#include <stdio.h>

int main(int argc, char **argv) {
    if (argc < 2) {
        fprintf(stderr, "Usage: xor [FILE]...\nAll files XORed to stdout, size: minimum of all.\n");
	return(1);
    }
    int nbFiles = argc-1;
    FILE *files[nbFiles];
    bool errors = false;
    for (int i=0;i<nbFiles;i++) {
	files[i] = fopen(argv[i+1], "r");
    	if (files[i] == NULL) {
       	    fprintf(stderr, "Could not open '%s'.\n", argv[i+1]);
            errors = true;
	}
    }
    if (errors) return(1);
    char c[argc-1];
    do {
	int cc;
        for (int i=0;i<nbFiles;i++) {
	    cc = fgetc(files[i]);
	    if (cc == EOF) break;
	    c[i] = (char)cc;
	}
	if (cc == EOF) break;
	char xored = '\0';
	for (int i=0;i<nbFiles;i++) xored ^= c[i];
        printf("%c", xored);
    } while(1);
}