Check if a number is positive, negative or zero using bit operators

Given a number N, check if it is positive, negative or zero without using conditional statements.

Examples:

Input : 30
Output : 30 is positive

Input : -20
Output : -20 is negative

Input: 0
Output: 0 is zero



The signed shift n>>31 converts every negative number into -1 and every other into 0.
When we do a -n>>31, if it is a positive number then it will return -1 as we are doing -n>>31 and the vice versa when we do for a negative number.
But when we do for 0 then n>>31 and -n>>31 both returns 0, so we get a formula:

1 + (n>>31) – (-n>>31)

..1) when n is negative :
1 +(-1)-0=0

..2) when n is positive:
1+0-(-1)=2

..3) when n is 0:
1+0-0=1

So we know it returns 0 when it is a negative number, it returns 1 when it is zero, returns 2 when it is a positive number.

So to not use if statements we store at 0th index “negative”, 1st index “zero” and at 2nd index “positive”, and print according to it.

CPP

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// CPP program to find if a number is
// positive, negative or zero using
// bit wise operators.
#include <iostream>
using namespace std;
  
// function to return 1 if it is zero
// returns 0 if it is negative
// returns 2 if it is positive
int index(int i)
{
    return 1 + (i >> 31) - (-i >> 31);
}
  
void check(int n)
{
    // string array to store all kinds of number
    string s[] = { "negative", "zero", "positive" };
  
    // function call to check the sign of number
    int val = index(n);
  
    cout << n << " is " << s[val] << endl;
}
  
// driver program to test the above function
int main()
{
    check(30);
    check(-20);
    check(0);
    return 0;
}

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Java

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// Java program to find if a number is
// positive, negative or zero using
// bit wise operators.
class GFG {
      
    // function to return 1 if it is zero
    // returns 0 if it is negative
    // returns 2 if it is positive
    static int index(int i)
    {
        return 1 + (i >> 31) - (-i >> 31);
    }
  
    static void check(int n)
    {
          
        // string array to store all kinds
        // of number
        String s[] = { "negative", "zero"
                              "positive" };
  
        // function call to check the sign 
        // of number
        int val = index(n);
  
        System.out.println(n + " is " + s[val]);
    }
      
    // Driver code
    public static void main(String[] args)
    {
        check(30);
        check(-20);
        check(0);
    }
}
  
// This code is contributed by Anant Agarwal.

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Python3

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# Python 3 program to
# find if a number is
# positive, negative
# or zero using
# bit wise operators.
  
# function to return 1 if it is zero
# returns 0 if it is negative
# returns 2 if it is positive
def index(i):
  
    return 1 + (i >> 31) - (-i >> 31)
  
  
def check(n):
  
    # string array to store all kinds of number
    s = "negative", "zero", "positive"
  
    # function call to check the sign of number
    val = index(n)
  
    print(n,"is",s[val])
  
  
# driver program to
# test the above function
check(30)
check(-20)
check(0)
      
# This code is contributed by
# Smitha Dinesh Semwal

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C#

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// C# program to find if a number is
// positive, negative or zero using
// bit wise operators.
using System;
  
class GFG {
      
    // function to return 1 if it is zero
    // returns 0 if it is negative
    // returns 2 if it is positive
    static int index(int i)
    {
        return 1 + (i >> 31) - (-i >> 31);
    }
       
    static void check(int n)
    {
          
        // string array to store all kinds of number
        String []s = { "negative", "zero", "positive" };
       
        // function call to check the sign of number
        int val = index(n);
       
        Console.WriteLine(n + " is " + s[val]);
    }
      
    //Driver code
    public static void Main()
    {
        check(30);
        check(-20);
        check(0);
    }
}
  
// This code is contributed by Anant Agarwal.

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PHP

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<?php
// PHP program to find if a number is
// positive, negative or zero using
// bit wise operators.
  
// function to return 1 if it is zero
// returns 0 if it is negative
// returns 2 if it is positive
function index($i)
{
    return 1 + ($i >> 31) - 
               (-$i >> 31);
}
  
function check($n)
{
      
    // string array to store
    // all kinds of number
    $s = array("negative", "zero", "positive" );
  
    // function call to check 
    // the sign of number
    $val = index($n);
  
    echo $n, " is ", $s[$val], "\n";
}
  
    // Driver Code
    check(30);
    check(-20);
    check(0);
  
// This code is contributed by Ajit
?>

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Output:

30 is positive
-20 is negative
0 is zero


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Striver(underscore)79 at Codechef and codeforces D

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