Member Avatar for BlackHawck

Look at this program compiled using Turbo c++ 3.0 compiler
Aim is to calculate the factorial of a no.

#include<iostream.h>
#include<conio.h>
long double factorial(int);

void main() //main function
{
int inp;
clrscr();
cout<<"Enter a positive no. ";
cin>>inp;
cout<<"factorial is :"<<factorial(inp);//displays factorial
getch();
}

long double factorial(int a)
{
long double fact=1;
while(!a==0)
	{
	fact=a*fact;
	--a;
	}
return fact;
}

But when it runs it gives unexpected result, it can't find the factorial of no. grater than six.

Can you correct this program and explain why it is wrong without altering it's simplicity.....

Remember this program is from a beginner level program so, only correct it , don't use complex methods.

Edited by Narue because: added code tags
  • 5 Contributors
  • 6 Replies
  • 789 Views
  • 12 Hours Discussion Span
  • Latest Post Latest Post by Anuradha Mandal

Dani AI

Generated

Quick diagnosis and a minimal fix.

The expression while(!a==0) is legal C++ but misleading: the unary ! is applied first, so it is evaluated as (!a) == 0, which is true whenever a != 0. That makes the loop work, but it is hard to read and easy to misinterpret. Also prefer int main() instead of void main() in standard C++. Below is a simple, beginner-friendly correction that keeps the original style for Turbo C++:

#include <iostream.h>
#include <conio.h>

long double factorial(int n)
{
    long double fact = 1.0L;
    while (n > 1) {
        fact *= n;
        --n;
    }
    return fact;
}

int main()
{
    int inp;
    clrscr();
    cout << "Enter a positive no. ";
    cin >> inp;
    if (inp < 0)
        cout << "Factorial not defined for negative numbers.";
    else
        cout << "factorial is :" << factorial(inp);
    getch();
    return 0;
}

Notes and troubleshooting:

  • The original loop condition is better written as while (a != 0) or while (a > 0) for clarity. This change alone usually fixes reader confusion (and matches 's suggestion about modern practice).
  • Unexpected results for somewhat small inputs are more often caused by numeric overflow than by the loop; factorials grow very fast (as pointed out). Fixed-width types will overflow at modest n on many compilers—handling arbitrarily large factorials requires a big-integer approach or a library (more advanced).
  • clrscr()/getch() are Borland/Turbo-specific and fine for the school environment. Printing intermediate values or running the same code on a modern compiler quickly distinguishes logic errors from environment/overflow issues (as noted by ).

Recommended Answers

All 6 Replies

Member Avatar for Narue

compiled using Turbo c++ 3.0 compiler

Have you considered dropping that ancient piece of shit and switching to a compiler that isn't twenty years old and severely limited under modern architectures?

it can't find the factorial of no. grater than six

If this were true I would be confused, but your algorithm is correct and works for values of N greater than six. However, factorials grow at an insane rate, and despite using long double to counteract that growth, you're still going to exceed limits (thus invoking undefined behavior) very quickly.

If you want arbitrarily large factorials, you need some kind of big number library such as GMP.

Member Avatar for BlackHawck

I have to use Turbo C++ due to our school syllabus.

And isn't any other method for doing this like use of arrays etc. without using no. lib.?

Thanks!

Member Avatar for Narue

I have to use Turbo C++ due to our school syllabus.

I don't care. If you have to use it, you have to use it, but people are still going to complain that you're learning how to use an environment that's utterly useless outside of your school.

And isn't any other method for doing this like use of arrays etc. without using no. lib.?

You specifically rejected complex methods. Use of arrays constitutes duplicating the effort of an arbitrary length math library, which falls under "complex methods" far more than using a library in the first place. You can certainly implement your own big number class, but it's not trivial.

Member Avatar for ddanbe

Does your teacher know we live in century XXI?
I guess he is probably too lazy to write a new syllabus:(

Member Avatar for himgar

I also tried your program in Turbo C++. It worked and giving the result as expected.
I can understand your problem of using turbo c++ as I myself has undergone through such condition.

Also, I would suggest you to write int main() rather than void main() because the latter is deprecated and modern compilers even reject void main()

Member Avatar for Anuradha Mandal

It works correctly.himgar is right.

Be a part of the DaniWeb community

We're a friendly, industry-focused community of developers, IT pros, digital marketers, and technology enthusiasts meeting, networking, learning, and sharing knowledge.