I have to write a program that converts a number of minutes to days, hours, and minutes, converts days, hours, and minutes to minutes and computes the difference in two times in days, hours, and minutes format. I was given a drawing of the program on how it is supposed to work and from that i have written prototypes for the program. I have not seen any call-by-vaule or call by reference examples in tutorials so im kind of lost. do i need to #define days, minutes, and hours?
Code:
 
#include <stdio.h>
#include <math.h>
#define 

void displayMenu();
void needMenu(); 								// ask the user whether or not he/she wants
													// to display the menu
int makeSelection();							 // return a GOOD selection from the menu
													// i.e. error check the user entry
void processTask( int task ); 			// use a switch statement
													// to call one of the following
void processTask_1();
void processTask_2();
void processTask_3(); 						// convert both days, hours, mins to minutes
													// apply the absolute function to the difference
													// convert the difference minutes to
													// days, hours, mins
int getMinutes();
void getDhm ( int *days, int *hours, int *mins );
void min2dhm( int minutes, int *days, int *hours, int *mins );
int dhm2min( int days, int hours, int mins );

int main (void);
{
													//define variables
	double days;
	double hours;
	double minutes;

All i need is help getting started on these call-by-value and call-by-reference, preferable making sure i #define is correct and im headed in the right dir. thanks.
Thanks