Problem of the Day
A new programming or logic puzzle every Mon-Fri

The premise of this problem sounds easy. Write a function that returns if a number is negative or not. The tricky part comes from detecting -0. Your experience may vary be language. You'll also note that IEEE says that -0 === +0. Make sure your function can tell the difference.

Comments:

• Jason - 9 years, 10 months ago

  // JavaScript uses the IEEE 754 standard, so 1/-0 = -Infinity
  function isNegative0(x) {
    return x === 0 && (1/x) === -Infinity;
  }
  
  console.log("+0:",isNegative0(+0)); // false
  console.log("-0:",isNegative0(-0)); // true
  

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• Jason - 9 years, 10 months ago

  Wow... I should read the whole problem.... here is the correct one

  // JavaScript uses the IEEE 754 standard, so 1/-0 = -Infinity
  function isNegative(x) {
    return x < 0 || (x === 0 && (1/x) === -Infinity);
  }
  
  console.log("+1:",isNegative(+1)); // false
  console.log("+0:",isNegative(+0)); // false
  console.log("-0:",isNegative(-0)); // true
  console.log("-1:",isNegative(-1)); // true
  

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• Jason - 9 years, 10 months ago

  main :: IO ()
  main = do
      print $ isNegative (1 :: Double) -- False
      print $ isNegative (0 :: Double) -- False
      print $ isNegative (-0 :: Double) -- True
      print $ isNegative (-1 :: Double) -- True
  
  isNegative :: RealFloat a => a -> Bool
  isNegative x
      | x < 0 = True
      | isNegativeZero x = True -- Haskell has isNegativeZero defined for RealFloat in Prelude
      | otherwise = False
  

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