/* ------------------------------------------------------------------------  
// Figure 3.9:  An action with an alternative.                                        
// ------------------------------------------------------------------------ 
// This program will determine the velocity and distance travelled by a  
// grapefruit with no initial velocity, t seconds after being dropped     
// from a building.  Input time value is checked for being positive.     
*/

#include <stdio.h>
#define GRAVITY  9.81   /* gravitational acceleration (meters/seconds) */

void main( void )                                                                  
{
    double t;           /* elapsed time during fall (s) */        
    double y;           /* distance of fall (m)         */
    double v;           /* final velocity (m/s)         */ 
    
    printf( "\n\n Welcome.\n"
            " Calculate the height from which a grapefruit fell\n"
            " given the number of seconds that it was falling.\n\n" );

    printf( " Input seconds: " );   /* Prompt for the time, in seconds. */
    scanf( "%lg", &t );             /* keyboard input for time */          

    if (t > 0) {                    /* check for valid data */
        y = .5 * GRAVITY * t * t;   /* calculate the distance of the fall */
        v = GRAVITY*t;              /* velocity of grapefruit at impact */ 
        printf( "    Time of fall = %g seconds \n", t );
        printf( "    Distance of fall = %g meters\n", y );        
        printf( "    Velocity of the object = %g m/s \n", v );
    }
    else {                          /* otherwise, */
        puts( " Try again; input must be a positive number." );
    }

    puts( " Normal termination.\n" );
}