why is this not working

Hello

I have this code

Code:

#include <iomanip>
#include <ios>
#include <iostream>
#include <string>

using namespace std ;

int main()
{
	// ask for and read the student's name
	cout << "Please enter your first name: ";
	string name;
	cin >> name;
	cout << "Hello, " << name << "!" << endl;

	// ask for and read the midterm and final grades
	cout << "Please enter your midterm and final exam grades: ";
	double midterm, final;
	cin >> midterm >> final;

	// ask for the homework grades
	cout << "Enter all your homework grades, "
	        "followed by end-of-file: ";

	// the number and sum of grades read so far
	int count = 0;
	double sum = 0;

	// a variable into which to read
	double x;

	// invariant:
	//     we have read `count' grades so far, and
	//     `sum' is the sum of the first `count' grades
	while (cin >> x)
	{
		++count;
		sum += x;
	}

    while (count == 0 )
    {
        cout <<"You haven't entered any values" << endl;
        cout << endl ;
        cout << "Enter all your homework grades, "
	        "followed by end-of-file: ";
        // invariant:
        //     we have read `count' grades so far, and
        //     `sum' is the sum of the first `count' grades
        while (cin >> x)
        {
            ++count;
            sum += x;
        }
    }

	// write the result
	streamsize prec = cout.precision();
	cout << "Your final grade is " << setprecision(3)
	     << 0.2 * midterm + 0.4 * final + 0.4 * sum / count
	     << setprecision(prec) << endl;

	return 0;
}

As the user don't put in any numbers they get a warning and get a chance to do it again.
But here the warning is displayed without giving the user a moment to do the input again.

Why is this happening and how can I solve this ?

Roelof

Most likely because you have crap left in the input buffer. Clear it out with cin.ignore.

Hoi Elysia.

Something like this :

Code:

 while (count == 0 )
    {
        cin.ingnore (1000, '/n') ; 
        cout <<"You haven't entered any values" << endl;
        cout << endl ;
        cout << "Enter all your homework grades, "
	        "followed by end-of-file: ";
        // invariant:
        //     we have read `count' grades so far, and
        //     `sum' is the sum of the first `count' grades
        while (cin >> x)
        {
            ++count;
            sum += x;
        }

Roelof

You should probably only ignore after something failed ;-). Furthermore, '/n' isn't legal, I think you meant '\n'.

Did you try compiling that?

Yes.

I tried it and I mean '\n'

It compiles but still a infentive loop.
EVOEx : when count == 0 then it fails because nothing has be inputted.

Roelof

Then post your real code, instead of something you typed up full of errors.

oke,

Here the code :

Code:

#include <iomanip>
#include <ios>
#include <iostream>
#include <string>

using namespace std ;

int main()
{
	// ask for and read the student's name
	cout << "Please enter your first name: ";
	string name;
	cin >> name;
	cout << "Hello, " << name << "!" << endl;

	// ask for and read the midterm and final grades
	cout << "Please enter your midterm and final exam grades: ";
	double midterm, final;
	cin >> midterm >> final;

	// ask for the homework grades
	cout << "Enter all your homework grades, "
	        "followed by end-of-file: ";

	// the number and sum of grades read so far
	int count = 0;
	double sum = 0;

	// a variable into which to read
	double x;

	// invariant:
	//     we have read `count' grades so far, and
	//     `sum' is the sum of the first `count' grades
	while (cin >> x)
	{
		++count;
		sum += x;
	}

    while (count == 0 )
    {
        cin.ignore (1000, '\n'); 
        cout <<"You haven't entered any values" << endl;
        cout << endl ;
        cout << "Enter all your homework grades, "
	        "followed by end-of-file: ";
        // invariant:
        //     we have read `count' grades so far, and
        //     `sum' is the sum of the first `count' grades
        while (cin >> x)
        {
            ++count;
            sum += x;
        }
    }

	// write the result
	streamsize prec = cout.precision();
	cout << "Your final grade is " << setprecision(3)
	     << 0.2 * midterm + 0.4 * final + 0.4 * sum / count
	     << setprecision(prec) << endl;

	return 0;
}

Roelof

How about:

Code:

#include <iomanip>
#include <ios>
#include <iostream>
#include <string>

using namespace std ;

int main()
{
	// ask for and read the student's name
	cout << "Please enter your first name: ";
	string name;
	cin >> name;
	cout << "Hello, " << name << "!" << endl;

	// ask for and read the midterm and final grades
	cout << "Please enter your midterm and final exam grades: ";
	double midterm, final;
	cin >> midterm >> final;
        cin.ignore (1000); 

	// ask for the homework grades
	cout << "Enter all your homework grades, "
	        "followed by end-of-file: ";

	// the number and sum of grades read so far
	int count = 0;
	double sum = 0;

	// a variable into which to read
	double x;

