!isdigit woes!!

[bkapitan]

I'm trying to write a for loop that removes all the letters from a string. When I run it, it seems like the !isdigit function only removes a handful of letters, leaving some. Is there an easier way to do this? Thanks in advance for the help!!

#include "stdafx.h"
#include <cctype>
#include <sstream>
#include <iostream>
#include <string>

#define ISBN_X 9
#define ISBN_SIZE 10

using namespace std;

bool is_ISBN10_Valid(string);

int _tmain(int argc, _TCHAR* argv[])
{
	string c;
	int a;
    string isbnNo; 		
	cout<< "Please enter your 10 digit ISBN now:  "; //here the user enters his or her input.
    
	std::getline(std::cin, isbnNo);////here the user enters his or her input, whitespaces and all.	
	cout << "Length of text input: " << isbnNo.length() << endl << endl << endl; // Displayes the total number of input characters.
	
     	
	//Below is a for loop which should remove all the numbers from the input string.
	for ( int x = 0 ; x <= isbnNo.length() ; x++)
		{        
			if (!isdigit(isbnNo[x]))			// If the input character is not a number....               
			    isbnNo.erase(x, 1);				 //...then remove it from our string.					
		
		}

[guestgulkan]

If you erase a character you should not do x++, because the string has closed up the gap caused by erasing the char.

Try this:

for ( int x = 0 ; x <= isbnNo.length() ; )
{        
        if (!isdigit(isbnNo[x]))	// If the input character is not a number....               
             isbnNo.erase(x, 1);	 //...then remove it from our string.
        else
             x++;				
}

[bkapitan]

guestgulkan, thanks so much! This works very well. However, it seems to skip over letters and erases every other one. Any idea what the problem is?

[guestgulkan]

This is what I have - NOTE that there is a correction in the loop test,
it is now x < isbnNo.length()

For the tests that I did it worked ok.

#include "stdafx.h"
#include <cctype>
#include <sstream>
#include <iostream>
#include <string>

#define ISBN_X 9
#define ISBN_SIZE 10

using namespace std;

bool is_ISBN10_Valid(string);

int _tmain(int argc, _TCHAR* argv[])
{
	string c;
	int a;
    string isbnNo; 		
	cout<< "Please enter your 10 digit ISBN now:  "; //here the user enters his or her input.
    
	std::getline(std::cin, isbnNo);////here the user enters his or her input, whitespaces and all.	
	cout << "Length of text input: " << isbnNo.length() << endl << endl << endl; // Displayes the total number of input characters.
	
     	
	//Below is a for loop which should remove all the numbers from the input string.
    for ( int x = 0 ; x < isbnNo.length() ; ) //*** Correction made to the loop test 
    {        
        if (!isdigit(isbnNo[x]))	// If the input character is not a number....               
            isbnNo.erase(x, 1);	 //...then remove it from our string.
        else
            x++;				
    }

}