

The prototype for ignore is this:

istream& ignore ( streamsize n = 1, int delim = EOF );

Its purpose is to extract (and discard) n characters, up to and including delim. Extraction stops at whatever limit is reached first.

So ... you need to add some arguments or you are just going to ignore a single character.

Just plucking some possible values at random, you could try std::numeric_limits<std::streamsize>::max() and '\n'.

Xiangbuilder · 10-08-2003, 08:02 AM

Thank you.
How to ignore all user's inputs between the twelfth one and the first enter?
I guess the difficult is the user's inputs is random.

dakensta · 10-08-2003, 08:38 AM

How to ignore all user's inputs between the twelfth one and the first enter?

If I understand correctly, then this is what you are already doing (if you used my earlier suggestion!):

When you call cin.get( ... ) or cin >> s - what you are doing here is asking for a character to be read from a buffer that is connected to the standard input (probably the terminal in which you are running the program).

The user has to put something here and has to signal to the program that something has been put there - in this case you want to use the alphanumeric keys followed by 'return' but it could be a file, output from another program, or anything that can be directed to stdin.

The calls to get( ... ) or cin >> s; will grab from this entered text a single character each. You make 11 calls to get( ... ), thus moving 11 characters from the buffer to the argument supplied to get( .. ).

Everything else in that buffer is, as far as you are concerned, junk and junk you want to get rid of. This is what the call to cin.ignore( ... ) does.

cin.ignore( numeric_limits<streamsize>::max(), '\n' ) will discard every character sitting in the buffer, up to and including the character at which it encounters your 'return' key press (seen as '\n' character).

Hope this helps but if this doesn't clarify things, can you post an example of how things are unsatisfactory?

Xiangbuilder · 10-08-2003, 07:57 PM

Thank you for your patience.
I modify

Code:

cin.ignore ();

to

Code:

cin.ignore( numeric_limits<streamsize>::max(), '\n' )

It works well.
Thank you.
Very helpful.