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

double f(double x);
void secant(double x0, double x1, double tol, int max_itno);
void plotfunction(double x0, double x1,int N);

// Driver program
int main() 
{ 
    // Initial values
    double x0 =-4, x1 = -3; 
    secant(x0, x1,1e-16,10000); 
    plotfunction(-10, 10,1000);

    return 0; 
} 


// Prints root of func(x) with error of EPSILON 
void secant(double x0, double x1, double tol, int max_itno) 
{ 
   int i;
   double x;
   FILE *output;
   output = fopen("secant.dat", "w");//opening file. 

    i=0;
    x=x1;
    while (fabs(f(x)) >= tol&&i<max_itno) 
    { 
        fprintf(output,"%.15f\t%.15f\n",x0,f(x0));
        fprintf(output,"%.15f\t%.15f\n",x1,f(x1));


        x = x1-f(x1)*(x1-x0)/(f(x1)-f(x0)); 
        x0=x1;
        x1=x;
        printf("iteration number: %d \tf(%.15lf) = %.15lf\n",i,x,f(x));
        fprintf(output,"%.15f\t%.15f\n",x,0.000);
        fprintf(output,"%.15f\t%.15f\n\n",x,f(x));

       i++;
    } 
} 

// Define function

double f(double x) 
{ 
    double y;

y=cos(x)-x;
    return y;
} 

void plotfunction(double x0, double x1,int N)
{ int i;
  double x,dx;
  FILE *output;

      dx=(x1-x0)/N;


output = fopen("function.dat", "w");//opening file. 
 for(i=0;i<N;i++){
    x=x0+dx*i;
fprintf(output,"%.15f\t%.15f\n",x,f(x));
 }
 
 fclose(output);//closing file.

}