assignment-2.c

#include <stdio.h>
#include <stdarg.h>
#include <signal.h>
#include <string.h>
#include <stdlib.h>
// 
// Please compile with this arg -std=c99 when using GCC 4.x.
// commenting with double slash and inline function are C99's feature
//

// function prototype
static inline double temperature(double);
static inline double Celsius2Fahrenheit( double celsius );
static inline double Fahrenheit2Celsius( double fahrenheit );
static inline double Average( int portion, ... );
static inline double AverageTemperature( double time );

// main function
int main( void ) {

  FILE *input = fopen( "input.dat", "r" );
  if ( input == NULL ) { 
    printf( "Input file could not be opened. Interupt program now.\n" );
    raise( SIGINT );
  }
  rewind( input ); // move file point back to head of file

  char line[ 5 ];
  fgets( line, 5, input );
  
  char *tokenPtr;

  tokenPtr = strtok( line, " " ); double hr = atof( tokenPtr );

  tokenPtr = strtok( NULL, " " ); double min = atof( tokenPtr );

  double time = hr + min / 60; printf( "time is %.2f hours\n", time );

  double celsius = AverageTemperature( time );
  double fahrenheit = Celsius2Fahrenheit( celsius );

  printf( "average is %.2fºC or %.2fºF\n", celsius, fahrenheit );

  FILE *output = fopen( "output.dat", "w" );
  if ( output == NULL ) { 
    printf( "Output file could not be opened. Interupt program now.\n" );
    raise( SIGINT );
  }

  fprintf( output, "%f%s", fahrenheit, "ºF" );

  return 0;

}

// implementation
static inline double temperature( double t ) {
  return ( 4 * t * t * t ) / ( t + 2 ) - 20;
}

static inline double Celsius2Fahrenheit( double celsius ) {
  return ( 9.L * celsius / 5.L ) + 32.L;
}

static inline double Fahrenheit2Celsius( double fahrenheit ) {
  return ( 5.L / 9.L ) * ( fahrenheit - 32.L );
}

// ... is a macro defined in stdarg.h for receiving variable arguments
static inline double Average( int portion, ... ) { 

  double total = 0;
  
  va_list ap;

  va_start( ap, portion );

  for( int i = 1 ; i <= portion ; i++ ) {
    total += va_arg( ap, double );
  }

  va_end( ap );

  return total / portion;
}

static inline double AverageTemperature( double time ) {
  double segment = time / 5.L;
  return Average(
    6,
    temperature( 0 ),
    temperature( segment ),
    temperature( segment * 2 ),
    temperature( segment * 3 ),
    temperature( segment * 4 ),
    temperature( time )
  );
}