C program, array read | CS 240 | Purdue University


Given two binary vectors X = (x1, x2, …, xN) and Y = (y1, y2, …, yN), each a 1-D array of N binary numbers, the number of positions where corresponding bit values of the two vectors are different is called the Hamming distance of the two vectors. For example, if X = (1,1,0,0) and Y = (1,0,0,1) then their Hamming distance is 2 since X and Y differ in their second and fourth positions counting from left to right. The Hamming distance is a useful tool in various subfields of computer science including communication networks where it captures how much two binary vectors differ. In the above example, X = (1,1,0,0) may comprise four bits transmitted by a sender whereas Y = (1,0,0,1) are the actual bits received by a receiver. The Hamming distance, d(X,Y) = 2, indicates that two bits of X flipped — i.e., changed their value from 0 to 1, or 1 to 0 — while traveling from sender to receiver. This is common when sending bits wirelessly using a smartphone or laptop over cellular and WiFi interfaces.

Write an app, calchamming, that takes as input two vectors whose components are binary from stdin, calculates their Hamming distance, and outputs the value to stdout. The format of the input should be

x1 x2 … xN
y1 y2 … yN

where N is an integer specifying the size of the 1-D arrays (i.e., dimension of 1-D vector), x1 x2 … xN are the N bit values of the first vector, and y1 y2 … yN are the bit values of the second vector. The individual bit values x1 x2 … xN are separated by a single space. The same holds for y1 y2 … yN. Assume that N cannot be greater than 15. Declare N, X[15], Y[15] to be local variables of main() of type int.

Perform reading of the input from a function

int readinput(int *, int *, int *);

where the first argument is a pointer to N, the second and third arguments point to the two 1-D arrays X and Y. readinput() returns 0 if successful, -1 if there is an error. For example, if N exceeds 15 then readinput() returns -1. Consider other cases that readinput() should consider as invalid input and return -1 to its caller main(). main() checks the return value of readinput() and terminates the app by calling exit(1) if it is -1. Perform calculation of the dot product by calling function

int calchamm(int, int *, int *);

where the first argument is the value of N, and the second and third arguments are pointers to the two arrays. calchamm() computes the Hamming distance of the binary vectors and returns the value to the caller main(). Since readinput() is tasked with checking that the input is valid, calchamm() can focus on performing the Hamming distance calculation. Print the Hamming distance to stdout by calling

void writeoutput(int);

where the int argument is the distance value.