Thread: Help with programming assignment

Hello!

I am fairly new to programming. I am trying to finish this assignment from Hanley's C Program Design for Engineers. It is due on Monday, and I am trying to get it finished up this evening. I think there is either something wrong with my for loop or with the equation I am using.
When I compile and run my program, I am able to get it to print in a list the volume, but as for the pressure, it is printing out "nan".

What do I need to tweak?

Code:

/****************************************************************************************
* Name: main
* Returns: int; 0 for success
*
* Purpose:  to compute Van der Waals equation of state for a gas. 
* Requires:  stdio library function, printf, scanf, 
* Dependencies:  none
****************************************************************************************/


/*includes*/
#include <stdio.h>
#include <math.h>

/*define contstants for Van der Waals' equation*/
#define R 0.08206
#define A 3.592
#define B 0.0427
/*******************************************************************
*  This is the main function
********************************************************************/
void instruct(void);

int main(void)
{


  double n_moles; /*the number of moles the user inputs*/
  double int_volume; /*the initial volume as input by the user*/
  double kelvin_temp; /*the temperature in Kelvins as input by user*/
  double increment_vol; /*the increment volume given by the user*/
  double final_vol; /*the final volume given by the user*/
  double pressure; /*the pressure*/
  double volume; /*volume*/
  instruct ();

  


  printf("\n\n\nPlease input the quanity of carbon dioxide (moles)>>");
  scanf( "%lf", &n_moles);

  printf("\n\nTemperature (Kelvins)>>");
  scanf( "%lf", &kelvin_temp);

  printf("\n\nInitial volume (milliliters)>>");
  scanf("%lf", &int_volume);

  printf("\n\nFinal volume (milliliters)>>");
  scanf("%lf", &final_vol);

  printf("\n\nVolume increment (milliliters)>>");
  scanf("%lf", &increment_vol);


  printf("Volume (ml)               Pressure (atm)");


  /*P =( nRT/(Vnb))-n^2a/V^2*/
  pressure = ( n_moles*R*kelvin_temp/(volume*n_moles*B))-n_moles*n_moles*A/volume*volume ;

  {
    
    for (volume =int_volume;
	 volume  <= final_vol;
	 volume +=increment_vol)
      



  printf("\n\n%5.4lf         %5.4lf\n",volume, pressure);

    }
 return 0;


} // end function main () ************************************** 



/*******************************************************************
* This is the instruct function--it gives instructions to the user
*******************************************************************/


void instruct (void)
{

	printf("\n\n\nPlease enter at the prompts ");
	printf("the number of moles of carbon dioxide ");
	printf("the absolute\n temperature, the initial volume in millimeters ");
	printf("the final volume, \nand the increment volume between lines of the table\n\n");
}

Thanks for your help!
Sarah

You need to put the computation inside the for loop. (You need to re-compute pressure for each volume, right?)

Thanks for your comments! My code works now, everything is displayed correctly. Whoo!