#include <stdio.h>
float pows(float,float);
int main()
{
float num,base;
printf("enter base followed by power integer.");
scanf("%f %f",&base,&num);
printf("%f ",pows(base,num));
return 0;
}
float pows(float base,float n)
{
if(n==0)
return(1);
else if(base==0)
return(0);
else
for(;n>=1;n--)
{ return(base*pows(base,n-1));/*recursive*/
}
}
D33wakar 36 Posting Whiz in Training
WaltP 2,905 Posting Sage w/ dash of thyme Team Colleague
Other than it doesn't work properly, do you have a question? Or is this an ego-post?
TrustyTony 888 ex-Moderator Team Colleague Featured Poster
%f and float n does not look integer to me, like your prompt and algorithm suggests.
TrustyTony 888 ex-Moderator Team Colleague Featured Poster
Also you are doing both iteration and recursion same time, chose which one.
D33wakar 36 Posting Whiz in Training
Other than it doesn't work properly
yeah.I know it's not perfect.But couldn't find other bugs 'cept its smaller range.
See,that's why I posted this in discussion thread.
Or is this an ego-post?
No,this is not "an ego-post".
do you have a question?
The thing is ,I didn't came up with any while posting.
So I just posted the code(looking for advice).
%f and float n does not look integer to me, like your prompt and algorithm suggests.
I was using int(egers) before,float was used to increase it's range.
I overlooked this line
printf("enter base followed by power integer.");while changing to float.
Also you are doing both iteration and recursion same time, chose which one.
Am I supposed to do either iteration or recursion only(i.e.no need to both)?
D33wakar 36 Posting Whiz in Training
It has got MAJOR precision issues.
How do I make it accept negative "power" argument
pows(100,-2) gives nothing.
TrustyTony 888 ex-Moderator Team Colleague Featured Poster
Your algorithm can not deal with fractions, so you should take long, not float argument. But I doubt that C can deal with bigger than int range of powers if you are not dealing with very small numbers (which also would could take quite a while as you are recursing every single number from n to 1).
For efficiency you maybe should take a look at least for the recursive power algorithm:
http://www.catonmat.net/blog/mit-introduction-to-algorithms-part-two/
As for negative powers, how were you teached to do them in school with positive powers? You must also do that adaptation to the recursive algorithm's pseudocode.
WaltP 2,905 Posting Sage w/ dash of thyme Team Colleague
looking for advice).
Then why didn't you say so? Posting only code says "Look at my code! Ain't it great?" That's an ego-post. If you simply added "I'm looking for advice on making this code better" you would get more useful responses right away.
D33wakar 36 Posting Whiz in Training
I trimmed the precious one a little bit and used double instead of float.
#include <stdio.h>
double pows(double,double);
int main()
{
double num,base;
printf("enter base followed by power.");
scanf("%lf %lf",&base,&num);
printf("%lf ",pows(base,num));
return 0;
}
double pows(double base,double n)
{
if(base==0)
return(0);
else if(n==0)
return(1);
else if(n>=1)
{
return(base*pows(base,n-1));/*for positive powers*/
}
}To make it work with negative powers I was thinking like this...
else if(n<=-1)
{ n=abs(n);/* abs()--->#include <complex.h> */
return((base)/pows(base,n+1));/*for negative powers*/
}But it doesn't work that way.Here abs(n) returns zero.
something's wrong with the implementation?what should I do then?
By the way I tried the algorithm suggested inhttp://www.catonmat.net/blog/mit-int...thms-part-two/
It worked fine (but not with long arguments) .Anyways,thanks for that pyTony.
WaltP 2,905 Posting Sage w/ dash of thyme Team Colleague
It also doesn't work if you input
12 2.5
An infinite loop is not an appropriate answer either.
TrustyTony 888 ex-Moderator Team Colleague Featured Poster
Hint: a**-1 == 1/a
D33wakar 36 Posting Whiz in Training
Hint: a**-1 == 1/a
yeah, that's what I did here.
double pows(double base,double n)
{
if(base==0)
return(0);
else if(n==0)
return(1);
else if(n>=1)
{
return(base*pows(base,n-1));/*for positive powers*/
}
else if(n<=-1)
{ n=-n;
return((base)/pows(base,n+1));/*for negative powers*/
}
}for positive value:
pows(10,22) gives 10000000000000000000000.000000
but pows(10,23) gives 99999999999999992000000.000000------>(Now, where did that come from?)
for negative value:
pows(10,-6) gives 0.000001
pows(10,-7) gives 0.000000------>(how to increase its range?)
It also doesn't work if you input
12 2.5
Yeah I'll deal with those kinda fractions later.First negative exponentiation.
TrustyTony 888 ex-Moderator Team Colleague Featured Poster
Change the format to printing of the result to %g (scientific notation).
I do not understand why do you write negative powers so as you write instead of simple 1./pows(base, -n), even it seems to work.
D33wakar 36 Posting Whiz in Training
I do not understand why do you write negative powers so as you write instead of simple 1./pows(base, -n), even it seems to work.
I didn't understand what you're trying to say.Can you "please" show it in c code.
Now, we need to handle powers in fractions like 1/2,2/3,5/7...similarly
-1/2,-3/2,-3/7...etc.
