Why the output of my program is "0" when I multiply large numbers like 256 and 8192 i

Hi. Could someone help me. I am making a C language program that will display the product of any large number, but I a getting 0 instead! Here is a sample program that I made...

Source code:

Code:

#include<stdio.h>
#include<conio.h>
int main();
{
long long int a=256;
long long int b=8192;
long long int ans=a*b;
printf("%d",ans);
getch();
return 0;
}

Output: 0

We all know that 256 x 8192 = 2097152, but why the computer is still displays "0"? I tried changing ans to double, but still it is "0". What will I do?

PS. If you will make a program modifying it, please make it as simple as possible. Thanks.

Well you need to look up the correct format letter(s) for printing a long long.

If you're using a port of MinGW (dev-c++, code::blocks) then you need to check how to use printf on the MSDN site.

Originally Posted by Salem

Well you need to look up the correct format letter(s) for printing a long long.

If you're using a port of MinGW (dev-c++, code::blocks) then you need to check how to use printf on the MSDN site.

So how can I display the right value? By the way, I am using the Turbo C in DOS.

Originally Posted by Nagasaki

So how can I display the right value? By the way, I am using the Turbo C in DOS.

Salem will be DELIGHTED to hear that! < rofl >

Have you tried using %lld as the printf format?

The right format is right there in your help for printf().

There are limits to the size of any data type. You may want to look up your system's values. They can be found in limits.h and ctype.h, both (in my version of Turbo C).

Does TurbidCrap even have long long?

Get a real compiler.
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ok, I got it. All I need is change %d to %ld. I just want to ask something. If %ld can display a 7-digit number, How I can print a 11-digit number?

Turbo C was set to the AT&T standard, in it's earliest versions, and had only unsigned long int as it's highest integral data type. I'm not sure what the later versions of Turbo C had.

For a larger number, you could:

1) Check out limits.h and see what your largest double is. Use the double if it's big enough, and then round off the double, and print only the part to the left of the decimal point.

2) Use an array of digits (char or int), to hold your big int's. You'll have to write up your own functions to handle addition, subtraction, multiplication and division, and anything else you want. Not too bad for the basics, but if you want higher math functions, use #3.

3) Get a large number library. GNU has one that's well known. Laserlight linked to it just last week, here.

Using an unsigned int will effectively double the range of your positive int's, but eleven digits is a reach.

Oh. That's a big help. I am actually using this sample program as a reference to my real program. Our professor wants us to make a program that will output this using the function call.
1 2 2 4 8 32 256 8192 2097152 17179869184
I have made a program, but as of now, I got the 1st to the 9th element, my problem is on the 10th and last element. Can a 2-dimensional long array do it?

Originally Posted by Nagasaki

So how can I display the right value? By the way, I am using the Turbo C in DOS.

Fred Flintstone will be so proud!

1) Get a better compiler... that one is at least 20 years out of date.

2) Get a better operating system ... nobody has actualy used MS-DOS in over a decade.

3) Get a better school ... any school still teaching Turbo C or DOS is so behind the times your career is doomed to failure before it even starts.

4) Click the red link in my .sig (bottom of this message)... read and believe!

Pelles C <-- 32 and 64 bit compilers, full windows header and lib set, full set of resource editors, best help file available ... and it's free.

So you may be able to use the #1 technique then. That would be a lot easier than anything else.

To make it work declare your variables as doubles, and do the exponentiation of 2, as you need to (21 times I believe). Your answer might be OK, because it's a power of 2. If it needs to be rounded, add 0.5 to it and then divide by 1, to round it off.

Give that a shot.

I'm getting that sneaky feeling that there is a bit based, power of 2, super easy answer to this, but I don't know it. Did your prof mention something like this, and like to be "sneaky"?

Originally Posted by Adak

I'm getting that sneaky feeling that there is a bit based, power of 2, super easy answer to this, but I don't know it.

Well, you could add powers (and end up with the Fibonacci sequence) and then use a left shift, but keeping track of the last two numbers generated would work just as well.

The problem with 256 * 8192 is that it's too big for a 16 bit integer and since it is powers of 2, the result left in the lower 16 bits is all 0s.

Do yourself a favor...

Code:

#include <stdio.h>

int main (void)
 { 
    printf("%d\n", sizeof (int));
    printf("%d\n", sizeof (long int));
    printf("%d\n", sizeof (long long int));
    return 0;
  }

If your answers are 2 4 4 instead of 4 4 8 .... you need a new compiler.

The biggest number you're going to put into 2 bytes is 65,535
The biggest number for 4 bytes is 4,294,967,295
The bittest number for 8 bytes is 18,446,744,073,709,551,614

Can you see why a new compiler might be a good idea?

I didn't ask him how he was finding the next number in the sequence. He said he's finding them, so I took that to mean he had the math logic working OK.

I would say it's a bit odd that all the numbers are powers of two, but then CommonTater or Andrew would just point out that no, it was EVEN - so I won't.

Originally Posted by Adak

I would say it's a bit odd that all the numbers are powers of two

Only if you don't notice what the pattern actually is. But yes, bit shifting is only going to work if he's got 21 bits there for him to shift into; shifting a 1 off the edge of the register and down to the bottom of the computer case doesn't help.

Originally Posted by tabstop

Only if you don't notice what the pattern actually is. But yes, bit shifting is only going to work if he's got 21 bits there for him to shift into; shifting a 1 off the edge of the register and down to the bottom of the computer case doesn't help.

Oh WOW... after all these years... I finally know where all that dust in my computer cases comes from!

THANK YOU!

LOL...