Validating data Input

I was just wondering on how to validate data in visual c++ (creating a calculator where user type the two numbers in two different text boxes). I know how to do it in c++ but it seems a bit more difficult in GUI. At the moment, i'm reading a input from a text box and converting the string into a int.

I don't have the code here at the moment, as I am at uni at the moment and quickly typing this before I attend one of my lectures.

Basically, i want to be able to test the data is digit, (i was doing some research, but somehow isdigit() doesn't work) and within the int range.. ie. 2.2e-300 to 2.2e303...I'll probably post my code tonite when i get home to show what i have done so far.

One thing, in my 1'st project, which was done in c++, u guys know why when i did after assinging just say 2.2e400, and when i test to see if it is within range i.e if(int < 2.2e-300 || int > 2.2e300), i put up a message. but somehow it doesn't work? i'll provide the code tonite as i said.

Thanks, gotta go...

Code:

bool ValidDigit(char Digit)
{
  if(Digit == '.') return true;
  if((Digit >= '0') && (Digit <= '9')) return true;

  return false;
}

bool ValidNumber(const std::string& Input)
{
  std::stringstream Stream(Input);
  double Value;

  for(int i = 0; i < Input.size(); i++)
  {
    if(!ValidDigit(Input[i])) return false;
  }

  Stream >> Value;

  return (Value >= 2.2e-300) && (Value <= 2.2e303);
}

> bool ValidNumber(const std::string& Input)
Except "123.456.789" would be regarded as valid.

Try using strtod(), check errno to see if there was a conversion error, and check endptr to see if it got to the end of the number properly.

Here's an example of using strtod(). It seems to work for values from 1e-300 to 1e300. I goes a little freaky if I input 1e1000000000 or something similarly small, but that's probably because I don't know how to handle HUGE_VAL or use errno, etc.

Code:

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

const int MAX = 1000;

int main()
{
  char input[MAX]; 
  char *p;
  double result;
  bool invalid = true;
  while(invalid)
  {
	cout << "Please enter a number : ";
	cin >> input;
  
	result = strtod(input, &p); 
	
	 //if user pushed the enter key before other input, input is invalid
	 //if value of p is newline char or null char then all char entered by user were valid.  
	 if(input[0] != '\n' && (*p == '\n' || *p == '\0'))
	{
	  cout << result <<  " is valid input" << endl;
	  invalid = false;
	}	 
	else
	  cout << "Invalid input." << endl;
  }	
	  
  cout << endl;
  char ch;
  cin >> ch; 
  return 0;
}

Note: I assume you know that if the input in the GUI isn't in the form of a Cstyle string, you will need to convert it to a C style string in order to use strtod().

if i have done my research properly, isidigit() only does one character....how would u do it if someone typed 842390jej, and this is converted to integer...how do u check that? i was trying with a for loop but i don't think it works properl, cos u can't do it as not array? sorri i'm only a beginner

Code:

char input[] = "842390jej";
char *endp;
long int res = strtol( input, &endp, 10 );

If all is well, you would expect *endp to be either a space or a '\0'
In this case, *endp would be 'j'.
Whether this is an error as far as you're concerned is up to you.