FAQ: How to test whether integer is even or odd

This is a discussion on FAQ: How to test whether integer is even or odd within the FAQ Board forums, part of the General Programming Boards category; Hi. I need to write a function that tests whether an integer is even or not. This is how far ...

  1. #1
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    Question FAQ: How to test whether integer is even or odd

    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.

    Code:
    /* 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.

  2. #2
    RoD
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    mod by two.

    variable = variable % 2;

  3. #3
    Code Goddess Prelude's Avatar
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    Code:
    #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
    My best code is written with the delete key.

  4. #4
    Programming Sex-God Polymorphic OOP's Avatar
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    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

  5. #5
    RoD
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    hmm, both seem about the same imo, i had only ever learned the modulous way of doing it.

  6. #6
    Programming Sex-God Polymorphic OOP's Avatar
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    Bitwise operations are faster than division, multiplication, addition, subtraction because it's just a quick check on the bits.

  7. #7
    RoD
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    thnx for the knowledge.

  8. #8
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    I tried the following:

    Code:
    /* 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:

    Code:
    Enter a number: 10
    10 is even
    98476
    Why is 98476 generated?
    Also, Polymorphic OOP, how would I implement Value & 1 ?

  9. #9
    Programming Sex-God Polymorphic OOP's Avatar
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    It's result is 1 if it's odd and 0 if it's even

    so

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

  10. #10
    Programming Sex-God Polymorphic OOP's Avatar
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    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:

    Code:
    /* 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;
    }

  11. #11
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    Originally posted by giggsy
    I tried the following:

    Code:
    /* 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:

    Code:
    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.

  12. #12
    Skunkmeister Stoned_Coder's Avatar
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    Code:
    const char* EvenOrOdd( int value)
    {
         if(value&1) return"odd";
         return "even";
    }
    Free the weed!! Class B to class C is not good enough!!
    And the FAQ is here :- http://faq.cprogramming.com/cgi-bin/smartfaq.cgi

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