	// invariant:
	//     we have read `count' grades so far, and
	//     `sum' is the sum of the first `count' grades
	while (cin >> x)
	{
	        cin.ignore (1000); 
		++count;
		sum += x;
	}

    while (count == 0 )
    {
        cin.ignore (1000); 
        cout <<"You haven't entered any values" << endl;
        cout << endl ;
        cout << "Enter all your homework grades, "
	        "followed by end-of-file: ";
        // invariant:
        //     we have read `count' grades so far, and
        //     `sum' is the sum of the first `count' grades
        while (cin >> x)
        {
	    cin.ignore (1000); 
            ++count;
            sum += x;
        }
    }

	// write the result
	streamsize prec = cout.precision();
	cout << "Your final grade is " << setprecision(3)
	     << 0.2 * midterm + 0.4 * final + 0.4 * sum / count
	     << setprecision(prec) << endl;

	return 0;
}

Does this work?

Hoi Elysia,

It don't work.
Still only the message that there is no input and that the whole time.

Roelof

Edit 1 :

Maybe use a vector to check for input and after no input use a return 1.
The same as the example in the book.

Bah. If no one helps you in the meantime, I'll take a look when I get home.

Oke,

Don't hurry.
I think it will be 2020 when I have the book ready.

Roelof

O_o

Depending on what you want to do, the logic of the code is broken.

In this example, I've shown a possible fix and noted part of the problem.

Soma

Code:

#include <iomanip>
#include <ios>
#include <iostream>
#include <string>

using namespace std ;

int main()
{
	// ask for and read the student's name
	cout << "Please enter your first name: ";
	string name;
	cin >> name;
	cout << "Hello, " << name << "!" << endl;

	// ask for and read the midterm and final grades
	cout << "Please enter your midterm and final exam grades: ";
	double midterm, final;
	cin >> midterm >> final;

	// ask for the homework grades
	cout << "Enter all your homework grades, "
	        "followed by end-of-file: ";

	// the number and sum of grades read so far
	int count = 0;
	double sum = 0;

	// a variable into which to read
	double x;

	// invariant:
	//     we have read `count' grades so far, and
	//     `sum' is the sum of the first `count' grades
	do {
	while (cin >> x)
	{
		++count;
		sum += x;
	}
	if(!cin.eof())
	{
      cin.clear();
      cin.ignore(1000, '\n');
      cout << "not a double value\n";
	}
	} while(!cin.eof());

   // this will not work. the last block runs until EOF
   // EOF is a state that can't logically be ignored
   // or cleared as the next read would just EOF again
    /*while (count == 0 )
    {
        cin.ignore (1000);
        cout <<"You haven't entered any values" << endl;
        cout << endl ;
        cout << "Enter all your homework grades, "
	        "followed by end-of-file: ";
        // invariant:
        //     we have read `count' grades so far, and
        //     `sum' is the sum of the first `count' grades
        while (cin >> x)
        {
	    cin.ignore (1000);
            ++count;
            sum += x;
        }
    }*/

	// write the result
	streamsize prec = cout.precision();
	cout << "Your final grade is " << setprecision(3)
	     << 0.2 * midterm + 0.4 * final + 0.4 * sum / count
	     << setprecision(prec) << endl;

	return 0;
}

Oke,

I understand but not complety.
But why not cin .eof() when displaying the error message
Must that be cin.eof.
And if a user enters one value then it's good and the user may use EOF otherwise the loop will run forever.

Roelof

Edit 1 : I tried it and it's not working. When you now use a EOF then the programm does not respond anymore

I got it working with this:

Code:

#include <iomanip>
#include <ios>
#include <iostream>
#include <string>

using namespace std ;

int main()
{
	// ask for and read the student's name
	cout << "Please enter your first name: ";
	string name;
	cin >> name;
	cout << "Hello, " << name << "!" << endl;

	// ask for and read the midterm and final grades
	cout << "Please enter your midterm and final exam grades: ";
	double midterm, final;
	cin >> midterm >> final;

	// the number and sum of grades read so far
	int count = 0;
	double sum = 0;

	// a variable into which to read
	double x;

	// invariant:
	//     we have read `count' grades so far, and
	//     `sum' is the sum of the first `count' grades
	while (count == 0 )
	{
		// ask for the homework grades
		cout << "Enter all your homework grades, "
			"followed by -1: ";
		for (;;)
		{
			cin >> x;
			if (x == -1)
				break;
			++count;
			sum += x;
		}
		if (count == 0)
		{
			cout <<"You haven't entered any values" << endl;
			cout << endl ;
		}
	}

	// write the result
	streamsize prec = cout.precision();
	cout << "Your final grade is " << setprecision(3)
		<< 0.2 * midterm + 0.4 * final + 0.4 * sum / count
		<< setprecision(prec) << endl;

	return 0;
}