long long?

[Daniel Samper]

Hi all ..
I'm trying to do this:

1111 x 1111 = 1234321

11111 x 11111 = 123454321

111111 x 111111 = 12345654321

1111111 x 1111111 = 1234567654321

11111111 x 11111111 = 123456787654321

111111111 x 111111111=12345678987654321

I wrote this code:

#include <stdio.h>

int i;
long long int product;
int factor;

int main(){
    factor = factor * 10 + 1;
    for(i=0;i<8;i++){
        factor = factor * 10 + 1;
        product = factor * factor;
        printf("%d x %d = %lld \n",factor, factor, product);
    }    

        
}

But I get this:


11 x 11 = 121
111 x 111 = 12321
1111 x 1111 = 1234321
11111 x 11111 = 123454321
111111 x 111111 = -539247567
1111111 x 1111111 = 1912040369
11111111 x 11111111 = -2047269199
111111111 x 111111111 = 1653732529

Some help please? Thanks. :-)

[programmer1]

Hi, I am new at C. But I wanna help. I got what you want. But in a "not useful" way. Sorry for this, I hope the experts() will help you but that is my solution.

#include <stdio.h>
 
int i;
long int product;
int factor;
 
int main(){
    factor = factor * 10 + 1;
factor = factor * 10 + 1;
factor = factor * 10 + 1;
    for(i=0;i<6;i++){
        factor = factor * 10 + 1;
        product = factor * factor;
        printf("%d x %d = %lld \n",factor, factor, product);
    }    
 
         
}

[grumpy]

Change the type of factor to be long long, not int.

[Daniel Samper]

I wrote this:

#include <stdio.h>

int i;
long long product;
int factor;

int main(){
    factor = factor * 10 + 1;
    for(i=0;i<8;i++){
        factor = factor * 10 + 1;
        product = factor * factor;
        printf("%d x %d = %lld \n",factor, factor, product);
    }    

        
}

but I get the same screen ...

[jimblumberg]

Both factor and product must be either unsigned long long or long long.

Jim

[dan_paul]

Here is an article about numeric types in C that might help you:

http://www.exforsys.com/tutorials/c-language/c-programming-language-data-types.html

You may want to try an unsigned long long int if you're confident that your integers will always be positive.

As the tutorial explains, the size that you are actually allocated for numeric types is system dependent (although certain minimum values are guaranteed by the C standard). So, if you're pushing the upper limits of your type, you won't be guaranteed that it will work on all systems.

If you want an arbitrarily large number and only need addition and multiplication, it might be interesting to write a function for adding and multiplying integers represented as strings. Maybe not this simplest solution but it could definitely be done and would free you from any built in size limitations.

[Daniel Samper]

Thank you very much.

[FloridaJo]

Beware of that page, there is a bunch of errors. Sloppy code.
See my comment on that page.