This article will demonstrate a program to check if the input number is even or odd in python with example, output and explanation.

Even number
Integers which are divisible by 2 are called even numbers such as 2, 4, 42, 68, 1024 etc. These numbers when divided by 2 give a remainder 0.
Odd number
Integers which are not divisible by 2 are called odd numbers such as 3, 7, 9, 35, 87 etc. These numbers when divided by 2 give a remainder other than 0.

Algorithm
For checking if a number is odd or even, make use of modulus operator(`%`). Modulus operator divides two integers and returns the remainder of division.
Thus, if we use modulus operator with 2 and the number to check, it will give the remainder of division. Based on the remainder, we can easily determine if the number is even or odd using if-else statements.
Program
Python program to check odd or even number based on the above algorithm is given below.

```# read number from input
num = int(input("Enter a number\n"))

# compare remainder of division with 0
if num % 2 == 0:
print('Number is even')
else:
print('Number is odd')```

Explanation
The program reads an integer as input using `input()` function. Value read with `input()` function is in string format.
Since we have to perform arithmetic operations on this value, we need to convert it to an integer. This is done with `int()` function.

After this, we divide the number by 2 and compare the remainder with 0 using `==` operator. If the remainder is 0, the input number is even else it is odd. The result is printed on the screen.
Output of the program is

Enter a number
35
Number is odd

Enter a number
58
Number is even

Using function
You can place the logic to check if a number is even or odd in a function to make it reusable. The function shall accept the number to test as argument and return `True` or `False` based on the function name.
Below is a function to test even odd in python.

```def is_even(num):
# check f remainder is 0 and return result
return num % 2 == 0

num = int(input("Enter a number\n"))
# test with a function
if is_even(num):
print('Number is even')
else:
print('Number is odd')```

The function in this example accepts a number and returns `True` if the remainder after division by 2 is 0 or the number is even and `False` if the remainder is non-zero or the number is odd.
Based on the value returned by the function, we can output the result.

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