[RESOLVED] Issue with stream extraction

[david16]

So if I want to validate a single character input I was trying something like that

char ch;
 
 do {
	
	   cout << "\nPlease enter a single character :\n " << endl;
	   getline ( cin ,ch );

	}while ( ch.length != 1 && cout <<" Wrong input ! " );

I want the user to enter a single character only if not it will tell him to reenter you see ?

[2kaud]

}while ( ch.length() != 1 && cout <<" Wrong input ! " );

Once the syntax is correct, this will accept a single char terminated by a <newline>.

.length() is a member function of class string - not a member variable!

[david16]

it worked but first time before even input it shows wrong input why ?


this is from cmd

Please enter a single character of your choice :

// didnt input yet !

Sorry Wrong input !

Please enter a single character of your choice :

[2kaud]

#include <iostream>
#include <string>
using namespace std;

int main()
{
	string ch;

	do {

		cout << "\nPlease enter a single character :\n " << endl;
		getline(cin, ch);

	} while (ch.length() != 1 && cout << " Wrong input ! ");
}

Works for me OK.

c:\MyProgs>test12

Please enter a single character :

qq
 Wrong input !
Please enter a single character :

q

c:\MyProgs>

[david16]

I have another do while statement before this validation when I remove it everything is fine . But when I add it I get wrong input first then the message "please enter a single character "..... they are 2 separate do while why they are affect each other ?

[david16]

int x;

 do {
	
	   cout << "\nPlease enter number ( > 2 ) :\n " << endl;
	   cin >> x;

   }while ( x < 2 && cout << "\nSorry wrong input!\n " );

string ch;

	do {

		cout << "\nPlease enter a single character :\n " << endl;
		getline(cin, ch);

	} while (ch.length() != 1 && cout << " Wrong input ! ");

try both together it will not work prorperly

[2kaud]

You are mixing stream extraction (>>) with getline(). >> doesn't remove the ending <newline> because >> ignores all white-space found before input. getline() obtains the data from the stream and removes the training <newline>. So if you have >> followed by getline(), the getline() gets the <newline> left over from the >> and sets the value to "" (empty) which has a length of 0. Hence the issue you are finding.

What you need to do is after the first do loop, remove the remaining <newline>. Try

cin.ignore(1000, '\n');

between the two do loops.

[david16]

Oh I see now what's the problem . thx got it work fine now

[2kaud]

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