// $Id: cmp_string.c,v 1.2 2009/09/08 01:44:01 joe Exp joe $
// eecs337 homework #1
// Joe Teagno (jrt32)

#include <stdio.h>
#include <string.h>
#include <assert.h>

int main(int argc, char* argv[])
{
	// we'll pack up our strings to make it easier to work with them
	typedef struct {
		char* a; // pointer to the first character of string a
		char* b; // likewise for string b
	} string_pair;

	// put the string pairs into an array so we can easily loop through them
	int string_pairs_length = 4;
	string_pair string_pairs[string_pairs_length];

	string_pairs[0].a = "eecs";
	string_pairs[0].b = "eecs";

	string_pairs[1].a = "eecs";
	string_pairs[1].b = "EECS";

	string_pairs[2].a = "eecs";
	string_pairs[2].b = "eec";

	string_pairs[3].a = "eecs";
	string_pairs[3].b = NULL;

	// notice that I'm declaring int i here, outside of the for loop.
	// when I try to declare i inside the for loop (as in "for (int i=0; ...")
	// gcc complains "error: ‘for’ loop initial declaration used outside C99 mode"
	// I don't know if this means that I'm not allowed to do this in C at all
	// (doubtful), or whether this construct wasn't made legal until
	// some later revision of C ("C99"?), and that I would need to set some
	// switch in gcc in order to allow it.
	int i;
	for (i=0; i<string_pairs_length; i++)
	{
		// get pointers to the first characters of our strings
		char* char_ptr_a = string_pairs[i].a;
		char* char_ptr_b = string_pairs[i].b;

		// cast the pointers-to-string as pointers-to-void
		void* void_ptr_a = (void*) char_ptr_a;
		void* void_ptr_b = (void*) char_ptr_b;

		// printf-- like the rest of the standard string function-- expects pointers-to-char
		printf("comparison of \"%s\" and \"%s\": ", char_ptr_a, char_ptr_b);

		// use our nifty comparsion-- it expects pointers-to-void
		int result = cmp_string(void_ptr_a, void_ptr_b);

		printf("%d\n", result);

	} // end for i
}

// this is our own string-comparison function.
// unlike the standard library's function, it expects pointers-to-void
int cmp_string(const void* a, const void* b)
{
	// cast the pointers-to-void back into pointers-to-char
	char* char_ptr_a = (char*) a;
	char* char_ptr_b = (char*) b;

	// make sure that neither of the string arguments are null pointers
	assert((char_ptr_a != NULL));
	assert((char_ptr_b != NULL));

	// use the standard library's string comparison function
	return strcmp(a, b);
}