FAQ: How to test whether integer is even or odd

[giggsy]

Hi. I need to write a function that tests whether an integer is even or not. This is how far I've got. I wasn't sure if its best to use an 'if' statement in the function.

/* a function that tests whether an integer is even, returning a true or false
   answer */

#include <iostream>

using namespace std;

int main()
{
  int n = 0;

  cout << "Enter a number: ";
  cin >> n;

  cout << test(n) << endl;

  return 0;
}

int test(int n)
{
  if (n

cheers.

[RoD]

mod by two.

variable = variable % 2;

[Prelude]

#include <iostream>

int main()
{
  int val;

  std::cout<<"Enter a number: ";
  std::cin>> val;

  if ( val % 2 == 0 )
    std::cout<< val <<" is even"<<std::endl;
  else
    std::cout<< val <<" is odd"<<std::endl;
}

-Prelude

[Polymorphic OOP]

Or, if you want to optimize just do:

Value & 1

if the result of the expression is true then the number was odd, if false, then the number was even

[RoD]

hmm, both seem about the same imo, i had only ever learned the modulous way of doing it.

[Polymorphic OOP]

Bitwise operations are faster than division, multiplication, addition, subtraction because it's just a quick check on the bits.

[RoD]

thnx for the knowledge.

[giggsy]

I tried the following:

/* a function that tests whether an integer is even, returning a true or false
   answer */

#include <iostream>

using namespace std;

int evenTest(int);

int main()
{
  int n = 0;

  cout << "Enter a number: ";
  cin >> n;

  cout << evenTest(n) << endl;

  return 0;
}

int evenTest(int n)
{
  if (n % 2 == 0)
    cout << n << " is even" << endl;
else
    cout << n << " is odd" << endl;
}

It generates the following output:

Enter a number: 10
10 is even
98476

Why is 98476 generated?
Also, Polymorphic OOP, how would I implement Value & 1 ?

[Polymorphic OOP]

It's result is 1 if it's odd and 0 if it's even

so

std::cout << "Value is " << ( Value & 1 ? "odd" : "even" );

[Polymorphic OOP]

Originally posted by giggsy
Why is 98476 generated?

Because you are "cout"ing the value that evenTest returns (which is garbage cuz you didn't return anything.

What you should do is:

/* a function that tests whether an integer is even, returning a true or false
   answer */

#include <iostream>

using namespace std;

bool evenTest(int);

int main()
{
  int n = 0;

  cout << "Enter a number: ";
  cin >> n;

  cout << n << " is " << ( evenTest(n) ? "even" : "odd" ) << endl;

  return 0;
}

inline bool evenTest(int n)
{
 return n % 2 == 0;
}

[Eibro]

Originally posted by giggsy
I tried the following:

/* a function that tests whether an integer is even, returning a true or false
   answer */

#include <iostream>

using namespace std;

int evenTest(int);

int main()
{
  int n = 0;

  cout << "Enter a number: ";
  cin >> n;

  cout << evenTest(n) << endl;

  return 0;
}

int evenTest(int n)
{
  if (n % 2 == 0)
    cout << n << " is even" << endl;
else
    cout << n << " is odd" << endl;
}

It generates the following output:

Enter a number: 10
10 is even
98476

Why is 98476 generated?
Also, Polymorphic OOP, how would I implement Value & 1 ?

That random number is generated because you're printing the result of a function which is supposed to return an int, but actually returns nothing.

[Stoned_Coder]

const char* EvenOrOdd( int value)
{
     if(value&1) return"odd";
     return "even";
}