Need Programming Homework Help Now!

[hapoo]

ok guys... simple program but i dont have time. I just need a program writen in C that calculates the factorial of a number!


kinda like this


main()
{
int num;
scanf("%d", &num);
factorial(num);
printf("%d", num);
}


int factorial(int num)
{
int total;
if(num = 1){return 1;}
total = num*factorial(num-1);
return total;
}


The program is due tonight, any and all help is greatly appreciated! Thanks in advance.

[Markel]

Although factorial calculation is the classic example used for recursion, it is actually a very poor implementation due to the calculation intensity once numbers get very large. Most efficient implementations use a lookup table for smaller numbers (the last time I remember this was like up to 27 or something, but that was a few years ago), and then use a logarithmic function to estimate values that are above this (since the number of significant digits that can be used can be returned by such a function).

However, as long as you have a properly recursive compiler, your example looks like it should work.

[hapoo]

The program MUST be recursively excecuted and it MUST check for overflow... which btw happens after 13 factorial on a 32 bit computer.
the one i just wrote returns 1 for any number... and doesn't check for overflow.

[Markel]

One note - if you can use a long instead of an int, you won't overflow as quickly.

[hapoo]

Originally posted by Markel
One note - if you can use a long instead of an int, you won't overflow as quickly.


must use integer. Just following instructions on the lab, not making this stuff up :)

[Markel]

Can you just put a check in factorial for num > 13 (print error and return 0 or something)?

[hapoo]

Originally posted by Markel
Can you just put a check in factorial for num > 13 (print error and return 0 or something)?

Short answer no
long answer:
And i quote: "Since C is a portable language the factorial program should be able to run on ANY machine and hence should find overflow in ANY machine."

[Markel]

Ah, I'm beginning to get a better idea what's up. Hmm -- perhaps you could do something with MAXINT that would help.

[hapoo]

whats maxint?

[Markel]

In most C implementations that I have seen MAXINT is a pre-defined constant equal to the largest positive integer value.