Validate data on input

Hi folks,

Nice to be on this forum.

I'm kinda new to C++ and have been working my way through a few on-line tutorials and have bought myself an idiots guide book but have come to a halt with my little program !

I've got a car database program that I've been working on and it was working fine until i decided to do a spot of validation on entry. When a user inputs a car registration number I want it only to be able to take 5 charcters and if it is any more or any less, to print a error message to the screen and then give the oppertunity to input the registration number again. What's the best way to go about this ? I tried a few things but the keep coming back with errors !

Any help on this to point me in the right direction would be much appreciated !

H_M

You can do something like this:

Code:

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

int main()
{
	
	string input;
	bool goodInput;
	
	do
	{
		goodInput = true;
		
		cout<<"Enter exactly 5 characters: ";
		getline(cin, input);
		
		if(input.length() != 5)
		{
			cout<<"Idiot!"<<endl;
			goodInput = false;
		}

	}while(goodInput == false);
	
	return 0;
}

....or this:

Code:

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

int main()
{
	
	string input;
		
	while(true)  //infinite loop
	{
		cout<<"Enter exactly 5 characters: ";
		getline(cin, input);
		
		if(input.length() != 5)
		{
			cout<<"Idiot!"<<endl;
		}
		else
		{
			break;
		}
	}
	
	return 0;
}

7stud, thank you for such a speedy reply - much appreciated !

I decided on using your second post as a guide, as that looked like the easiest for me to use, and I amended it slightly to fit my little program, but, i still can't get it to work ! It still allows me to enter less than or more than 5 characters ! This is my little part that i am having trouble with:

Code:

// Create a new car record in the database
void add_car(car_type cars[])
{
	int no_of_cars, next_record_no;
	int length;
	length = 5;
 
	// Display heading
	clear_screen();
	cout << "                          ADD A CAR"
		 << endl << endl << endl;

	// Count how many cars are already in the database
	no_of_cars = car_count(cars);

	// Report to user
	cout << endl << "There are " << no_of_cars << " cars in CarBase."
		 << endl;

	// Set the record number at which to add the new car
	next_record_no = no_of_cars;

	// If database is not full, add a car
	if (no_of_cars < MAX_CARS)
	{
	    cout << endl << "Make:    " << flush;
		gets(cars[next_record_no].make);
		cout << "Model:   " << flush;
		gets(cars[next_record_no].model);

		//Do data Validation for registration number
				
		while(true)
		{
			cout << "Reg No:  " << flush;
			gets(cars[next_record_no].regno);

		if((cars[next_record_no].regno, length) != 5)
		{
			cout<<"The registration number must equal 5 characters. Please enter it again. " << endl;
		}
		else
		{
			break;
		}
		
	}

		cout << "Year:    ";
		cin  >> cars[next_record_no].year;
		cout << "Price:   ";
		cin  >> cars[next_record_no].price;
		cout << "Mileage: ";
		cin  >> cars[next_record_no].mileage;
		cout << "Engine size in cc:   ";
		cin  >> cars[next_record_no].engine;
	}
	// If database is full, give message
	else
	{
		cout << "No room for any more cars\a" << endl;
	}
 
	// Database has changed so save it
	save_data(cars);
}

Can you see where I have went wrong !? It's where it starts with the comments "//Do data Validation for registration number". Just thought I would post all the code that I have for that prototype incase it helps ? Once I manage to get the registration number one working, I am going to do the rest, hopefully !

Any pushes in the right direction would be greatly appreciated !

H_M

Code:

if((cars[next_record_no].regno, length) != 5)

Compare that to my if statement.

Also, what type is regno? If it's not a string type, it doesn't have a length() method. If it's a char array, you have to use strlen() to get the length.

Hi 7stud,

Once again, thank you very much for your reply and help on this.

I've changed it a bit now and have been using strlen and, I can get the error message to appear, but, it doesn't matter how many chars I enter whether it is more or less than 5, it still appears ! This is driving me crazy ! Any ideas on why it won't go on to ask for the Year when 5 chars are enterted ? I'm sure i'm missing something but can't think what.

Code:

//Do data Validation for registration number
				
		while(true)
		{
			cout << "Reg No:  " << flush;
			gets(cars[next_record_no].regno);

		if ((cars[next_record_no].regno, strlen) != 5)
		{
			cout<<"The registration number must equal 5 characters. Please enter it again. " << endl;
		}
		else 
		{
			break;
		}
		
		}

Thanks

H_M

Hi,

Let's recap a little. I posted an if statement like this:

Code:

if(input.length() != 5)

which you essentially applied like this:

Code:

if( (regno, length) != 5)

Do you see any difference? C++ has very strict syntax, and you can't just add a comma and leave out the period and put the parentheses in a different location. Your next attempt was essentially:

Code:

if ( (regno, strlen)) != 5)

in which you just propogated the mistakes from before, and added some new ones because the strlen() function is used differently than the length() function--look it up here:

http://www.cppreference.com/

Hi 7stud,

Again, thanks for all your help with this ! I'm still having the same problem trying to get the strlen() function to work with my program, but think I will get there in the end, hopefully !

H_M

I'm still having the same problem trying to get the strlen() function to work with my program, but think I will get there in the end, hopefully !

Write a practice program that has two lines:

1) declare and initialize a char array

2) display the length of the string using strlen()

Originally Posted by 7stud

You can do something like this:

Code:

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

int main()
{
	
	string input;
	bool goodInput;
	
	do
	{
		goodInput = true;
		
		cout<<"Enter exactly 5 characters: ";
		getline(cin, input);
		
		if(input.length() != 5)
		{
			cout<<"Idiot!"<<endl;
			goodInput = false;
		}

	}while(goodInput == false);
	
	return 0;
}

Slight nit-picky change. Rather than change goodInput all the time you could use:

Code:

goodInput = false;
do
{
    cout << "Enter exactly 5 characters: ";
    getline(cin, input);
    if (input.length() != 5)
    {
        cout << "Idiot!" << endl;
    }
    else
    {
        goodInput = true;
    }
}while (goodInput == false);

And using a while you don't need an infinte loop with break:

Code:

goodInput = false;
while (goodInput == false)
{
    cout << "Enter exactly 5 characters: ";
    getline(cin, input);
    if (input.length() != 5)
    {
        cout << "Idiot!" << endl;
    }
    else
    {
        goodInput = true;
    }
}

And SPACEs help readability. Told you they were nit-picky...

Hi guys,

Just want to say thanks for all your help with this. I started again using the examples on here, done a couple of tweaks to make it suit my own program and it is working fine ! Even have the strlen() working for all the other inputs now which is great !!

Now, onto another part, making sure duplicates aren't accepted ! If I get stuck, I'll be back !

Thanks again guys, this has to be the no1 C++ forums on the net !

H_M