Write a C program to check if two integers have opposite or same signs using bitwise operators

Two integers have opposite signs if their most significant bits (msb) are different. The most significant bit (also the sign bit for a signed integer) of any negative number will always be 1, on the contrary it will always be 0 if the number is positive. Following that, if bitwise operator exclusive OR (XOR "^") is applied on two integers of opposite signs, the resultant number will be a negative one. Because most significant bits of both numbers will not be the same and in that case XOR operation will produce 1 (as XOR operator results zero only when it is applied on 2 zeroes or 2 ones) that makes the resultant a negative number.

Hence, the result of bitwise exclusive OR applied on two integers will be less than zero, if numbers are of opposite signs.

Note that this solution of checking opposite signs of two numbers is for integers, because bitwise operators operate on char and int only.

C program to check whether two integer variables have same or different sings.

/* Write a C program to check if two integers have opposite signs. */
#include <stdio.h>
int main()
  int n1, n2; //declare two integers
  printf ("Enter two integer values: ");
  scanf ("%d%d", &n1, &n2);
  if ((n1 ^ n2) < 0)
    printf ("Both numbers (%d, and %d) have opposite signs.\n", n1, n2);
    printf ("Both numbers (%d, and %d) have same sign.\n", n1, n2);
  return 0;

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