cin.getline problems

[mconn86]

hi, im relativly new to C++, im just starting to write a simple program where i get the user to read in a string of characters.Im keeping it very simple at first so I can modify it later to use in my program, where I'm having problems is when I ask the user if they want to try again, the computer still holds the value of the original array in its memory and this causes the whole program to go a bit crazy. I think i should be using a cin.ignore statement or something like that but im not too sure how. You can view my program below (very basic,just want to get my head around the idea). Nyone out there with any advice,cheers!

#include <iostream.h>

main_program();

int main()
{

main_program();

return 0;
}

main program()
{
char code[14];
char reply;

cout << "Please enter your code" << endl;
cin.getline (code,14);
cout << code << endl;
cout << "Go again?" << endl;
cin >> reply;
 if (reply =='y')
    {
     main_program();
     }
return 0;
}

[Valmont]

Yes, there is a lot of info on this site about streams. Use the "search" button and try to search for "clearing stream", or something like that.

Also your main_program() function doesn't have a return type. Should be void at least.

[mconn86]

im not woried about the void in my function just forgot putting that in just really want to find out how to clear my array,cant find anything on this site that has helped me so far,ive been experimenting with the following code and it achieves kinda what im looking for as long as i enter the maximum number of characters im my array.
#include <iostream.h>

int main()
{

char code[14];

cout << "Type code" << endl;
cin.getline (code,14);
cout << code << endl;
cin.ignore();
cout << "Enter another code" << endl;
cin.getline (code,14);
cout << code << endl;

return 0;
}

This program works fine as long as the full value of the array is entered i.e 13 characters

[Valmont]

...cant find anything on this site that has helped me so far...

This forum offers some neat solutions when it comes to streams. This is one of them:

#include <iostream>
#include <climits>

//--
using std::endl;
using std::cout;
using std::cin;
//--

void reset_istream() 
{
  if(cin.eof())
  {
    cin.clear(); 
  } else 
  {   
    cin.clear(); 
    cin.ignore(std::numeric_limits<std::streamsize>::max(), '\n');   
  } 
} 

//---------------------------------------

int main()
{
  char code[14];
  char reply;
  cout << "Please enter your code" << endl;
  cin.getline (code,14);
  cout << code << endl;
  cout << "Go again?" << endl;
  cin >> reply;
  if (reply =='y')
  {
  }
  reset_istream();
return 0;

}

[mconn86]

Notice the

so far...

! Thats looks a bit further than ive learned so far, im doing a project in university so I might look a bit suspicious if i used that,I will have a good look at it though think I can understand most of it.Nyway I think ive found a solution that works,not sure how it does but it seems to do the trick.Time will tell...!
Cheers

[Valmont]

Aren't you allowed to study ahead in the university?

Ok. This part is all that you need right now. The other half is usefull in more complex situations where escape sequences are used to terminate input with CTRL+Z/X.

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

cin.clear();
First we clear the stream in case some error occured. Let's start with a blank sheet.

cin.ignore(...
We are going to ignore a certain amount of stuff left in the stream.

std::numeric_limits<std::streamsize>::max()
How much are we going to ignore? Well, let's ignore the maximum number of items a stream can have...

'\n'
...until we find a newline.

#include <climits>
But to use the nice feature of numeric_limits<>max(), we need to include this header.

std::
Let's use definitions only defined by the ISO C++ standard.


using std::endl;
using std::cout;
using std::cin;

It is handy if these often used functions (endl, cout, and cin), can be typed without typing "std::" in front of it all the time. So let's predefine that we want to use the ISO C++ versions only.
Next time when we type "cout<<", the compiler knows we mean the ISO version "std::cout<<".

Another way

void reset_istream(std::istream & is)
{
  char ch;
  // Reset the state.
  is.clear();
  // Remove all characters until we find a newline or EOF.
  ch = is.get();
  while ((ch != '\n')&&(ch != EOF))
    ch = is.get();
  is.clear();
}

Use it like this:

reset_istream(std::cin);