Mathematics 1201: Programming in C
	       Solutions to Reading and Homework Assignment #4
			     Prof. Wickerhauser

Chapter 4 Exercises:

Exercise 9, p.100
  Program:
    int
    IsLeap( int Year )
    {
      if( Year % 4 == 0 )		/* divisible by 4... */
	if( Year % 100 != 0		/* ...and not divisible by 100... */
	   || Year % 400 == 0 )	/* ...unless also divisible by 400 */
	  return 1;			/* Leap Year! */
      return 0;			/* Not a leap year. */
    }


Exercise 10, p.101
  Program:
    #define FAIL	return 0
    #define SUCCEED	return 1
    #define JAN 1
    #define FEB 2
    #define MAR 3
    #define APR 4
    #define MAY 5
    #define JUN 6
    #define JUL 7
    #define AUG 8
    #define SEP 9
    #define OCT 10
    #define NOV 11
    #define DEC 12
    int IsLeap ( int Year );	/* Prototype of Exercise 9 function */

    int
    DaysIn( int Month, int Year )
    {
      switch(Month) {
      case JAN: case MAR: case MAY: case JUL: case AUG: case OCT: case DEC:
	return 31;
      case APR: case JUN: case SEP: case NOV:
	return 30;
	break;
      case FEB:
	if( IsLeap(Year) ) return 29;
	else return 28;
      }
      return -1;			/* Month is not 1,2,...,12 */
    }

    int
    IsActualDate( int Month, int Day, int Year )
    {
      /* Test for problems; quit and return 0 at the first one */
      if( Year<1600 || Year>2500 ) FAIL;
      if( Month<1 || Month>12 ) FAIL; /* not actually necessary */
      if( Day<1 || Day>DaysIn( Month, Year) ) FAIL;
      SUCCEED;
    }


Exercise 11, p.101
  Program:
    int IsLeap ( int Year );	/* Prototype of Exercise 9 function */
    int DaysIn( int Month, int Year ); /* Prototype of Ex. 10 function #1 */
    int IsActualDate( int Month, int Day, int Year ); /* Ex. 10 function #2 */

    int
    ElapsedDays( int Month, int Day, int Year )
    {
      /* Time in days since Dec 31, 1599 */
      int y, m, days;

      if ( !IsActualDate(Month, Day, Year) )
	return -1;		/* indicates unreasonable inputs */
      days = Day;		/* count the excess days */
      for( m=1; m<Month; m++ )	/* count the days in the excess months */
	days += DaysIn(m,Year);
      for( y=1600; y<Year; y++ ) /* count the days in the excess years */
	if ( IsLeap(y) )	days += 366;
	else		days += 365;
      return days;
    }



Exercise 12, p.101
  Program:
    #include <stdio.h>
    int IsLeap ( int Year );	/* Prototype of Exercise 9 function */
    int DaysIn( int Month, int Year ); /* Prototype of Ex. 10 function #1 */
    int IsActualDate( int Month, int Day, int Year ); /* Ex. 10 function #2 */
    int ElapsedDays( int Month, int Day, int Year ); /* Ex. 11 function */

    #define COMPLAIN  {printf("Date is out of range.\n"); return 1;}
    int
    main( void )
    {
      /* Time in days between two dates since Dec 31, 1599 */
      int d1, m1, y1, d2, m2, y2, ed1, ed2;

      /* Prompt for two dates: */
      printf("Enter the first date like `mm dd yyyy': ");
      scanf( "%d %d %d", &m1, &d1, &y1 );
      ed1 = ElapsedDays(m1, d1, y1 ); /* returns -1 on bad inputs */
      if ( ed1<0 ) COMPLAIN;

      printf("Enter the second date like `mm dd yyyy': ");
      scanf( "%d %d %d", &m2, &d2, &y2 );
      ed2 = ElapsedDays(m2, d2, y2 ); /* returns -1 on bad inputs */
      if ( ed2<0 ) COMPLAIN;

      if( ed1==ed2 )
	printf("The two dates are identical.\n");
      else
	if( ed1<ed2)
	  printf("First date preceeds second by %d days.\n", ed2-ed1);
	else /* ed1>ed2 */
	  printf("First date follows second by %d days.\n", ed1-ed2);

      return 0;
    }