C / C++ / MFC

int main(int argc, char* argv[])<br />
{<br />
	if (argc < 2)<br />
	{<br />
		printf ("Usage is: <CharFile> \n");<br />
		getchar();<br />
		return 1;<br />
	}<br />
	char * output = "";<br />
	char hash[5] = "abcd"; // Some Decoding hash<br />
	char * outputfile = "";<br />
	sprintf(outputfile,"%s.txt",argv[1]);<br />
	FILE * fp = fopen(argv[1],"r");<br />
	FILE * f = fopen(outputfile,"wt");<br />
<br />
	if (!fp)<br />
	{<br />
		printf ("Error opening file %s\n", argv[1]);<br />
		getchar();<br />
		return 2;<br />
	}<br />
	int findex = 0;<br />
	unsigned char d;<br />
	while (!feof(fp)) <br />
	{<br />
        int c = fgetc(fp);<br />
        if (c == EOF) break;<br />
        unsigned char k = (hash[findex % 4] + findex) % 256;<br />
        d = c ^ (k | 0x80);<br />
		findex++;<br />
		output += (char) d;<br />
		fprintf(f,(const char *) d);<br />
	}<br />
	fclose(fp);	<br />
	fclose(f);<br />
	return 0;<br />
}