Anyone who is good at C++

tigerwoods99

Aight, I am tryin to write this program but I don't know how to do it without sub strings.



"Your program is required to prompt for an 8-digit credit card number as ONE integer, not as a string object, or 8 single-digit integer"



1) Sum up digit 1, 2, 3, 6, 7, 8.

2) Multiply the sum by 3 and increase the product by 1.

3) If the result is over 100 only keep the lower two digits.

4) These two digits should be the correct middle two-digits



Write a loop to repeat the whole task until a correct CCNO is entered, or any other additional features you like to add that will add dimensions to this very simple program.





I'm just starting out on this, so I don't really know much on C++.



[ 10-17-2002: Message edited by: TigerWoods99 ]</p>

jutus

The trick is to use mod. mod is the operation that gives you the remainder after division.



e.g. 13 mod 10 = 3



so say you have a credit card number as an int: 12345678

(12 million, 345 thousand, blah blah)



Let's say you want the third digit from left.



12345678 mod 10000000 = 2345678

2345678 mod 1000000 = 345678



345678 div 100000 = 3 (truncate)



3 is the third digit.



that's one way to do it.



The rest of your problem looks pretty easy if you use the above method to extract the nth digit.



good luck,



-j

airsluf

tigerwoods99

I'm still stuck.



Like, can I just use an if statement to tell the cpu how to get the middle digits or what? And can I do something like 'isValidCard' etc?

ast3r3x

weird, we are doing something almost exactly like this





...getting ready for the national programming thing? question from previous yr?



[ 10-17-2002: Message edited by: ast3r3x ]</p>

airsluf

tigerwoods99

Nope.



Alright so I've got this:



#include &lt;iostream&gt;

#include &lt;string&gt;



using namespace std;



int main(void)

{



int FirstDigit, SecondDigit, ThirdDigit, FourthDigit, FifthDigit, SixthDigit, SeventhDigit, EighthDigit



cout&lt;&lt;"Please enter credit card number \\\

"endl;



cin&gt;&gt;num;



int Sum=FirstDigit + SecondDigit + etc.



so I can define the sum first, then get the multiple of 3, then get that, then get it w/out 100s using the mod.



Now what?

tigerwoods99

Can someone IM me or something...supermacG9

madmax559

heres a hint,...



instead of using so many variables

use an array...



as the problem states you cant use a string

so dont use one

you can accept keyboard input & assign each

key into an array



something like

while (ch != '0x13')

{

a[i] = getche();

}



from then on its a piece of cake

also look at the stl classes if you dont

want to use an array

in which case a simple list would do the trick

madmax559

addon to my post above



&gt;Write a loop to repeat the whole task until a &gt;correct CCNO is entered,



um thats a simple mod 10 checksum

google is your buddy

tigerwoods99

Can you IM me please and tell me more about the array?

airsluf

amorph

What is getche()?! I don't recall that from the Standard Library. If it's a compiler-specific extension, it has no place in a general C++ assignment.



The most fundamental problem you have, TW, is sketching out the program organization before you write a single line of code. Your followup question makes that clear. You should talk to your teacher about that. You should be able to sketch out the structure of the code first, using boxes and arrows and/or pseudocode and/or whatever strikes your fancy, and fire up the compiler when you actually have a design to work from.



The basic rule of thumb I use is to break a program down into a list of tasks. Anything that would take more than a handful of lines, or that has to be done more than once, ends up in a function (or method).



You can also break the problem down into smaller problems, and solve them one at a time. For instance, write a program that reads in an eight digit integer and prints out "You entered &lt;whatever you entered&gt;." When you've got it working, add something that tells you what the 5th digit of the number is, and so forth. Then you can test each part individually, and assemble your solution incrementally instead of trying to do everything at once.



[ 10-18-2002: Message edited by: Amorph ]</p>

ast3r3x

[code] void numcruncher()

{

int digit1,digit2,digit3,digit4,digit5,digit6,digit,di git8,ccnum,sum;

cout&lt;&lt;"Input 8 digit Credit Card Number: "&lt;&lt;endl;

cin&gt;&gt;ccnum;



if(ccnum&gt;9999999 && ccnum&lt;100000000)

{

digit1=ccnum/10000000;

digit2=(ccnum%10000000)/1000000;

digit3=((ccnum%10000000)%1000000)/100000;

digit4=(((ccnum%10000000)%1000000)%100000)/10000;

digit5=((((ccnum%10000000)%1000000)%100000)%10000)/1000;

digit6=(((((ccnum%10000000)%1000000)%100000)%10000 )%1000)/100;

digit7=((((((ccnum%10000000)%1000000)%100000)%1000 0)%1000)%100)/10;

digit8=((((((ccnum%10000000)%1000000)%100000)%1000 0)%1000)%100)%10;



sum=digit1+digit2+digit3+digit6+digit7+digit8;

sum=(sum*3)+1;

if(sum&gt;=100)

{

sum-100

}

else

{

sum=sum

}



cout&lt;&lt;sum&lt;&lt;endl;



}

else

{

numcruncher();

}

}



void main()

{

numcruncher();

getch();

return0:

} </pre><hr></blockquote>



sorry i just did thta in textedit, no debugger or anything to test, so i'm sure there are some errors





just to let people knwo i did this in like 10min, so the code is a little crude and could be optimized...specially the way i got all the digits, because we did something like thi at school and there was a way that was alot easier and alot less code.



[ 10-18-2002: Message edited by: ast3r3x ]</p>

tigerwoods99

That program lookks to be checking for 8 digitsso if I did something like the sum of all numbers, multiply by 3, add 1, w/out hundreds etc. and then use something like if ' ' whatever to define it. Then if it they don't match up it will give you an invalid message. Does this sound like it would work?



Something like:



Sum = digit1 + digit2 + digit3 etc...



then something for the middle 2 digits



I could do mod for all of them to get the nth digit however wouldn't that just be writing a lot?



Not trying to get you to do it really, I'm trying to understand everyone's posts. Thanks.

tigerwoods99

[quote]Originally posted by madmax559:

<strong>heres a hint,...



instead of using so many variables

use an array...



as the problem states you cant use a string

so dont use one

you can accept keyboard input & assign each

key into an array



something like

while (ch != '0x13')

{

a[i] = getche();

}



from then on its a piece of cake

also look at the stl classes if you dont

want to use an array

in which case a simple list would do the trick</strong><hr></blockquote>



So basically for that while statement you'd be getting the 13th number there?



What I don't understand is the 'getche()'

dogcow

getche(); captures the keystroke entered. I remember using this with Turbo C++ for DOS. I really don't know if its a standard command or just for that compiler.

tigerwoods99

Thanks man.



I just figured out I can do a for to make a loop in the program so what I did is



for (int lcv=0; lcv&lt;=8; lcv++)

{