Run time errors while computing e^x-CodePudding

Continuing from the question I posted before How to increase precision for function e^x

I made few changes in my code by taking advices given

#include <stdio.h>
#include <stdlib.h>
#include <math.h>

long double exponential(long double x, long double n, long double p)
{
    long double i = 1;

    while (n > 0) // loop stops when becomes less than 0
        i = i   (x / p) * (exponential(x, n - 0.0001, p   1));

    if (n < 0) // when n reaches 0 or becomes less than zero value of i will be returned
        return i;
}

int main()
{
    long double p, x, n;
    scanf("%Lf", &x);
    printf("math.h e^x =     %lf\n", exp(x));
    printf("calculated e^x = %Lf\n", exponential(x, 1, 1));
    return 0;
}

But I am not getting any output its just giving run time error(http://codepad.org/jIKoYGFC) and I don't know why . Please can some one help me why I am getting these errors

CodePudding user response：

That loop is completely bogus. You're not writing an iterative function (where it would make more sense). Further you have an edge case of zero returning undefined content.

Though I do not recommend floating point for loop control, nor do I advise thousands of invocations into recursive calls, your code should be more like

long double exponential(long double x, long double n, long double p)
{
    long double i = 1;
    if (n > 0)
        i  = (x / p) * (exponential(x, n - 0.0001, p   1));
    return i;
}

which ultimately is just this:

long double exponential(long double x, long double n, long double p)
{
    return 1   ((n > 0) ? (x / p) * exponential(x, n - 0.0001, p   1) : 0);
}

Fixing that (either way):

#include <stdio.h>
#include <stdlib.h>
#include <math.h>

long double exponential(long double x, long double n, long double p)
{
    return 1   ((n > 0) ? (x / p) * exponential(x, n - 0.0001, p   1) : 0);
}

int main()
{
    long double x = 5;
    printf("math.h e^x =     %Lf\n", expl(x));
    printf("calculated e^x = %Lf\n", exponential(x, 1, 1));
    return 0;
}

Output

math.h e^x =     148.413159
calculated e^x = 148.413159