Thread: Leap year program using if statements

I'm already half in the bag, but try something like below in lieu;

Code:

#include <iostream>
#include <stdlib.h>

int year;

int main()
{
	std::cout << "Enter a year and I will determine if it's a leap year:  " ;
	std::cin >> year ;
	
	int leap;
	leap = year % 4 ;

	if ( leap == 0 )
	{
		
				std::cout << "It is a leap year.";
				std::cin.get();
			 }
			else 
			{
				std::cout << "It is not a leap year.";
				std::cin.get();
			}

  
  system("PAUSE");	
  return 0;
}

Never heard of that. I thought a leap year was every 4, without exception. Who makes up these crazy rules?

Then;

Code:

#include <iostream>
#include <stdlib.h>



int main()
{
    int year;
	std::cout << "Enter a year and I will determine if it's a leap year:  " ;
	std::cin >> year ;
	
	int leap;
	int leap2;
	int leap3;
	leap = year % 4 ;
	leap2 = year % 100 ;
	leap3 = year % 400 ;

  if(leap2!=0)
   {
	if ( leap == 0 || leap3==0)
	{
		
				std::cout << "It is a leap year.";
				std::cin.get();
				std::cin.get();
			 }
			  }
			else 
			{
				std::cout << "It is not a leap year.";
				std::cin.get();
				std::cin.get();
			}
   	
  return 0;
}

Well, keep rearranging it until it works.

Code:

#include <iostream>
#include <stdlib.h>



int main()
{
    int year;
	std::cout << "Enter a year and I will determine if it's a leap year:  " ;
	std::cin >> year ;
	
	int leap;
	int leap2;
	int leap3;
	leap = year % 4 ;
	leap2 = year % 100 ;
	leap3 = year % 400 ;

	if (leap2!=0 && leap == 0 || leap3==0)
	{
				std::cout << "It is a leap year.";
				std::cin.get();
				std::cin.get();
			   }
			else 
			{
				std::cout << "It is not a leap year.";
				std::cin.get();
				std::cin.get();
			}

  return 0;
}

You shouldn't make all these variables global. There's no reason not to declare them in main(), directly before usage. Furthermore, the names leap, leap2 and leap3 are unintuitive. Given how short their initializers are, it's probably most readable to simply omit the variables and put the equivalent expressions directly where the usage is.

Also, your if-condition is messed up. It will tell you that every year divisible by 4 is a leap year. Consider:
leap == 0 -> divisble by 4. If this condition is true, the whole or-expression is true, and the second part is never evaluated.
If the condition is not true, then leap3 cannot be 0 either (there are no numbers divisble by 400 but not 4), and the entire expression is false.

You want to write, "if year is divisible by 4 and not by 100, or else if it is divisible by 400, then it's a leap year".

You should also always use parentheses to indicate precedence when mixing || and &&. && has higher precedence than ||, but (1) not all programmers know this, (2) it's not that way in all programming languages, and (3) it's easy to get wrong even if you actually know it.