Journey time prog 1 minute wrong

I wrote a program for an assignment to calculate journey times. There is a problem since sometimes (not allways) the journey time returned is 1 off what its meant to be. I tried several different things but cnat seem to find why

Code:

#include <stdio.h>
#include <conio.h>

               /*TASK 5: JOURNEY TIMES*/                    
int main()
{
//-------------------- DECLARE VARIABLES --------------------------------------//

          float departure_time, arrival_time;                                                              
          int departure_hours, departure_minutes;
          int arrival_hours, arrival_minutes;   
          int duration_hours, duration_minutes;

//---------------------- MAIN PROGRAM -----------------------------------------//

          printf("--- CALCULATIONS BASED ON A 24 HOUR CLOCK ---\n"); 
//Enter departure time
          printf("Enter the departure time of your train: ");
          scanf("%f", & departure_time);
          departure_hours = departure_time;     //Copy the float to an int to floor  its value

//Validate departure time based on a 24hr clock 
          while (departure_time - departure_hours > 0.59 || departure_time < 0 || departure_hours > 24 || (departure_hours == 24 && departure_time - departure_hours > 0))         
          {
                printf("Invalid. Re-enter the departure time of your train: ");
                scanf("%f", & departure_time);
                departure_hours = departure_time;            
          }      

          departure_minutes = (departure_time - departure_hours)*100;   //Multiply out remaining minutes so they can be stored as an integer    
 
//Enter arrival time              
          printf("Enter the arrival time of the train: ");
          scanf("%f", & arrival_time); 
          arrival_hours = arrival_time;
          
//Validate arrival time based on a 24hr clock 
          while (arrival_time - arrival_hours > 0.59 || arrival_time < 0 || arrival_hours > 24 || (arrival_hours == 24 && arrival_time - arrival_hours > 0))         
          {
                printf("Invalid. Re-enter the arrival time of your train: ");
                scanf("%f", & arrival_time);
                arrival_hours = arrival_time;            
          }             
          arrival_minutes = (arrival_time - arrival_hours)*100;

          duration_minutes = arrival_minutes - departure_minutes;

//Calculate journey time
          //If there is going to be a negative number of minutes
          if (duration_minutes < 0)
          {
                 duration_minutes = 60 + duration_minutes; //invert minutes on a range of 60 
                 arrival_hours = arrival_hours - 1;        //the journey will now take one less hour
          }
          duration_hours = arrival_hours - departure_hours;
          //If the journey travels through midnight
          if (duration_hours < 0)
                 duration_hours = 24 + duration_hours;     //invert hours on a scale of 24      
//Display journey time         
          printf("The journey will take %i hours and %i minutes", duration_hours, duration_minutes);          
          
                            
          getchar();
          getchar();
          return 0;
}

Also a friend of mine said that theres a way to turn a float input by scanf into two seperate integers. EG: 23.45 becomes 23 and 45. If its possible could someone let me know haw that would be done, it would have made this prog a bit simpler.

It would be considerably easier if you did
scanf( "%d.%d", &hours, &minutes );

From there, it's easy maths to calculate a minute value from both times.

Yes. That is better. I rewrit the prog, so it now looks like:

Code:

#include <stdio.h>
#include <conio.h>

                  /* MIKE GRUNDEL */
               /*TASK 5: JOURNEY TIMES*/                    
int hours, minutes;

int main()
{
          void INPUT_TIME();
//-------------------- DECLARE VARIABLES --------------------------------------//
                                                            
          int departure_hours, departure_minutes;
          int arrival_hours, arrival_minutes;   
          int duration_hours, duration_minutes;

//---------------------- MAIN PROGRAM -----------------------------------------//

          printf("--- CALCULATIONS BASED ON A 24 HOUR CLOCK ---\n"); 
//Enter departure time
          printf("Enter the departure time of your train: ");
          INPUT_TIME(departure_hours, departure_minutes);   
          departure_hours = hours;
          departure_minutes = minutes;
//Enter arrival time
          printf("Enter the arrival time of your train: ");
          INPUT_TIME(arrival_hours, arrival_minutes); 
          arrival_hours = hours;
          arrival_minutes = minutes;          
          
//Calculate journey time

          duration_hours = arrival_hours - departure_hours;
          duration_minutes = arrival_minutes - departure_minutes;

          //If there is going to be a negative number of minutes
          if (duration_minutes < 0)
          {
                 duration_minutes = 60 + duration_minutes; //invert minutes on a range of 60 
                 arrival_hours = arrival_hours - 1;        //the journey will now take one less hour
          }
          duration_hours = arrival_hours - departure_hours;
          //If the journey travels through midnight
          if (duration_hours < 0)
                 duration_hours = 24 + duration_hours;     //invert hours on a scale of 24      
//Display journey time         
          printf("The journey will take %i hours and %i minutes", duration_hours, duration_minutes);          
                          
          getchar();
          getchar();
          return 0;
}

//-----------------------FUNCTIONS----------------------------//
void INPUT_TIME()
{
          scanf("%i: %i", &hours, &minutes);
          while (minutes > 59 || minutes < 0 || hours > 24 || hours < 0 || (hours == 24 && minutes > 0))         
          {
                printf("Invalid. Re-enter the time: ");
                scanf("%i:%i", &hours, &minutes); 
          }           
}

One problem is that I dont know how to return variables from a void functon. I did it once before and I remember that you needed to use a * pointer thingy. It would be cool if someone could give me an example of how this program could be run without having to have "hours" and "minutes" as globals.

Another problem with this prog is if the time is not entered in HH:MM format, with the colon, the while loop for the validation runs infinitely. How could I stop that from happening?

It would be cool if someone could give me an example of how this program could be run without having to have "hours" and "minutes" as globals.

Pointer example:

Code:

#include <stdio.h>

void increment(int *x);

int main(void) {
    int x = 1;

    printf("%i\n", x);
    increment(&x);
    printf("%i\n", x);

    return 0;
}

void increment(int *x) {
    *x += 1;
}

/* output
1
2
*/

Another problem with this prog is if the time is not entered in HH:MM format, with the colon, the while loop for the validation runs infinitely. How could I stop that from happening?

If I may: http://board.theprogrammingsite.com/viewtopic.php?t=223

Thanks. Seems I forgot to include & when passing my parameters in o_0. The scanf thing will be useful.