/* ------------------------------------------------------------------- 
//  Figure 15.9:  Writing a file of voltages.                           
// ------------------------------------------------------------------- 
*/
#include "tools.h"                                                         

#define V    10                     /* battery voltage */                    
#define TAU  0.15                   /* time constant for this circuit (s) */ 

#define step  (1.0 / 15.0)          /* time step for lines of table */       
#define epsilon (step / 2.0)        /* for floating comparison to end loop */ 

double f( double t ) {  return V * (1 - exp( -t / TAU )); }  

void main( void )                                     
{
    double t;                           /* time since switch closed */  
    double v;                           /* voltage at time t */   
    char table;                         /* 'y' for table, else coordinate format */  

    string format = "(%.2f, %.2f)\n";   /* format for coordinate output */  
    stream myfile = fopen( "voltage.dat", "w" );    

    if (myfile == NULL)  fatal( "Cannot open voltage.dat" );

    printf( "\n Write output in table form (y/n)? " ); 
    scanf( " %c", &table );
    if (tolower( table ) == 'y') {
        fprintf( myfile, "    time         voltage \n\n" ); /* table headings */  
        format = "%8.2f %14.2f\n";
    }
    
    printf( "\n Writing table to file voltage.dat\n" );  
    for (t = 0.0; t <= (1.0 + epsilon); t += step ) {                                        
        v = f( t );                                       
        fprintf( myfile, format, t, v ); 
    }                     
    fclose( myfile );
    bye();
}