how to limit text and loops.

[stunnahayes]

Ok I am making a program that the user has to enter up to 8 digits to make a binary number so it they have to be 0 or 1. I need help in 2 spots how do I limit cin to only allow user to input up to 8 characters. and cant get my loops to work right.

// InvalidBinDr.cpp 

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

// FILL IN InvalidBin PROTOTYPE: 

 
int main()
{
	// Variables local to main
	bool inValid=true;	// True if an invalid binary # is entered
	string strVal;	// The user entered string



	cout << "Please enter a string." << endl;
	cin >> strVal;
	

	if(inValid)
		cout << strVal << " is not a binary number." << endl;
	else
		cout << strVal << " is a binary number." << endl;
	while(strVal=="0" || strVal=="1")


	return 0;
}

// FUNCTION InvalidBin RETURNS TRUE IF THE STRING ENTERED BY THE
// USER DOES NOT REPRESENT A VALID 8-BIT BINARY NUMBER OTHERWISE
// IT RETURNS FALSE, (i.e. the string has 8 bits that are 1's or 
// 0's only).

[stunnahayes]

help anyone?

[rossipoo]

You can use string.length() to check the length. And to check for symbols other than 0 and 1 you'll need to iterate the string one character at a time checking for characters you don't allow. if (string[i]!='0' && string[i]!='1')

[PanGalactic]

You cannot limit the number of characters a user inputs. You can either ignore the extra characters or tell the user their input is wrong and ask them to re-enter it.

string input;
while (true) {
    cout << "Enter a binary number (8 digits or less): ";
    getline(cin, input);
    if (input.size() <= 8) break;
    cerr << "You entered more than 8 digits.  Please re-enter your number." << endl;
}

If you edit your post and put code tags around your code, it will be more legible.

[stunnahayes]

ok so I have

// InvalidBinDr.cpp 

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

// FILL IN InvalidBin PROTOTYPE: 

 
int main()
{
	// Variables local to main
	bool inValid=true;	// True if an invalid binary # is entered
	char strVal;	// The user entered string



string input;
while (true) {
    cout << "Enter a binary number (8 digits or less): ";
    getline(cin, input);
    if (input.size() <= 8) break;
    cerr << "You entered more than 8 digits.  Please re-enter your number." << endl;
}
cin >> strVal;


	if(inValid)
		cout << strVal << " is not a binary number." << endl;
	else
		cout << strVal << " is a binary number." << endl;



	return 0;
}

// FUNCTION InvalidBin RETURNS TRUE IF THE STRING ENTERED BY THE
// USER DOES NOT REPRESENT A VALID 8-BIT BINARY NUMBER OTHERWISE
// IT RETURNS FALSE, (i.e. the string has 8 bits that are 1's or 
// 0's only).

Now Can someone help me with my loops/if statement so if user inputs the correct one it says not right cout instead of the same one over and over.

[Duthomhas]

I will typically have something like

cout << "Please enter foo> " << flush;
while (true)
  {
  getline( cin, foo );
  if (valid( foo )) break;
  cout << "Foo must have quux to be valid.\nPlease enter foo> " << flush;
  }
cout << "Thank you for entering a valid foo.\n";

This, of course, is an example. The specifics will vary depending on what foo is and how it is validated.

Hope this helps.

[stunnahayes]

hmm still not fixed

// InvalidBinDr.cpp 

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

// FILL IN InvalidBin PROTOTYPE: 

 
int main()
{
	// Variables local to main
	bool inValid=true;	// True if an invalid binary # is entered
	string input;// The user entered string

while (true) {
    cout << "Enter a binary number (8 digits or less): ";
    getline(cin, input);
    if (input.size() <= 8) break;
    cerr << "You entered more than 8 digits.  Please re-enter your number." << endl;
}

   while (true)
  {
  getline( cin, input );
  if (inValid) break;
  cout << "Thank you for entering a valid input.\n" << endl;
   }
cout << "input must be 0's or 1's to be valid.\nPlease enter input> " << flush;


	return 0;
}

/*
Enter a binary number (8 digits or less): 10101010

input must be 0's or 1's to be valid.
Please enter input> Press any key to continue . . .
*/

/*
Enter a binary number (8 digits or less): 12345678

input must be 0's or 1's to be valid.
Please enter input> Press any key to continue . . .
*/

[hoshiro]

my suggestion is this the code will be cleaner this way:

do {
cin >> a;

if(a.size() > 8)
cerr << "You entered more than 8 digits. Please re-enter your number." << endl;

} while(a.size() > 8);
cout << "Thank you for entering a valid input.\n" << endl;

so it will solve all the code cause it's kinda messy your way(23 lines vs. 5)

[Duthomhas]

Get rid of lines 24 through 30.

You need to test all of your conditions at line 20. Currently you are only checking the length. I suggest you use string::find_first_not_of() to check against non binary characters.

20 if ((input.size() <= 8) && (input.find_first_not_of( "01" ) == string::npos)) break;

Remember, get the input, check it, and then continue.
You cannot get the same input multiple times...

Hope this helps.

@hoshiro
Please pay attention to the previous responses in this thread...