Thread: Problem with "Casting"

Originally Posted by vart

is n initialized?

yeah!

Try separating out every single operation to its own statement (on its own line) and make sure the values that you get are what you expect.

well, i forgot to put ";" in

Code:

 float z= 1/2.0-x*tan(x)+x

but...

It does actually help if you provide actual code that illustrates your problem, rather than paraphrasing. The code as given will not even compile.

There is no header named stdio. It is either stdio.h (from C) or cstdio (C++). There is no header named stlib. Presumably you mean either stdlib.h or cstdlib

You are missing a semi-colon from the first line of foriginal() which also means the code will not compile.

There are some minor issues due to implicit conversions between types in your code (eg when PI is substituted, the compiler will see a literal of type double) but that observation does not explain you getting a runtime error.

Try cutting and pasting actual code that illustrates your problem, and info such as what compiler/settings you are using, rather than playing "blind mans bluff" with us.

As grumpy stated, if you give code that is different than what you're using, then we can't help you find the problem.

Find exact code that gives the error for you, then copy and paste it into a post.

Also, are you sure the error you are getting is not somewhere else in the code?

(2*1+1)*PI/2.0-PI/180.0 is 3*PI/2 - 0.01745 which is 4.712-0.01745 which is about 4.69. That's hardly something that should cause a runtime error.

Assuming his code is vaguely correct, my guess is 'fabs(xn-x)'.

Check 'xn' and 'x' for validity... the expression can raise a floating point exception, I believe, if either is NAN.

Soma

here it goes the original

Code:

#include<stdio>
#include<stdlib>
#include<iostream>
#include<math>
#define PI 3.14159265358979324

using namespace std;
float foriginal( float x)
   {
     float z=1/2.0-x*tan(x)+x;
     return(z);
   }

 float iterar(int n)
  {

    float a,b,xn,x,c,eps;
    eps=0.001;
    c= (float) (2*n +1)* PI/2.0 - PI/180.0 ; //when i==1 the error appears!!!!!
    xn=c;
    do
     {
       x=xn;
       xn=foriginal(x);
     }
    while (fabs(xn-x)>eps);
    printf("The root is  = &#37;9.7f           , f(x)= %9.7f \n",x,foriginal(x)-x);
  }

  int main()
    {
       int i; float a,b;
       for(i=0;i<10;i++)
         {
           iterar(i);
         }

    }

yeah, it has stable solution every interval -PI/2 + kPI,PI/2 + kPI, k belongs to integer set

Narrow it down some more. You say it happens when i is 1, right? So change main to this:

Code:

  int main()
    {
       iterar(1);
    }

Does it still happen then? If not, then what is i when it happens?

If yes, then change your iterar function to this:

Code:

 float iterar(int n)
  {

    float a,b,xn,x,c,eps;
    eps=0.001;
    c= 4.6949358; //when i==1 c will be this anyway.
    xn=c;
    do
     {
       x=xn;
       xn=foriginal(x);
     }
    while (fabs(xn-x)>eps);
    printf("The root is  = %9.7f           , f(x)= %9.7f \n",x,foriginal(x)-x);
  }

Does it still happen then? If yes, then obviously that line is not your problem. If no, then move that line to its own program and see if it still causes a problem.

no, i did not miss anything

I thought that the problem was the "CASTING", c is float, n is integer...