/* --------------------------------------------------------------------- 
// Figure 6.15: Input validation using for.
//              Also demonstrates input validation using while.
// --------------------------------------------------------------------- 
// Compute the average speed of your car on a trip. 
*/
#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: " );          
    for(;;) {                                                          
        scanf( "%lg%lg", &hours, &minutes );                       
        hours = hours + ( minutes / 60 );                            
        if (hours >= 0.0) break;    /* Leave loop if input is valid. */
        printf( " Please re-enter; time must be >= 0: " );
    }
    miles = end_miles - begin_miles;
    speed = miles / hours;      
    printf( " Average speed was %g \n", speed );
    puts( " Normal termination.\n" );
}