Weird bit-printing behavior—run it and see what happens

gistfile1.m

#import <Foundation/Foundation.h>

static NSString *int32tostr(int value);

int main(int argc, char *argv[]) {
	@autoreleasepool {
		NSLog(@"%@", int32tostr(1));
		NSLog(@"%@", int32tostr(2));
		NSLog(@"%@", int32tostr(3));
	}
}

static NSString *int32tostr(int value) {
	unsigned int uval = (unsigned int)value;
#if BIG_ENDIAN
	unsigned int bigvalue = uval;
#elif LITTLE_ENDIAN
	unsigned int bigvalue = NSSwapHostIntToBig(uval);
#endif
	enum {
		numBits = sizeof(value) * 8,
		numOutputChars = numBits + 1
	};
	char buf[numOutputChars];
	signed int i = numBits;
	while (i > -1) {
		unsigned int j = numBits - i;
		buf[j] = '0' + ((bigvalue >> i) & 1);
		--i;
	}
	buf[numBits] = '\0';
	NSString *str = [NSString stringWithUTF8String:buf];
	return str;
}

gistfile2.m

//Version that works
#import <Foundation/Foundation.h>

static const char *int32tostr(int value);

int main(int argc, char *argv[]) {
	@autoreleasepool {
		for(int i = 0; i < 16; ++i) {
			printf("%s\n", int32tostr(i));
		}
	}
}

static const char *int32tostr(int value) {
	unsigned int uval = (unsigned int)value;
#if BIG_ENDIAN
	unsigned int bigvalue = uval;
#elif LITTLE_ENDIAN
	unsigned int bigvalue = NSSwapHostIntToBig(uval);
#endif
	enum {
		numBits = sizeof(value) * 8,
		numOutputChars = numBits + 1
	};
	static char buf[numOutputChars];
	signed int i = numBits;
	while (i > -1) {
		buf[numBits - (i + 1)] = '0' + ((bigvalue >> i) & 1);
		--i;
	}
	buf[numBits] = '\0';
	return buf;
}