macOS How to insert natural logarithm in C.Urgent...

[gusious]

Hi.This is a bit urgent....

I am writing a program in C and i need to insert ln(natural logarithm).How do i do that?

 

[luckylefty01]

#include <math.h>

log(number); // Computes the ln of number


Is that what you need?

 

[gusious]

That's what i have inserted but i have this message: error: invalid lvalue in assignment

What's that?Oh,should i declair the value ln(number) which is ln(pi)+=log(pi) as float?

 

[luckylefty01]

I think your problem is that ln(pi) is not a variable; thus, you can't use it on the left side of an assignment.

I think what you want is:

double result;
result = log(pi)+log10(pi); //assigns the result of ln(pi) plus log(base ten)(pi) to result.

 

[Eraserhead]

You use log(x) to calculate the natural logorithm of x. C is like mathematicians, who use log to mean the natural log rather than ln.

see man math on the command line for this information.

 

[gusious]

No i don't need log.I only need ln.Wait a sec.Or more.I had an idea...

Check this out:

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

main()
{
float H,pi;
int n,ni,i,x[1000],y[1000],points;


points=0;
printf("insert ni and n\n");
while(scanf(" %d %d ",&ni,&n) ==2)
{
x[points]=ni;
y[points]=n;
points++; }
pi=0;
H=0;
for(i=0; i<points; i++)
{
pi= pi + x/y;
}

H=-(pi*ln(pi));
printf("The pi is %f,the ln(pi) is %f and the H is %f\n",pi,ln(pi),H);
}

I want to calculate the sum pi*ln(pi).So,can you find me the problem?

 

[Nuc]

Listen to Eraserhead

Change ln(...) to log(...) like he said. If you're not satisfied with his answer then try it and then double check it with your calculator...

Nuc

 

[Sayer]

Change 'ln' to 'log'.

In programming log(N) is the natural log of N.

Of course the program will never end unless you error it somehow. Glad I never wasted time "learning" programming in school. I wonder how anyone gets anywhere at first.

 

[gusious]

Yup.I just saw that and correct it.

 

[Enuratique]

Check this out:

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

main()
{
float H,pi;
int n,ni,i,x[1000],y[1000],points;


points=0;
printf("insert ni and n\n");
while(scanf(" %d %d ",&ni,&n) ==2)
{
x[points]=ni;
y[points]=n;
points++; }
pi=0;
H=0;
for(i=0; i<points; i++)
{
pi= pi + x/y;
}

H=-(pi*ln(pi));
printf("The pi is %f,the ln(pi) is %f and the H is %f\n",pi,ln(pi),H);
}

I want to calculate the sum pi*ln(pi).So,can you find me the problem?

I see you've got it now...