7-2 のプログラムを改良してみました(読みづらくてすいません)

7-2.c

#include <stdio.h>
#define uru_year(a) (!(a % 4)? !(a % 100)? !(a % 400)? 1 : 0 : 1 : 0)

int main(){

	int months[12] = {31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31};
	int from_year, to_year;
	int from_month, to_month;
	int from_day, to_day;
	int from_month_day = 0;
	int year = 0, month = 0, day = 0;

	printf("計算する初めの\n");
	printf("年を入力: ");
	scanf("%d", &from_year);
	printf("月を入力: ");
	scanf("%d", &from_month);
	printf("日にちを入力: ");
	scanf("%d", &from_day);

	printf("\n");

	printf("計算する最後の\n");
	printf("年を入力: ");
	scanf("%d", &to_year);
	printf("月を入力: ");
	scanf("%d", &to_month);
	printf("日にちを入力: ");
	scanf("%d", &to_day);

	/* Fuck point */
	if(to_year - from_year < 0){
		return printf("Fuck you\n");
	} else if(to_year == from_year && to_month - from_month < 0){
		return printf("Fuck you\n");
	} else if (to_year == from_year && to_month == from_month && to_day - from_day < 0){
		return printf("Fuck you\n");
	}

	/* Leap year point */
	int bk_year = from_year;
	if (to_year - from_year > 1){
		while(++bk_year<to_year)
			year += uru_year(bk_year)? 366 : 365;
	}

	/* Month to day point */
	if(from_year != to_year){

		months[1] = uru_year(from_year)? 29 : 28;
		from_month_day = months[(from_month - 1)];

		while(++from_month <= 12)
			month += months[from_month - 1];

		int elements = 0;
		months[1] = uru_year(to_year)? 29 : 28;

		while(elements < (to_month - 1)) 
			month += months[elements++];

	} else {

		while((from_month - 1) < (to_month - 1))
			month += months[from_month++];
	}

	/* Answer */
	day = year + month + (from_month_day - from_day) + to_day;

 	printf("%d日間です。", day);
	
	return 0;

}

7章まだよ。待ってよ笑

閏年判定マクロ最高だな！
けどFuck youはいただけないw