Please help, 4 lines of errors i just cant solve!!!

[AShaw]

Hi, first post on this board so please be kind. Basically i'm writing a C code which is a modified version of the Newton method of root finding. It involves a few loops and looks like it should wortk but i keep getting these errors:

phy-pc3195:Desktop guest$ gcc Newton2.c -o Newton
Newton2.c: In function ‘main’:
Newton2.c:30: error: incompatible type for argument 3 of ‘f’
Newton2.c:35: error: incompatible type for argument 3 of ‘f’
Newton2.c: In function ‘newton’:
Newton2.c:53: error: incompatible type for argument 3 of ‘f’
Newton2.c:53: error: incompatible type for argument 3 of ‘f_prime’

Here's my code:

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

double newton(double x_0, double tol, int max_iters, 
          int* iters_p, int i, int* converged_p);
double f(double n, int i, double x[i]);
double f_prime(double n, int i, double x[i]);

int main() {
	int    i;        /* One of four temperature ranges*/
   double x_0;       /* Initial guess                 */
   double x[3];      /* Approximate solution          */
   double tol;       /* Maximum error                 */
   int    max_iters; /* Maximum number of iterations  */
   int    iters;     /* Actual number of iterations   */
   int    converged; /* Whether iteration converged   */
   float n;         /* Number density                */

   printf("Enter x_0, tol, and max_iters\n");
   scanf("%lf %lf %d", &x_0, &tol, &max_iters);
   for(n=0.01;n<=100;n=n*1.05) {
   	for(i=0;i<4;i++) {
   		
   x[i] = newton(x_0, tol, max_iters, &iters, i, &converged);

   if (converged) {
    printf("Newton algorithm converged after %d steps.\n", 
         iters);
    printf("The approximate solution is %19.16e\n", x[i]);
    printf("f(%19.16e) = %19.16e\n", x[i], f(n, i, x[i]));
   } else {
    printf("Newton algorithm didn't converge after %d steps.\n", 
          iters);
    printf("The final estimate was %19.16e\n", x[i]);
    printf("f(%19.16e) = %19.16e\n", x[i], f(n, i, x[i]));
  }
   	}}
   return 0;
}  /* main */


double newton(double x_0, double tol, int max_iters, 
          int* iters_p, int i, int* converged_p) {
   double x;
   double x_prev;
   int    iter = 0;
   float n;
   x=x_0;

   do {
      iter++;
      x_prev = x;
      x = x_prev - f(n, i, x_prev)/f_prime(n, i, x_prev);
   } while (fabs(x - x_prev) > tol && iter < max_iters);

   if (fabs(x - x_prev) <= tol)
      *converged_p = 1;
   else
      *converged_p = 0;
   *iters_p = iter;
   
   return x;
}  /* newton algorithm */


double f(double n, int i, double x[i]) {
	if (i=0) {
		return 1-((3.42e+16*pow(x[i],2.12)*n)/0.015);
	}
   else if (i=1) {
   	return 1-((9.10e+18*x[i]*n)/0.015);
   }
   else if (i=2) {
   	return 1-((1.11e+20*pow(x[i],0.56)*n)/0.015);
   }
   else if (i=3) {
   	return 1-((2.00e+8*pow(x[i],3.67)*n)/0.015);
   }
   else printf("Temperature outside the given range");
   
}  /* f */

double f_prime(double n,int i, double x[i]) {
   if (i=0) {
   	return (-7.2504e+16*pow(x[i],1.12)*n)/0.015;
   }
   else if (i=1) {
   	return (-9.10e+18*n)/0.015;
   }
   else if (i=2) {
   	return (-6.216e+19*pow(x[i],-0.44)*n)/0.015;
   }
   else if (i=3) {
   	return (-7.34e+8*pow(x[i],2.67)*n)/0.015;
   }
   else printf("Temperature outside given range");
}  /* f_prime */

Any help would be appreciated, thanks a lot.
Aarran

[Spidey]

phy-pc3195esktop guest$ gcc Newton2.c -o Newton
Newton2.c: In function ‘main’:
Newton2.c:30: error: incompatible type for argument 3 of ‘f’
Newton2.c:35: error: incompatible type for argument 3 of ‘f’
Newton2.c: In function ‘newton’:
Newton2.c:53: error: incompatible type for argument 3 of ‘f’
Newton2.c:53: error: incompatible type for argument 3 of ‘f_prime’

Firstly, Please use code tags.
<< !! Posting Code? Read this First !! >>

Second, All your errors are related to passing the wrong types to your functions, your prototype for the function f is defined as -

double f(double n, int i, double x[])

which means it expects a double, an int and a pointer.

and in lines 30 & 35 you are passing an element of the array instead of its address -

Element :

printf("f(%19.16e) = %19.16e\n", x[i], f(n, i, x[i]));

Address:

printf("f(%19.16e) = %19.16e\n", x[i], f(n, i, x));

Your other errors on line 53 are similar,-

Now, the same function expects an array however you are passing the simple double x_prev.

x = x_prev - f(n, i, x_prev)/f_prime(n, i, x_prev);