C++ validating date without using class - c++

Question

Hi I am hoping someone can help me out with what I am doing wrong. This is homework I will point out but was in need of someone to tell me what a moron I am because I am not seeing what it is that I am doing wrong.
I am supposed to let the user enter a month, day, and year to determine if it is a magic date. That part I had already done for another project. I am supposed to go back and validate the date using a function named isDateValid. I'm pretty sure I am missing something obvious and could use anyones help on the subject. Thanks!
The problem is when I run it I am always getting that it is an invalid date!
#include <iostream>
using namespace std;
bool leapYear(int);
bool isDateValid(int, int, int);
int main()
{
int month, day, year;
cout << "Is the date you are thinking of a magic one? Let's see...\n";
cout << "What is the month in numeric form only? "; cin >> month;
cout << "What is the day of the month? "; cin >> day;
cout << "What is the four digit year? "; cin >> year;
if (isDateValid(month, day, year) == false)
{
cout << "The date you entered, "<< month << "/" << day << "/" <<
year << " is NOT a VALID Date.\n";
cout << "If you think I am wrong, please feel free to run me again";
}
else if (month * day == year % 100) // if true then do this
{
cout << "The date you entered, " <<
month << "/" << day << "/" << year << " is a magic date!!\n";
}
else // if false then do this
{
cout << "The date you entered, " << month << "/" << day << "/" <<
year << " is NOT a magic date!!\n";
}
//Program ID
cout <<"\n" << "L5P1LB.cpp\n" << "11-26-12\n" << endl;
system ("pause");
return 0;
}//end main
// isDateValid function to validate date entered
bool isDateValid(int month, int day, int year)
{
bool validation = true;
if(!(year >= 1600 && year <=2100))
validation = false;
if(leapYear(year))
{
if ((month == 2) && (day > 29))
validation = false;
}
else if(!leapYear(year))
{
if ((month == 2) && (day > 28))
validation = false;
}
if((month < 1 && month > 12) || (day < 1))
validation = false;
if((month == 1) || (month ==3) || (month == 5) || (month == 7) ||
(month == 8) || (month == 10) || (month == 12) && (day > 31))
validation = false;
else if (((month == 4) || (month == 6) || (month == 9) || (month == 11)) &&
(day > 30))
validation = false;
else
validation == true;
return validation;
}
// leapYear function to determine if the year is a leap year for validation
bool leapYear(int year)
{
return(year % 100 != 0 && year % 4 == 0) || (year % 400 == 0);
} // end leapYear
EDIT
Okay now my problem is that I am not getting that it is NOT A valid date when it is. Its skipping the validation all together and just running the "magic date" part of it!
Here's the rewrite plus my full code hopefully indented here properly as it is in Bloodshed.
Description: This program determines if when the user enters a month,
day, and four digit year which will then be stripped down to its
two digit year and determined to be a magic date if the day entered
multiplied by the month entered equals the years two digit format.
Design:
begin main
input data
Ask user for a month in number form
Ask user for a day of the month
Ask user for four digit month
Validate
begin isDateValid
if year is between 1600 and 2100, inclusive then return
true
if month is between 1 and 12, inclusive return true
if month is Jan, Mar, May, July, Aug, Oct, Dec
then if day is between 1 and 31 inclusive return true
if month is Apr, June, Sept, Nov
then if day is between 1 and 30 inclusive return true
if month is Feb
then determine if leap year by running function
leapYear provided for us.
if leap year is true
then if day is between 1 and 29, inclusive return true
if not leap year then if day is between 1 and 28,
inclusive then return true
end isDateValid
if isDateValid is true then
Calculate
if the month times the year is equal to the year modulus 100
then output it is a magic date
if it does not equal the year in 2 digit form
then output that it is not a magic date
else output error message
Output Program ID
end main
The output needs to include the books data of 6/10/1960 */
#include <iostream>
using namespace std;
bool leapYear(int);
bool isDateValid(int, int, int);
int main()
{
int month, day, year;
cout << "Is the date you are thinking of a magic one? Let's see...\n";
cout << "What is the month in numeric form only? "; cin >> month;
cout << "What is the day of the month? "; cin >> day;
cout << "What is the four digit year? "; cin >> year;
if (isDateValid(month, day, year) == false)
{
cout << "The date you entered, "<< month << "/" << day << "/" <<
year << " is NOT a VALID Date.\n";
cout << "If you think I am wrong, please feel free to run me again";
}
else if (month * day == year % 100) // if true then do this
{
cout << "The date you entered, " <<
month << "/" << day << "/" << year << " is a magic date!!\n";
}
else // if false then do this
{
cout << "The date you entered, " << month << "/" << day << "/" <<
year << " is NOT a magic date!!\n";
}
//Program ID
cout <<"\n" << "L5P1LB.cpp\n" << "11-26-12\n" << endl;
system ("pause");
return 0;
} //end main
// isDateValid function to validate date entered
bool isDateValid(int month, int day, int year)
{
bool validation = true; // validation set to true
// if it is not between 1600 and 2100 then set to false
if(!(year >= 1600 && year <=2100))
validation = false;
// call leapYear function
if(leapYear(year))
{
// if February and day is greater than 29 then set to false
if ((month == 2) && (day > 29))
validation = false;
}
// else if NOT leapYear
else if(!leapYear(year))
{
// if February and day is greater then 28 then set to false
if ((month == 2) && (day > 28))
validation = false;
}
// if month is less then 1 and over 12 then set to false
if((month < 1 && month > 12))
validation = false;
// if day is less then 1 then set to false
if(day < 1)
validation = false;
// if month is 1 (Jan), 3 (Mar), 5 (May), 7 (July), 8 (Aug), 10 (Oct),
// or 12 (Dec) and day is greater then 31 set to false
if((month == 1) || (month ==3) || (month == 5) || (month == 7) ||
(month == 8) || (month == 10) || (month == 12) && (day > 31))
validation = false;
// if month is 4 (Apr), 6 (June), 9 (Sept), or 11 (Nov) and day is
// greater then 30 set to false
if (((month == 4) || (month == 6) || (month == 9) || (month == 11)) &&
(day > 30))
validation = false;
// else everything that is left set validation to true
else
validation = true;
return validation;
} // End isDateValid
// leapYear function to determine if the year is a leap year for validation
bool leapYear(int year)
{
return(year % 100 != 0 && year % 4 == 0) || (year % 400 == 0);
} // end leapYear
Sorry if I put in the wrong spot or anything!
Thanks for your help also. It is truly appreciated.

