//DO NOT USE FOR SCHOOL PROJECTS!!!!
// Notify author on v.i.c.l.i.c.k@hotmail.com if you plan to use any part of this code between keywords "main" and "act_tanh"!!!!
//Otherwise use of this code is strictly prohibed.


#include <stdio.h>
#include <stdlib.h>
#include <ctype.h>
#include <limits.h>
#include <string.h>
#include <errno.h>
#include <math.h>

double tanh_(double x, double precision);

int main(void)
{
    double x,precision,result,precise;

    printf("Zadejte x: ");
    scanf("%lf",&x);
    printf("\n\nZadejte presnost: ");
    scanf("%lf",&precision);
    result=tanh_(x,precision);
    precise=tanh(x);


    printf("Vypocitano: %1.15e \n \nPresne: %1.15e",result,precise);
    printf("\n\n Rozdil: %1.15e",result-precise);
    printf("\n\nPresnost: %1.15e \n\n",precision);
    return EXIT_SUCCESS;
}











double tanh_(double x, double precision)
{
if(x>20)
    return 1;

else if(x<(-20))
    return (-1);

else if(x<=0.000005&&x>=(-0.000005))
    return x;

double sinh_inc,sinh_=x,cosh_inc,cosh_=1,ant_tanh,act_tanh,x2=x*x;
double difference;
double c_inc_numerator=1,c_inc_denominator=1,k=0;
double s_inc_numerator=x,s_inc_denominator=1;
    while(1)
    {
        ++k;

        //cosh
        c_inc_numerator*=x2; //x^(2*(k+1))=x^2k * x^2
        c_inc_denominator*=((k+k-1)*(k+k)); //(2k+1)! = 2k! * 2k+1 * 2k+2

        cosh_inc=(c_inc_numerator)/(c_inc_denominator);
        cosh_+=cosh_inc;


        //sinh
        s_inc_numerator=c_inc_numerator*x;
        s_inc_denominator=c_inc_denominator*(k+k+1);

        sinh_inc=s_inc_numerator/s_inc_denominator;
        sinh_+=sinh_inc;


        //division >> tanh
        ant_tanh=act_tanh; //store previous result
        act_tanh=((sinh_)/(cosh_)); //make actual result
        difference=ant_tanh-act_tanh; //calculate the difference
        difference=difference<0?(-difference):difference; //make absolute value

        if (difference<=precision)
        return act_tanh;
    }


}