Need help in doing math calculation for natural logarithm (ln)

Question

How do I write a function for this in C language?

y = 20 ln (x + 3) ?

How do I write the ln function?

Solution 1

#include <math.h> 

double fun(double x)
{
    return 20 * log( x + 3 );  //base-e logarithm!
}

//usage
double y = fun(30);

For base-10 logarithm, use log10().

Solution 2

double myfunction(int x){
    return  (20* log(x+3) );
}

?

And you call it :

double y = myfunction(yourX);

Solution 3

#include <math.h>
double function(double x)
{
     double y = 20 * log(x + 3.0);
     return y;
}

Solution 4

The log function in the c library is performs a natural logarithm ('ln'). See this for more details: CPlusPlus - log

Solution 5

Although the question is tagged C++, questioner is asking for a C implementation:

#include <math.h>

double myFunction(double x) {
    return 20.0 * log(x + 3.0);
}

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Comments

[Stephen Canon]

This is C++; the question asks for C.

[R.. GitHub STOP HELPING ICE]

Remove the std:: and the useless temp variable.

[John Bode]

Don't forget to #include <math.h> and to link against the math library if necessary.

[ronag]

Changed it to C. I kept the variable to keep it concrete in relation to the OPs question.