/* --------------------------------------------------------------------- 
//  Figure 3.14: Input validation using while.
//               Compute the average speed of your car on a trip. 
// --------------------------------------------------------------------- 
//  Test plan:
    begin       end     distance    hr/min    speed
    --------------------------------------------------
    61234       61475       241     4 51      49.69072
    -1          -61521
    61234       61521       287     5 28      52.5
    23498       22222
                -32222
                32222       8724    148 43    58.6619 
    23498       32222       8724    -148 43
                                    1 -70
                                    148 -17   59.0590  
*/

#include <stdio.h>
void main( void )
{   
    int begin_miles;    /*  Odometer reading at beginning of trip.   */ 
    int end_miles;      /*  Odometer reading at end of trip.         */ 
    int miles;          /*  Total miles travelled.                   */ 
    double hours;       /*  Duration of trip (hours, minutes).       */ 
    double minutes;      
    double speed;       /*  Average miles per hour for trip.         */ 
    
    puts( "\n Miles Per Hour Computation \n" );   

    printf( " Odometer reading at beginning of trip: " ); 
    scanf( "%i", &begin_miles );
    while (begin_miles < 0) {
        printf( " Please re-enter; odometer reading must be positive: " );
        scanf( "%i", &begin_miles );
    }

    printf( " Odometer reading at end of trip: " ); 
    scanf( "%i", &end_miles );
    while (end_miles < begin_miles) {
        printf( " Re-enter; input must be > first odometer reading: " );
        scanf( "%i", &end_miles );
    }
    
    printf( " Duration of trip in hours and minutes: " ); 
    scanf( "%lg%lg", &hours, &minutes );
    hours = hours + ( minutes / 60 );
    while ( hours < 0.0 ) {
        printf( " Please re-enter; time must be >= 0: " );
        scanf( "%lg%lg", &hours, &minutes );
        hours = hours + (minutes / 60);
    }
    miles = end_miles - begin_miles;
    speed = miles / hours;      
    printf( " Average speed was %g \n", speed );
    puts( " Normal termination.\n" );
}