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Asney
Asked: 2020-12-15 05:24:36 +0800 CST 2020-12-15 05:24:36 +0800 CST

How to detect parity of a number without the % operator?

  • 772

I have a variable that the server gives me with a value, I need to know if the number is even or odd , but without using %2:

$.ajax({ 
    url:'/numero',
    type:'POST',
    success:function(num){
       // ¿Qué hago con num para saber qué es?
       // num.numero me da el valor del numero ej;5,7,2...
    }

})
javascript

5 Answers

  1. Best Answer

    It's very simple: use the AND bitwise operator .

    In binary, even numbers have the last bit set to 0 , while odd numbers have the last bit set to 1 :

    1512 & 1 ==> 0 (it's even)
    1511 & 1 ==> 1 (it's odd)

    Therefore:

    function espar( x ) {
  return !( x & 1 );
}
console.log(espar(1512));
console.log(espar(1511));

    spread( 1512 ) ==> true
    spread( 1511 ) ==> false

    I can't resist the moral : there are only 10kinds of people: those who know binary and those who don't ;-)

    • 41

  2. Divide the number by 2. Odd numbers will always return a decimal number while even numbers will not. Then it would only be necessary to verify if it is a decimal by converting the result to a string and search for the point:

    var value = prompt("Ingrese numero:");

var esPar = (parseInt(value)/2).toString().indexOf('.')==-1;

if(esPar){
  console.log("el numero es par");
}
else{
  console.log("el numero es impar");
}

    • 5

  3. Why don't you just do a division math operation? If when dividing a number by 2 the result of the division is exact, it means that the number is even, so we validate this with a regular expression, it is simply asking "if the result of the division contains a point, it means that it was not exact and that therefore Therefore the number is odd.

    $("#preguntar").click(function(){
  var numero = $("#numero").val();
  
  var division = (Number(numero) / 2);
  var expresion = new RegExp(/\./);
  
  if(expresion.test(division.toString())){
    console.log('El número ingresado es impar');
  }else{
    console.log('El número ingresado es par');
  }
})
    <script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>

<input type="text" id="numero">

<button id="preguntar">Par o impar</button>

    • 4

  4. Knowing the last digit of your number you can decipher if the whole number is even or odd since it is known that the numbers ending in 0,2,4,6 and 8 are even, therefore

    You can do the following:

    $.ajax({ 
    url:'/numero',
    type:'POST',
    success:function(num){
       //Declaro todos los numeros en los que debe terminar los #s pares
       var pars = [0,2,4,6,8];
       //Verifico si el numero actual termina en uno de esos y asi veo cuando es par y cuando no
       if(pars.indexOf(parseInt(num.toString().charAt(num.toString().length-1))) >= 0)
          console.log("es par");
        else 
          console.log("es impar");
    }

});
    • 0

  5. //find if a number is even or odd without using modulus

    const parImpar = (n) => {

   return n === 0 ? console.log(`El numero ${n} no es divisible` ) : String(n/2).includes('.') === true ? console.log('el numero es impar'): console.log('el numero es par')

 }

parImpar(5)```
    • 0