Answer 1

You had a few mistakes in your date validation.
The operator precedence noted by Luchian is one, but you had a few others:
You test that month < 1 && month > 12 - this is impossible, a month cannot be smaller than 1 and greater than 12
validation == true doesn't do anything. == is a comparison operator. Luckily this didn't affect your function as validation was already true when reaching this code.
I took the liberty to rewrite it in what I think is a cleaner fashion, but you could probably just fix the month check if you prefer to keep your version
bool isDateValid(int month, int day, int year)
{
bool validation = true;
if(!(year >= 1600 && year <=2100))
validation = false;
if(day < 1)
validation = false;
switch(month)
{
case 2:
if(leapYear(year)) // We only care about leap years in February
if(day > 29)
validation = false;
else
if(day > 28)
validation = false;
break;
case 1: case 3: case 5: case 7: case 8: case 10: case 12:
if(day > 31)
validation = false;
break;
case 4: case 6: case 9: case 11:
if(day > 30)
validation = false;
break;
default: // the month is not between 1 and 12
validation = false;
break;
}
return validation;
}

Answer 2

|| is short-circuiting, so (month == 1) || (month ==3) || (month == 5) || (month == 7) ||
(month == 8) || (month == 10) || (month == 12) && (day > 31) evaluates to true if the first conditions are met. You need to add an extra set of parenthesis:
((month == 1) || (month ==3) || (month == 5) || (month == 7) ||
(month == 8) || (month == 10) || (month == 12)) && (day > 31)
Same for the other months.
Also,
validation == true;
is a no-op, you probably meant validation = true.

Answer 3

Personally, I'd suggest something more direct and concise. The ? ternary operator can be a little confusing at first, but is very simple once clearly understood. I think of it as a kind of "if-else" that can be embedded in expressions.
bool isDateValid(int month, int day, int year)
{
return year >= 1600 && year<= 2100 &&
month >= 1 && month <= 12 &&
day >= 1 &&
day <= (month == 2 ? (leapyear(year) ? 29 : 28) :
month == 9 || month == 4 || month == 6 || month == 11 ? 30 : 31);
// "30 days has September, April, June and November..."
}
It may be a little more readable if you use an enum for month constants:
enum Month { Jan = 1, Feb, Mar, Apr ... };
Aim being to actually code:
day <= (month == Feb ? ...