Even or odd program C program to check odd or even: We will determine whether a number is odd or even by using different methods all are provided with a C language program. As you have studied in Mathematics that in decimal number system even numbers are divisible by two while odd numbers are not so we can use modulus operator(%) which returns remainder, For example, 4%3 gives 1 (remainder when four is divided by three). Even numbers are of the form 2*n, and odd numbers are of the form (2*n+1) where n is is an integer.