Floating Point isalpha();

Can isalpha() check floating point variables, here is my code.

Code:

#include <iostream.h>
#include <conio.h>
#include <stdlib.h>
#include <string.h>
#include <ctype.h>



int main(void)

{

	//Declare the variables
	float cost, quant, price, vat, full, temp;
	int length, count;
	char yesno, vats[10];

		  while (yesno != 'n' && yesno != 'N')
		  {
				//Get info from user
				clrscr();
				gotoxy(20, 12);

				cout<<"Please enter the price of the product: ";
				cin>>cost;

				if (isalpha(cost))
				{
					 cout<<"Thats Wrong";
				}

				clrscr();
				gotoxy(20, 12);

				cout<<"Please enter the quantity of products: ";
				cin>>quant;

				if (isalpha(quant))
				{
					 cout<<"Thats Wrong";
				}

				clrscr();
				gotoxy(20, 12);

				cout<<"Please enter your rate of vat: ";
				cin.ignore();
				cin.getline(vats, 10);

				length=strlen(vats);

				if (length == 0)
				{
					 temp = 17.5;
				}

				else
				{
					 temp=atof(vats);
				}


				//do the calculation
				temp= temp / 100;
				price= cost * quant;
				vat= cost * quant * temp;
				full= price + vat;

				clrscr();
				gotoxy(20, 12);

				//give the answer
				cout<<"The price of "<<quant<<" product(s) at "<<cost<<" each = £"<<price;

				gotoxy(20, 14);

				cout<<"The vat at "<<temp*100<<"% = £"<<vat;

				gotoxy(20, 16);

				cout<<"Price plus vat = £"<<full;

				gotoxy(20, 19);

				cout<<"Would you like to use the program again? ";
				cin>>yesno;
				cout<<"\n";

		  }
		  clrscr();
		  gotoxy(20, 12);

		  cout<<"Thankyou Bye!";

		  for (count=0; count<=20000; count++)
		  {
				for (int j=0; j<=15000; j++)
				{
				}
		  }

return 0;
}

don't worry about the for loop at the end and all that its only the isalpha I'm having trouble with.

I thought isalpha() was used to check for characters and not digits. Isn't isdigit() what you want?

You have to read them as strings if you want to use that function. Check all the characters in the string including one dot. Or use cin.fail() to determine if assignment to float succeeded...

There is a function called atof that will return a floating point number from a string agrument. This should help you hopefully.

Code:

#include <iostream.h>

int main(void)
{
  const int MAX_BUFFER=512;

  double Converted=0;
  char Buffer[MAX_BUFFER];

  cout << "Please enter a floating point number: ";
  cin.get(Buffer, sizeof Buffer);

  Converted=atof(Buffer);

  cout << "\n\nThe value of double is: " << Converted;
  getchar();

  return 0;
}

Code:

$man atof

ATOF(3)             Linux Programmer's
Manual             ATOF(3)

NAME
       atof - convert a string to a double.

SYNOPSIS
       #include <stdlib.h>

       double atof(const char *nptr);

DESCRIPTION
       The  atof()  function  converts the initial portion of the
       string pointed to by nptr to double.  The behaviour is the
       same as

              strtod(nptr, (char **)NULL);

       except that atof() does not detect errors.

atof does not check if input is invalid, so that should be remembered.

What you're looking for is something like this:

Code:

cin >> value; 
       
while (cin.fail())
{ 
           cin.clear(); 
           cin.ignore(0xFF,'\n');
           cout << "An error has occoured! Please re-enter your value: ";
           cin >> value;
}

Code you explain what "cin.ignore(0xFF,'\n');" does by any chance, thanks.

istream& ignore (streamsize n = 1, int delim = EOF );
Extract and discard characters.
Extracts characters from input stream and discards them.
Extraction ends when n characters have been discarded or when delim is found, whichever comes first. In this last case delim is also extracted.

Parameters:

n
Maximum number of characters to be extracted and ignored.
This is an integer value of type streamsize
delim
Delimiter character.

Return Value:

The function returns *this

Example:

Code:

// istream ignore
#include <iostream>
using namespace std;

int main () 
{
    char first, last;

    cout << "Enter your first and last names: ";
 
    first=cin.get();
    cin.ignore(256,' ');

    last=cin.get();

    cout << "Your initials are " << first << last;

    return 0;
}

This example shows the use of ignore to ignore input characters until a whitespace is found.