CODEWITHSUNDEEP
ccommand-line-argumentsvariadic-functions
Suryasnata Saha
Suryasnata Saha

Reputation: 13

Why is my code not generating factorial after 9?

Write a program in C to compute the factorial of the numbers passed from the command line. The factorial must be computed in a separate function called computeFact( ) which has the following prototype: int computeFact(int,…);

#include <stdarg.h>
#include <stdio.h>
#include<stdlib.h>
int computeFact(int, ...);
int main(int argc, char *argv[]) 
{
  if (argc < 2) 
  {
    printf("Invalid!");
  } else {
    for (int i = 1; i < argc; i++)
    {
      int n = atoi(argv[i]);
      printf("Factorial of %d is %d\n", n, computeFact(n));
    }
  }
  printf("\n");./
  return 0;
}
int computeFact(int num, ...) 
{
  va_list valist;
  int fact = 1;

  va_start(valist, num);
  for (int i = 0; i < num; i++) 
  {
    int x=va_arg(valist, int);
    if(x==0)
      return 1;
    else
    {
    for(int j = 1; j <= x; j++)
       fact=fact*j;
    return fact;
    }
  }
  va_end(valist);
}

The output is as follows:

~$ ./1 1 2 3 4 5 6 7 8 9 10
Factorial of 1 is 1
Factorial of 2 is 2
Factorial of 3 is 6
Factorial of 4 is 24
Factorial of 5 is 120
Factorial of 6 is 720
Factorial of 7 is 5040
Factorial of 8 is 40320
Factorial of 9 is 362880
Factorial of 10 is 1

~$ ./1 0
Factorial of 0 is 1

~$ ./1 99
Factorial of 99 is 362880

~$ ./1 98
Factorial of 98 is 40320

~$ ./1 5
Factorial of 5 is 120

I think there is some error in converting string to int, as only last digit in two digit numbers is taken up for calculating factorial, but I am not able to identify what exactly to correct in my code.

Upvotes: 0

Views: 92

Answers (2)

Hamza
Hamza

Reputation: 560

Try below code:

int computeFact(int num, ...) 
{
  int fact = 1;

  int x = num;
  if(x==0)
    return 1;
  else
  {
    for(int value = 1; value <= x; value++)
      fact=fact*value;
    return fact;
  }
}

Upvotes: 0

MikeCAT
MikeCAT

Reputation: 75062

You are invoking undefined behavior by reading an argument that doesn't exist via va_arg.

It looks like you should stop using va_* macros and simply use the argument num in this case.

int computeFact(int num, ...) 
{
  int fact = 1;

  int x=num;
  if(x==0)
    return 1;
  else
  {
    for(int j = 1; j <= x; j++)
      fact=fact*j;
    return fact;
  }
}

Also be aware of the limitation of int. 99! will be 156 digits in decimal and it won't fit in the range of typical int (upto 2,147,483,647 = 2**31 - 1).

Upvotes: 5

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