Let n be a number
    n &1 = 0000000d where d is the LSB of n 
    So, 
    If LSB ==1
        It's odd number
    Else
        Even no

To understand the concept of "LSB" & bitwise operators please read: Bitwise Operators and their working with Examples in C

Example:

    Let n be 7 //00000111
    n & 1 = 1 
    00000111(7) & 00000001(1) =00000001 (1)
    Thus it's an odd number
    Let n be 6 //00000110
    N&1=0
    00000110(6) & 00000001(1) =00000000 (0)
    Thus it's an even number

C implementation

#include <stdio.h>

int main()
{
	int n;

	printf("enter no: ");

	scanf("%d",&n);

	//n&1 actually results in 0000000d where d is your LSB
	if(n&1==1)
		printf("it's odd no");//for odd no LSB 1
	else
		printf("it's even no");//for even no LSB 0

	return 0;
}

Output

First run:
enter no: 7
it's odd no

Second run:
enter no: 6
it's even no