Here is an example of a C program that checks if a number is even or odd:

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#include <stdio.h> int main() {    int num;    printf("Enter an integer: ");    scanf("%d", &num);    if (num % 2 == 0) {        printf("%d is even.", num);    } else {        printf("%d is odd.", num);    }    return 0; }

The program prompts the user to enter an integer, which is stored in the variable "num". The modulus operator (%), which returns the remainder of a division operation, is used to check if the number is even or odd. If the remainder when "num" is divided by 2 is 0, the number is even. If the remainder is not 0, the number is odd. The program then prints out a message indicating whether the number is even or odd.

You can also use bitwise operator instead of modulus operator to check if a number is even or odd:

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if (num & 1 == 0) {    printf("%d is even.", num); } else {    printf("%d is odd.", num); }

Here the bitwise operator & will perform a bit-by-bit 'AND' operation. If the last bit of the number is 0 then the number is even otherwise it's odd.