a problem with my C code

Question

i got a problem with this code,

not sure what's the problem
would appreciate the help.

void Ex5()
{
double x, ans;
int n;
printf("Enter a real number >>> ");
scanf_s("%lf", &x);
printf("Enter a natural number >>> ");
scanf_s("%d", &n);
ans = f5(n, x);
printf("%.3lf\n", ans);

}
double f5(int n, double x)
{
double num, den, r, i = 2, sum = x - 1;
int p = 3;
while (p <= (2*n + 1))
{
den = ((factorial(p))*i);
r = x - 1;
num = pow(r, p);
sum += (num / den);
p += 2;
i++;
}

}
long factorial(int n)
{
long factor = 1, j;
for (j = 1; j <= n; j++)
factor *= j;
return factor;
}

Answer 1

Hello,
it looks like you are writing 32 bit code. Then long is 4 byte and double is 8 byte.
Look at your operation:

den = ((factorial(p))*i);

-> double = long * int

i will be converted to long. The result of the multiplication will be long again. Then you cast it to 8 byte double.
"long * long" can easily overflow. The compiler recognizes that you cast the result to 8 byte double, so that's why the compiler warns you.

Use this coding instead:

den = (double)factorial(p) * i;

-> long and int will be casted to double first. The multiplication will now operate on 8 byte doubles instead of 4 byte longs.

Regards, Guido