A small, slightly hacky C program to calculate the parity of data and then compare it using modified data. This will probably be used for some sort of homework assignment.

calculateParity.c

#include <stdio.h>

//Code for calculate parity from http://graphics.stanford.edu/~seander/bithacks.html#ParityNaive
unsigned int calculateParity(int data) {
	unsigned int parity = 1; //Even parity to start
	while (data) {
	  parity = !parity;
	  data = data & (data - 1);
	}
	return parity;
}

//Make sure to understand why I change the data I do. I would change it to your own. It isn't too hard
int main(void) {
	unsigned int originalData = 0xDE;       // word value to compute the parity of
	unsigned int parity = calculateParity(originalData);
	
	printf("%s: %#02x\n", "Original Data", originalData);
	printf("%s: %d\n", "Parity Bit", parity);
	//Add parity bit
	unsigned int parityData = originalData << 1;
	parityData = parityData | parity;
	//Do parity checks
	int result;
	int parityBit = parityData & 1;
	result = parityBit == calculateParity(originalData);
	printf("%s (%#02x): %d\n", "Original Data OK", originalData, result);
	//Modify the data to make it bad and do the parity check again (1 bit)
	originalData = originalData + 1;
	result = parityBit == calculateParity(originalData);
	printf("%s (%#02x): %d\n", "1 bit error OK", originalData, result);
	//2 bit
	originalData = 0xFF;
	result = parityBit == calculateParity(originalData);
	printf("%s (%#02x): %d\n", "2 bit error OK", originalData, result);
	//3 bit
	originalData = 0xFD;
	result = parityBit == calculateParity(originalData);
	printf("%s (%#02x): %d\n", "3 bit error OK", originalData, result);
	return 0;
}