Help with a recursive function that computes a to the n

Hello!

I have been working on this for several days now and the program has no errors but it does not calculate. Here's the code:

Code:

---

#include "stdafx.h"
#include "stdio.h"
 
float power(float a, int n); // function prototype//
 
 
int main (void)
{
    float a;
 
    int n;
 
    printf("\n enter a value of a");
        scanf ("%f", &a);
        printf("\n enter value of n");
        scanf ("%f", &n);
    printf("\n %.4f to the power of % d is %.4f",a,n,power(a,n));
       
        return 0;
}
float  power(float a, int n)
{

    if (a==0)
    {
        return 0;
 
    }
    else if(n==0)
    {
        return 1;
 
    }
    else if (n>0)
    {
        return( a* power(a,n-1));
    }
    else
    {
        return ((1/a)*power(a,n+1));
    }
}

---

Please help me figure this out!

What's seems to be the problem? What is the output?

>> return ((1/a)*power(a,n+1));

Really?

The other problem with doing it this way is that your order of operations is out of whack too.

Quote:

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Originally Posted by master5001

>> return ((1/a)*power(a,n+1));

Really?

The other problem with doing it this way is that your order of operations is out of whack too.

---

No that looks right. a^-3 = (1/a)*a^-2 = (1/a)*(1/a)*a^-1=(1/a)*(1/a)*(1/a)*1.

He could compute 1/(a^n) in that final condition, but this should work almost as well.

Ah ok, fair enough, it is going "less than 0." Though I am still going to point out that one could theoretically be compounding floating point errors. I would still only do my division once to minimize floating point errors. But I am also one of those crazy types of guys who would typically subtract 1.0f from a floating value too....

Yes, that's why I said almost as well. But if the concern is precision, then the first thing to fix is to change float to double.

Either way, I am not spotting anything that would cause any sort of unusual returns. I would use a double for this. And even with a double I would still do: return 1.0 / power(a, -n); But that is just me.

When you're inputting n, being an integer, you should use

scanf ("%d", &n);
instead of
scanf ("%f", &n);

[sound of "doh!!"]

Quote:

---

Originally Posted by C_ntua

What's seems to be the problem? What is the output?

---

The problem is that the program does not seem to have the correct output. I attached a screenshot to explain what I mean!

Thanks!

Quote:

---

Originally Posted by nonoob

When you're inputting n, being an integer, you should use

scanf ("%d", &n);
instead of
scanf ("%f", &n);

[sound of "doh!!"]

---

Uh oh... Todd has some competition for the title of Ol' Eagle Eye. That looks like reason enough for your code to be broken by my count.

Being in a good mood today, here is a recap of all issues we have addressed.

Suggestions implemented:

Code:

---

#include "stdafx.h"
#include "stdio.h"
 
float power(float a, int n); // function prototype//
 
 
int main (void)
{
    float a;
    int n;
 
    printf("\n enter a value of a");
    scanf ("%f", &a);
    printf("\n enter value of n");
    scanf ("%d", &n);
    printf("\n %.4f to the power of % d is %.4f",a,n,power(a,n));

    return 0;
}
float  power(float a, int n)
{
    /* I put the numbers in float notation. Not a big thing. I am nit-picking. */
    if (a==0.0f)
    {
        return 0.0f;
 
    }
    else if(n==0)
    {
        return 1.0f;
    }
    else if (n>0)
    {
        return( a* power(a,n-1));
    }
    else
    {
        return (1.0f / power(a,-n)); // 1 extra recursion. 1 division
    }
}

---

Thank you all for your help! Now, what can I do to turn this into a non-recursive function.

Write it in a non-recursive way. If only there was a way to repeat a certain group of code while some condition remains true....

Ooooh ooooh ooooh pick me pick me!!!

Gotos?

Quote:

---

Originally Posted by nonoob

Ooooh ooooh ooooh pick me pick me!!!

Gotos?

---

Now, now, Johnny, you know what happens when you say ... that word.

/me throws tennis ball at head.

Anyone else?

Here is the code I am trying to compute for a non- recursive function now!
#include "stdafx.h"
#include "stdio.h"

double mypower(float a, int n); // function prototype//


int main (void)
{
float a;
int n;
int power;

printf("\n enter a value of a\n");
scanf ("%d", &a);
printf("\n enter value of n\n");
scanf ("%d", &n);
power=mypower (a,n);
printf("The result is %d\n", power);

return 0;
}
double power(float a, int n)
{
if (a==0.0)
{
return 0.0;

}
else if(n==0)
{
return 1.0;
}
else if (n>0)
{
return( a* mypower(a,n-1));
}
else
{
return (1.0/ mypower(a,-n));
}
}


The error is error LNK2019: unresolved external symbol "double __cdecl mypower(float,int)" (?mypower@@YANMH@Z) referenced in function _main
C:\Documents and Settings\Owner\My Documents\Visual Studio 2008\Projects\lab 8.3.2\Debug\lab 8.3.2.exe : fatal error LNK1120: 1 unresolved externals

double mypower(float a, int n);
double power(float a, int n)

Choose one.