Can anyone help me figure out the solution,
OR suggest a better algorithm.
TrustyTony 888 ex-Moderator Team Colleague Featured Poster
Generally if you deal with non-integer numbers as powers you would use exponentiation with multiplication of logarithms.
My comment was about this 'interesting' lines:
else if(n<=-1)
{ n=-n;
return((base)/pows(base,n+1));/*for negative powers*/
}which mean:
else if(n<=-1) return 1./pows(base,-n);and in main:
printf("%g ",pows(base,num)); D33wakar 36 Posting Whiz in Training
Yeah thanks pyTony, I really appreciate that.Now it's crystal clear to me.
For the power of fractions like 1/2,2/3,5/2 etc:
If we had to do like pows(12,2.5)
we could do like this:- 12 ^ 5/2 can be written as (12 ^ 5)^1/2
and (something)^1/2 means sqrt of (something).
Hence we need an algorithm to find not just square root or cube root but nth root of a number.Can anyone help me with that?
TrustyTony 888 ex-Moderator Team Colleague Featured Poster
D33wakar 36 Posting Whiz in Training
Used a code in here to produce sqrt and rest is here.
#include <stdio.h>
#include "sqroot.h"
double pows(double,double);
double pows_f(double,int,int);
int main()
{
double base,num;
int num_rt,denum_rt;
printf("enter Base followed by Numerator and then Denominator\n.");
scanf("%lf %d %d",&base,&num_rt,&denum_rt);
printf("%lf ",pows_f(base,num_rt,denum_rt));
return 0;
}
double pows(double base,double n)
{
if(base==0)
return(0);
else if(n==0)
return(1);
else if(n>=1)
{
return(base*pows(base,n-1));/*for positive powers*/
}
else if(n<=-1)
{
return(1/pows(base,-n));/*for negative powers*/
}
else
printf("error!");
return(0);
}
double pows_f(double base,int num,int denum)/* num means numerator & denum means denomenator*/
{
double root_ed,pows_ed;/* variables to store root(ed) value & pows(ed) value*/
pows_ed=pows(base,num);
return root(pows_ed,denum);
}pows_f(5,1,2)--->5^1/2 =2.236068
pows_f(17,3,2) = 70.092796
pretty close .
D33wakar 36 Posting Whiz in Training
The above code doesn't need variable root_ed,I forgot to remove it
(man!What was I thinking).and also to use %g(scientific format).
D33wakar 36 Posting Whiz in Training
Alright.Everything's fine except one thing.
I need pows_f to accept usually two arguments(sometimes three).Can we do that in C?
If I need to find out 25^13 I need to enter as pows_f(25,13,1)
Can we make the third argument optional(i.e. should be given only when required)
for e.g to find 25^13 as pows_f(25,13) only and to find 25^3/4 as pows_f(25,3,4).
TrustyTony 888 ex-Moderator Team Colleague Featured Poster
D33wakar 36 Posting Whiz in Training
I looked at the example there.It seems totally different case than mine.
I don't know How to use it in my code.It would be great help if you'd show me an example of it(a case like mine).
TrustyTony 888 ex-Moderator Team Colleague Featured Poster
After reading further and going over the hurdle of dropped underlines from my googled source, I noticed that in C there is not support for automatic count of parameters. So it is only usefull if you give is_rational as extra parameter, which kind of beats the purpose. So you are better of just having two versions of funcition or maybe having the power as string and detecting '/' in it or not and parsing accordingly.
D33wakar 36 Posting Whiz in Training
Here it is.
#include <stdio.h>
#include "sqroot.h"
double pows(double,double);
double pows_f(double,int,int);
int main()
{
double base,num;
char power[10];
int num_rt,denum_rt;
int i,j,is_rational;
printf("enter Base followed by power\n.");
scanf("%lf %s",&base,power);
for (i=0;i<=sizeof(power);++i)
{
if(power[i]=='/') /*rational*/
{
num_rt=power[0]-48;
for(j=0;j+1<i;j++)
{
num_rt=num_rt*10+(power[j+1]-48);/* ascii value of character 1 is 49*/
}
denum_rt=power[i+1]-48;
for(j=i+1;j+1<strlen(power);j++)
{
denum_rt=denum_rt*10+(power[j+1]-48);/*similar to num*/
}
is_rational=1;
}
}
if(is_rational!=1) /* not rational*/
{
num_rt=power[0]-48;
for(j=0;j+1<strlen(power);j++)
{
num_rt=num_rt*10+(power[j+1]-48);/* ascii value of char 1 is 49*/
}
denum_rt=1;
}
printf("%g ",pows_f(base,num_rt,denum_rt));
return 0;
}
double pows(double base,double n)
{
if(base==0)
return(0);
else if(n==0)
return(1);
else if(n>=1)
{
return(base*pows(base,n-1));/*for positive powers*/
}
else if(n<=-1)
{
return(1/pows(base,-n));/*for negative powers*/
}
else
printf("error!");
return(0);
}
double pows_f(double base,int num,int denum)/* num means numerator & denum means denomenator*/
{
double pows_ed;/* variables to store pows(ed) value*/
pows_ed=pows(base,num);
return root(pows_ed,denum);
} Be a part of the DaniWeb community
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